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0704.0101

Paolo Di Vecchia pdv

Paolo Di Vecchia

The birth of string theory

Latex 60 pages, 2 figures, uses svmult.cls. Contribution to the volume "String theory and fundamental interactions", dedicated to Gabriele Veneziano on his 65th birthday.

Lect.NotesPhys.737:59-118,2008

NORDITA-2007-13

hep-th

In this contribution we go through the developments that in the years 1968 to 1974 led from the Veneziano model to the bosonic string.

0704.0102

Steven Dale Cutkosky

Marc Chardin, Steven Dale Cutkosky, Juergen Herzog and Hema Srinivasan

Duality and Tameness

18 pages

math.AC math.AG

We prove a duality theorem for certain graded algebras and show by various examples different kinds of failure of tameness of local cohomology.

0704.0103

Gianluca Gemelli

Gianluca Gemelli

Generalized regularly discontinuous solutions of the Einstein equations

26 pages.

Int.J.Theor.Phys.46:3312-3330,2007

10.1007/s10773-007-9450-y

gr-qc

The physical consistency of the match of piecewise-$C^0$ metrics is discussed. The mathematical theory of gravitational discontinuity hypersurfaces is generalized to cover the match of regularly discontinuous metrics. The mean-value differential geometry framework on a hypersurface is introduced, and corresponding compatibility conditions are deduced. Examples of generalized boundary layers, gravitational shock waves and thin shells are studied.

0704.0104

Michele Grassi

Giovanni Gaiffi, Michele Grassi

A geometric realization of sl(6,C)

16 pages, no figures

math.DG math.RT

Given an orientable weakly self-dual manifold X of rank two, we build a geometric realization of the Lie algebra sl(6,C) as a naturally defined algebra L of endomorphisms of the space of differential forms of X. We provide an explicit description of Serre generators in terms of natural generators of L. This construction gives a bundle on X which is related to the search for a natural Gauge theory on X. We consider this paper as a first step in the study of a rich and interesting algebraic structure.

0704.0105

Michael Entov

Michael Entov and Leonid Polterovich

Rigid subsets of symplectic manifolds

Significant corrections and changes in the part on monotone Lagrangian submanifolds; a comment on the relation between Futaki invariant and mixed action-Maslov homomorphism added

10.1112/S0010437X0900400X

math.SG

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

We show that there is an hierarchy of intersection rigidity properties of sets in a closed symplectic manifold: some sets cannot be displaced by symplectomorphisms from more sets than the others. We also find new examples of rigidity of intersections involving, in particular, specific fibers of moment maps of Hamiltonian torus actions, monotone Lagrangian submanifolds (following the works of P.Albers and P.Biran-O.Cornea), as well as certain, possibly singular, sets defined in terms of Poisson-commutative subalgebras of smooth functions. In addition, we get some geometric obstructions to semi-simplicity of the quantum homology of symplectic manifolds. The proofs are based on the Floer-theoretical machinery of partial symplectic quasi-states.

0704.0106

Xin-Nian Wang

Andreas Schafer, Xin-Nian Wang and Ben-Wei Zhang

Multiple Parton Scattering in Nuclei: Quark-quark Scattering

49 pages in elsart style and 16 figures. Two sentences added, final version appeared in Nucl. Phys. A

Nucl.Phys.A793:128-170,2007

10.1016/j.nuclphysa.2007.06.009

hep-ph nucl-th

Modifications to quark and antiquark fragmentation functions due to quark-quark (antiquark) double scattering in nuclear medium are studied systematically up to order \cal{O}(\alpha_{s}^2)$ in deeply inelastic scattering (DIS) off nuclear targets. At the order $\cal{O}(\alpha_s^2)$, twist-four contributions from quark-quark (antiquark) rescattering also exhibit the Landau-Pomeranchuck-Midgal (LPM) interference feature similar to gluon bremsstrahlung induced by multiple parton scattering. Compared to quark-gluon scattering, the modification, which is dominated by $t$-channel quark-quark (antiquark) scattering, is only smaller by a factor of $C_F/C_A=4/9$ times the ratio of quark and gluon distributions in the medium. Such a modification is not negligible for realistic kinematics and finite medium size. The modifications to quark (antiquark) fragmentation functions from quark-antiquark annihilation processes are shown to be determined by the antiquark (quark) distribution density in the medium. The asymmetry in quark and antiquark distributions in nuclei will lead to different modifications of quark and antiquark fragmentation functions inside a nucleus, which qualitatively explains the experimentally observed flavor dependence of the leading hadron suppression in semi-inclusive DIS off nuclear targets. The quark-antiquark annihilation processes also mix quark and gluon fragmentation functions in the large fractional momentum region, leading to a flavor dependence of jet quenching in heavy-ion collisions.

0704.0107

Igor Grabec

I. Grabec

Experimental modeling of physical laws

12 pages, 5 eps figures, uses svjour.cls

Eur. Phys. J. - B, 22, 129-135 (2001)

10.1007/PL00011130

physics.data-an

A physical law is represented by the probability distribution of a measured variable. The probability density is described by measured data using an estimator whose kernel is the instrument scattering function. The experimental information and data redundancy are defined in terms of information entropy. The model cost function, comprised of data redundancy and estimation error, is minimized by the creation-annihilation process.

0704.0108

Sergey Gubin

Sergey Gubin

Reducing SAT to 2-SAT

8 pages

cs.CC

Description of a polynomial time reduction of SAT to 2-SAT of polynomial size.

0704.0109

Engin Durgun

Engin Durgun, Deniz Cakir, Nurten Akman, and Salim Ciraci

Half-metallic silicon nanowires

5 pagesm 4 figures

cond-mat.mtrl-sci cond-mat.other

From first-principles calculations, we predict that transition metal (TM) atom doped silicon nanowires have a half-metallic ground state. They are insulators for one spin-direction, but show metallic properties for the opposite spin direction. At high coverage of TM atoms, ferromagnetic silicon nanowires become metallic for both spin-directions with high magnetic moment and may have also significant spin-polarization at the Fermi level. The spin-dependent electronic properties can be engineered by changing the type of dopant TM atoms, as well as the diameter of the nanowire. Present results are not only of scientific interest, but can also initiate new research on spintronic applications of silicon nanowires.

0704.0110

Debashish Goswami

Debashish Goswami

On Equivariant Embedding of Hilbert C^* modules

revised substantially, by correcting a wrong argument, pointed out by an anonymous referee (thanks to him/her for this!)

math.OA

We prove that an arbitrary (not necessarily countably generated) Hilbert $G$-$\cla$ module on a G-C^* algebra $\cla$ admits an equivariant embedding into a trivial $G-\cla$ module, provided G is a compact Lie group and its action on $\cla$ is ergodic.

0704.0111

Debashish Goswami

Debashish Goswami

Invariance and the twisted Chern character : a case study

to appear in the proceedings of the conference `Traces in Geometry, Number Theory and Quantum Fields' held in MPI (Bonn), 2005.

math.QA math.KT

We give details of the proof of the remark made in \cite{G2} that the Chern characters of the canonical generators on the K homology of the quantum group $SU_q(2)$ are not invariant under the natural $SU_q(2)$ coaction. Furthermore, the conjecture made in \cite{G2} about the nontriviality of the twisted Chern character coming from an odd equivariant spectral triple on $SU_q(2)$ is settled in the affirmative.

0704.0112

Robert P. C. de Marrais

Robert P. C. de Marrais

Placeholder Substructures III: A Bit-String-Driven ''Recipe Theory'' for Infinite-Dimensional Zero-Divisor Spaces

32 pp., 1 fig. Third of 3-part "theorem/proof" exposition of 78-slide Powerpoint from NKS 2006, available at http://wolframscience.com/conference/2006/presentations/materials/demarrais.ppt V2: small fixes, 2 new notes. V3: Added small number of corrections (pp. 8, 15-16), one long remark (pp. 21-22), RE: 2nd type of box-kite flow pattern

math.RA

Zero-divisors (ZDs) derived by Cayley-Dickson Process (CDP) from N-dimensional hypercomplex numbers (N a power of 2, at least 4) can represent singularities and, as N approaches infinite, fractals -- and thereby,scale-free networks. Any integer greater than 8 and not a power of 2 generates a meta-fractal or "Sky" when it is interpreted as the "strut constant" (S) of an ensemble of octahedral vertex figures called "Box-Kites" (the fundamental building blocks of ZDs). Remarkably simple bit-manipulation rules or "recipes" provide tools for transforming one fractal genus into others within the context of Wolfram's Class 4 complexity.

0704.0113

Xiaolin Li

Xiaolin Li, Li Zhang, Xinran Wang, Iwao Shimoyama, Xiaoming Sun, Won-Seok Seo and Hongjie Dai (Department of Chemistry, Stanford University.)

Langmuir blodgett assembly of densely aligned single walled carbon nanotubes from bulk materials

3 pages, 3 figures. JACS, 2007, in press

10.1021/ja071114e

cond-mat.mtrl-sci

Single walled carbon nanotubes exhibit advanced electrical and surface properties useful for high performance nanoelectronics. Important to future manufacturing of nanotube circuits is large scale assembly of SWNTs into aligned forms. Despite progress in assembly and oriented synthesis, pristine SWNTs in aligned and close-packed form remain elusive and needed for high current, speed and density devices through collective operations of parallel SWNTs. Here, we develop a Langmuir Blodgett method achieving monolayers of aligned SWNTs with dense packing, central to which is a non covalent polymer functionalization by PmPV imparting high solubility and stability of SWNTs in an organic solvent DCE. Pressure cycling or annealing during LB film compression reduces hysteresis and facilitates high degree alignment and packing of SWNTs characterized by microscopy and polarized Raman spectroscopy. The monolayer SWNTs are readily patterned for device integration by microfabrication, enabling the highest currents 3mA through the narrowest regions packed with aligned SWNTs thus far.

0704.0114

Valeri Kotov

Valeri N. Kotov, Dao-Xin Yao, A. H. Castro Neto, D. K. Campbell

Quantum Phase Transition in the Four-Spin Exchange Antiferromagnet

6 pages, 4 figures; published version

Physical Review B 80, 174403 (2009)

10.1103/PhysRevB.80.174403

cond-mat.str-el

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

We study the S=1/2 Heisenberg antiferromagnet on a square lattice with nearest-neighbor and plaquette four-spin exchanges (introduced by A.W. Sandvik, Phys. Rev. Lett. {\bf 98}, 227202 (2007).) This model undergoes a quantum phase transition from a spontaneously dimerized phase to N\'eel order at a critical coupling. We show that as the critical point is approached from the dimerized side, the system exhibits strong fluctuations in the dimer background, reflected in the presence of a low-energy singlet mode, with a simultaneous rise in the triplet quasiparticle density. We find that both singlet and triplet modes of high density condense at the transition, signaling restoration of lattice symmetry. In our approach, which goes beyond mean-field theory in terms of the triplet excitations, the transition appears sharp; however since our method breaks down near the critical point, we argue that we cannot make a definite conclusion regarding the order of the transition.

0704.0115

Yoshifumi Ando

Yoshifumi Ando

Smooth maps with singularities of bounded K-codimensions

Typographic errors are revised and several expressions are modified to better ones

math.GT

We will prove the relative homotopy principle for smooth maps with singularities of a given {\cal K}-invariant class with a mild condition. We next study a filtration of the group of homotopy self-equivalences of a given manifold P by considering singularities of non-negative {\cal K}-codimensions.

0704.0116

Soon-Tae Hong

Yong Seung Cho, Soon-Tae Hong

Stringy Jacobi fields in Morse theory

4 pages, more references are added

Phys.Rev.D75:127902,2007

10.1103/PhysRevD.75.127902

math-ph hep-th math.MP

We consider the variation of the surface spanned by closed strings in a spacetime manifold. Using the Nambu-Goto string action, we induce the geodesic surface equation, the geodesic surface deviation equation which yields a Jacobi field, and we define the index form of a geodesic surface as in the case of point particles to discuss conjugate strings on the geodesic surface.

0704.0117

Mang Feng

T. Liu, K.L. Wang, and M. Feng

Lower ground state due to counter-rotating wave interaction in trapped ion system

Complete solution of a trapped ion in both strong and weak excitation regimes and beyond Lamb-Dicke limit. Also applicable to JC model relevant problems

10.1088/0953-4075/40/11/002

quant-ph

We consider a single ion confined in a trap under radiation of two traveling waves of lasers. In the strong-excitation regime and without the restriction of Lamb-Dicke limit, the Hamiltonian of the system is similar to a driving Jaynes-Cummings model without rotating wave approximation (RWA). The approach we developed enables us to present a complete eigensolutions, which makes it available to compare with the solutions under the RWA. We find that, the ground state in our non-RWA solution is energically lower than the counterpart under the RWA. If we have the ion in the ground state, it is equivalent to a spin dependent force on the trapped ion. Discussion is made for the difference between the solutions with and without the RWA, and for the relevant experimental test, as well as for the possible application in quantum information processing.

0704.0118

Paul Welander

Paul B. Welander and James N. Eckstein

Strained single-crystal Al2O3 grown layer-by-layer on Nb (110) thin films

4 pages, 4 figures, submitted to Appl. Phys. Lett.

10.1063/1.2747675

cond-mat.supr-con cond-mat.mtrl-sci

We report on the layer-by-layer growth of single-crystal Al2O3 thin-films on Nb (110). Single-crystal Nb films are first prepared on A-plane sapphire, followed by the evaporation of Al in an O2 background. The first stages of Al2O3 growth are layer-by-layer with hexagonal symmetry. Electron and x-ray diffraction measurements indicate the Al2O3 initially grows clamped to the Nb lattice with a tensile strain near 10%. This strain relaxes with further deposition, and beyond about 5 nm we observe the onset of island growth. Despite the asymmetric misfit between the Al2O3 film and the Nb under-layer, the observed strain is surprisingly isotropic.

0704.0119

Arumugam Thamizhavel

A. Thamizhavel, R. Kulkarni and S. K. Dhar

Quasi-quartet crystal electric field ground state in a tetragonal CeAg$_2$Ge$_2$ single crystal

2 pages, 2 figures, Submitted to the proceedings of SCES-07, Houston

10.1016/j.physb.2007.10.244

cond-mat.str-el

We have successfully grown the single crystals of CeAg$_2$Ge$_2$, for the first time, by flux method and studied the anisotropic physical properties by measuring the electrical resistivity, magnetic susceptibility and specific heat. We found that CeAg$_2$Ge$_2$ undergoes an antiferromagnetic transition at $T_{\rm N}$ = 4.6 K. The electrical resistivity and susceptibility data reveal strong anisotropic magnetic properties. The magnetization measured at $T$ = 2 K exhibited two metamagnetic transitions at $H_{\rm m1}$ = 31 kOe and $H_{\rm m2}$ = 44.7 kOe, for $H \parallel$ [100] with a saturation magnetization of 1.6 $\mu_{\rm B}$/Ce. The crystalline electric field (CEF) analysis of the inverse susceptibility data reveals that the ground state and the first excited states of CeAg$_2$Ge$_2$ are closely spaced indicating a quasi-quartet ground state. The specific heat data lend further support to the presence of closely spaced energy levels.

0704.0120

Haibo Li

Xiao-Dong Cheng, Kang-Lin He, Hai-Bo Li, Yi-Fang Wang, Mao-Zhi Yang

Strong Phase and $D^0-D^0bar$ mixing at BES-III

6 pages, 1 figure, a typo fixed, add more reference and a few corrections

Phys.Rev.D75:094019,2007

10.1103/PhysRevD.75.094019

hep-ex hep-ph

Most recently, both BaBar and Belle experiments found evidences of neutral $D$ mixing. In this paper, we discuss the constraints on the strong phase difference in $D^0 \to K\pi$ decay from the measurements of the mixing parameters, $y^\prime$, $y_{CP}$ and $x$ at the $B$ factories. The sensitivity of the measurement of the mixing parameter $y$ is estimated in BES-III experiment at $\psi(3770)$ peak. We also make an estimate on the measurements of the mixing rate $R_M$. Finally, the sensitivity of the strong phase difference at BES-III are obtained by using data near the $D\bar{D}$ threshold with CP tag technique at BES-III experiment.

0704.0121

Changhyun Ahn

Changhyun Ahn

Meta-Stable Brane Configuration of Product Gauge Groups

27 pp; 7 figures; Pages 8, 17 and 18 improved and figure 7 corrected; the abstract and introduction improved and to appear in CQG

Class.Quant.Grav.25:075001,2008

10.1088/0264-9381/25/7/075001

hep-th

Starting from the N=1 SU(N_c) x SU(N_c') gauge theory with fundamental and bifundamental flavors, we apply the Seiberg dual to the first gauge group and obtain the N=1 dual gauge theory with dual matters including the gauge singlets. By analyzing the F-term equations of the superpotential, we describe the intersecting type IIA brane configuration for the meta-stable nonsupersymmetric vacua of this gauge theory. By introducing an orientifold 6-plane, we generalize to the case for N=1 SU(N_c) x SO(N_c') gauge theory with fundamental and bifundamental flavors. Finally, the N=1 SU(N_c) x Sp(N_c') gauge theory with matters is also described very briefly.

0704.0122

Masahiro Takahashi

M. Takahashi, Sankalpa Ghosh, T. Mizushima, K. Machida

Spinor dipolar Bose-Einstein condensates; Classical spin approach

5 pages, 5 figures

Phys. Rev. Lett. 98, 260403 (2007)

10.1103/PhysRevLett.98.260403

cond-mat.other

Magnetic dipole-dipole interaction dominated Bose-Einstein condensates are discussed under spinful situations. We treat the spin degrees of freedom as a classical spin vector, approaching from large spin limit to obtain an effective minimal Hamiltonian; a version extended from a non-linear sigma model. By solving the Gross-Pitaevskii equation we find several novel spin textures where the mass density and spin density are strongly coupled, depending upon trap geometries due to the long-range and anisotropic natures of the dipole-dipole interaction.

0704.0123

D. N. Makovetskii

D. N. Makovetskii

Nonlinear Dynamics of the Phonon Stimulated Emission in Microwave Solid-State Resonator of the Nonautonomous Phaser Generator

15 pages, 5 figures. Translated from Russian. Originally published in: Radiofizika i Elektronika (Kharkov), 2001, vol.6, no.1, pp.124-134

nlin.CD cond-mat.other physics.optics

The microwave phonon stimulated emission (SE) has been experimentally and numerically investigated in a nonautonomous microwave acoustic quantum generator, called also microwave phonon laser or phaser (see previous works arXiv:cond-mat/0303188 ; arXiv:cond-mat/0402640 ; arXiv:nlin.CG/0703050) Phenomena of branching and long-time refractority (absence of the reaction on the external pulses) for deterministic chaotic and regular processes of SE were observed in experiments with various levels of electromagnetic pumping. At the pumping level growth, the clearly depined increasing of the number of coexisting SE states has been observed both in real physical experiments and in computer simulations. This confirms the analytical estimations of the branching density in the phase space. The nature of the refractority of SE pulses is closely connected with the pointed branching and reflects the crises of strange attractors, i.e. their collisions with unstable periodic components of the higher branches of SE states in the nonautonomous microwave phonon laser.

0704.0124

Alexander Tumanov

Bernard Coupet, Alexandre Sukhov, and Alexander Tumanov

Proper J-holomorphic discs in Stein domains of dimension 2

22 pages; corrected typos, updated list of references

math.CV

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

We prove the existence of global Bishop discs in a strictly pseudoconvex Stein domain in an almost complex manifold of complex dimension 2.

0704.0125

Jens Wirth

Michael Reissig and Jens Wirth

Anisotropic thermo-elasticity in 2D -- Part I: A unified approach

22 pages;

Asymptotic Analysis, 57 No. 1-2, 1-27, 2008

10.3233/ASY-2008-0863

math.AP

In this note we develop tools and techniques for the treatment of anisotropic thermo-elasticity in two space dimensions. We use a diagonalisation technique to obtain properties of the characteristic roots of the full symbol of the system in order to prove $L^p$--$L^q$ decay rates for its solutions.

0704.0126

Huan Yang

Huan Yang, Ying Jia, Lei Shan, Yingzi Zhang, Hai-Hu Wen, Chenggang Zhuang, Zikui Liu, Qi Li, Yi Cui, Xiaoxing Xi

I-V characteristics of the vortex state in MgB2 thin films

7 pages, 9 figures

Phys. Rev. B 76, 134513 (2007)

10.1103/PhysRevB.76.134513

cond-mat.supr-con

The current-voltage (I-V) characteristics of various MgB2 films have been studied at different magnetic fields parallel to c-axis. At fields \mu0H between 0 and 5T, vortex liquid-glass transitions were found in the I-V isotherms. Consistently, the I-V curves measured at different temperatures show a scaling behavior in the framework of quasi-two-dimension (quasi-2D) vortex glass theory. However, at \mu0 H >= 5T, a finite dissipation was observed down to the lowest temperature here, T=1.7K, and the I-V isotherms did not scale in terms of any known scaling law, of any dimensionality. We suggest that this may be caused by a mixture of \sigma band vortices and \pi band quasiparticles. Interestingly, the I-V curves at zero magnetic field can still be scaled according to the quasi-2D vortex glass formalism, indicating an equivalent effect of self-field due to persistent current and applied magnetic field.

0704.0127

Kai Liu

Randy K. Dumas, Chang-Peng Li, Igor V. Roshchin, Ivan K. Schuller and Kai Liu

Magnetic Fingerprints of sub-100 nm Fe Nanodots

19 pages, 4 figures, to appear in PRB

Phys. Rev. B 75, 134405 (2007).

10.1103/PhysRevB.75.134405

cond-mat.mtrl-sci

Sub-100 nm nanomagnets not only are technologically important, but also exhibit complex magnetization reversal behaviors as their dimensions are comparable to typical magnetic domain wall widths. Here we capture magnetic "fingerprints" of 1 billion Fe nanodots as they undergo a single domain to vortex state transition, using a first-order reversal curve (FORC) method. As the nanodot size increases from 52 nm to 67 nm, the FORC diagrams reveal striking differences, despite only subtle changes in their major hysteresis loops. The 52 nm nanodots exhibit single domain behavior and the coercivity distribution extracted from the FORC distribution agrees well with a calculation based on the measured nanodot size distribution. The 58 and 67 nm nanodots exhibit vortex states, where the nucleation and annihilation of the vortices are manifested as butterfly-like features in the FORC distribution and confirmed by micromagnetic simulations. Furthermore, the FORC method gives quantitative measures of the magnetic phase fractions, and vortex nucleation and annihilation fields.

0704.0128

Kim Page

P.A. Evans (1), A.P. Beardmore (1), K.L. Page (1), L.G. Tyler (1), J.P. Osborne (1), M.R. Goad (1), P.T. O'Brien (1), L. Vetere (2), J. Racusin (2), D. Morris (2), D.N. Burrows (2), M. Capalbi (3), M. Perri (3), N. Gehrels (4) and P. Romano (5,6) ((1) University of Leicester, (2) Pennsylvania State University, (3) ASI Science Data Center, (4) NASA/Goddard Space Flight Center, (5) INAF-Osservatorio Astronomico di Brera, (6) Universita' degli Studi di Milano)

An online repository of Swift/XRT light curves of GRBs

8 pages, 6 figures, Accepted for publication in A&A

10.1051/0004-6361:20077530

astro-ph

Context. Swift data are revolutionising our understanding of Gamma Ray Bursts. Since bursts fade rapidly, it is desirable to create and disseminate accurate light curves rapidly. Aims. To provide the community with an online repository of X-ray light curves obtained with Swift. The light curves should be of the quality expected of published data, but automatically created and updated so as to be self-consistent and rapidly available. Methods. We have produced a suite of programs which automatically generates Swift/XRT light curves of GRBs. Effects of the damage to the CCD, automatic readout-mode switching and pile-up are appropriately handled, and the data are binned with variable bin durations, as necessary for a fading source. Results. The light curve repository website (http://www.swift.ac.uk/xrt_curves) contains light curves, hardness ratios and deep images for every GRB which Swift's XRT has observed. When new GRBs are detected, light curves are created and updated within minutes of the data arriving at the UK Swift Science Data Centre.

0704.0129

Alfonso Sorrentino

Alfonso Sorrentino

On the total disconnectedness of the quotient Aubry set

21 pages, accepted for publication in Ergodic Theory Dynam. Systems

math.DS math-ph math.AP math.MP

In this paper we show that the quotient Aubry set associated to certain Lagrangians is totally disconnected (i.e., every connected component consists of a single point). Moreover, we discuss the relation between this problem and a Morse-Sard type property for (difference of) critical subsolutions of Hamilton-Jacobi equations.

0704.0130

Sofiane Bouarroudj

Sofiane Bouarroudj, Pavel Grozman, Dimitry Leites

New simple modular Lie superalgebras as generalized prolongs

20 pages, to appear in Funktsional. Anal. i Prilozhen

Funktsional. Anal. i Prilozhen 42, no. 3, (2008), 1-9; English transl.: Funct. Anal. and its Appl., 42, no. 3, (2008), 161-168.

math.RT

Over algebraically closed fields of characteristic p>2, prolongations of the simple finite dimensional Lie algebras and Lie superalgebras with Cartan matrix are studied for certain simplest gradings of these algebras. Several new simple Lie superalgebras are discovered, serial and exceptional, including superBrown and superMelikyan superalgebras. Simple Lie superalgebras with Cartan matrix of rank 2 are classified.

0704.0131

J. Johansson

J.X. Zheng-Johansson

Vacuum Structure and Potential

8 pages, 2 figures.

physics.gen-ph

Based on overall experimental observations, especially the pair processes, I developed a model structure of the vacuum along with a basic-particle formation scheme begun in 2000 (with collaborator P-I Johansson). The model consists in that the vacuum is, briefly, filled of neutral but polarizable vacuuons, consisting each of a p-vaculeon and n- vaculeon of charges $+e$ and $-e$ of zero rest masses but with spin motions, assumed interacting each other with a Coulomb force. The model has been introduced in full in a book (Nova Sci, 2005) and referred to in a number of journal/E-print papers. I outline in this easier accessible paper the detailed derivation of the model and a corresponding quantitative determination of the vacuuon size.

0704.0132

Vadim S. Khrapai

V.S. Khrapai, S. Ludwig, J.P. Kotthaus, H.P. Tranitz, W. Wegscheider

Counterflow of electrons in two isolated quantum point contacts

as published

Phys. Rev. Lett. 99, 096803 (2007)

10.1103/PhysRevLett.99.096803

cond-mat.mes-hall

We study the interaction between two adjacent but electrically isolated quantum point contacts (QPCs). At high enough source-drain bias on one QPC, the drive QPC, we detect a finite electric current in the second, unbiased, detector QPC. The current generated at the detector QPC always flows in the opposite direction than the current of the drive QPC. The generated current is maximal, if the detector QPC is tuned to a transition region between its quantized conductance plateaus and the drive QPC is almost pinched-off. We interpret this counterflow phenomenon in terms of an asymmetric phonon-induced excitation of electrons in the leads of the detector QPC.

0704.0133

Dieter Lutz

D. Lutz, E. Sturm, L.J. Tacconi, E. Valiante, M. Schweitzer, H. Netzer, R. Maiolino, P. Andreani, O. Shemmer, S. Veilleux

PAH emission and star formation in the host of the z~2.56 Cloverleaf QSO

Accepted for publication as an ApJ Letter. 14 pages, 3 figures.

10.1086/518537

astro-ph

We report the first detection of the 6.2micron and 7.7micron infrared `PAH' emission features in the spectrum of a high redshift QSO, from the Spitzer-IRS spectrum of the Cloverleaf lensed QSO (H1413+117, z~2.56). The ratio of PAH features and rest frame far-infrared emission is the same as in lower luminosity star forming ultraluminous infrared galaxies and in local PG QSOs, supporting a predominantly starburst nature of the Cloverleaf's huge far-infrared luminosity (5.4E12 Lsun, corrected for lensing). The Cloverleaf's period of dominant QSO activity (Lbol ~ 7E13 Lsun) is coincident with an intense (star formation rate ~1000 Msun/yr) and short (gas exhaustion time ~3E7yr) star forming event.

0704.0134

A. K. Chaudhuri

A. K. Chaudhuri

Causal dissipative hydrodynamics for QGP fluid in 2+1 dimensions

Extensively revised version. In the revised version, we have discussed the effect of viscosity on (quark) transverse momentum distribution and on elliptic flow. It was shown that elliptic flow saturates due to non-equilirium correction to the equilibrium distribution function and can not be mimicked by ideal dynamics. 15 pages, 16 figures

nucl-th

In 2nd order causal dissipative theory, space-time evolution of QGP fluid is studied in 2+1 dimensions. Relaxation equations for shear stress tensors are solved simultaneously with the energy-momentum conservation equations. Comparison of evolution of ideal and viscous QGP fluid, initialized under the same conditions, e.g. same equilibration time, energy density and velocity profile, indicate that in a viscous dynamics, energy density or temperature of the fluid evolve slowly, than in an ideal fluid. Cooling gets slower as viscosity increases. Transverse expansion also increases in a viscous dynamics. For the first time we have also studied elliptic flow of 'quarks' in causal viscous dynamics. It is shown that elliptic flow of quarks saturates due to non-equilibrium correction to equilibrium distribution function, and can not be mimicked by an ideal hydrodynamics.

0704.0135

Nicolas Menicucci

Nicolas C. Menicucci and G. J. Milburn

A Single Trapped Ion as a Time-Dependent Harmonic Oscillator

5 pages (two-column format), no figures, added introductory material, other minor content revisions

Phys. Rev. A 76, 052105 (2007)

10.1103/PhysRevA.76.052105

quant-ph

We show how a single trapped ion may be used to test a variety of important physical models realized as time-dependent harmonic oscillators. The ion itself functions as its own motional detector through laser-induced electronic transitions. Alsing et al. [Phys. Rev. Lett. 94, 220401 (2005)] proposed that an exponentially decaying trap frequency could be used to simulate (thermal) Gibbons-Hawking radiation in an expanding universe, but the Hamiltonian used was incorrect. We apply our general solution to this experimental proposal, correcting the result for a single ion and showing that while the actual spectrum is different from the Gibbons-Hawking case, it nevertheless shares an important experimental signature with this result.

0704.0136

Zihua Weng

Zihua Weng

Compounding Fields and Their Quantum Equations in the Trigintaduonion Space

17 pages

physics.gen-ph

The 32-dimensional compounding fields and their quantum interplays in the trigintaduonion space can be presented by analogy with octonion and sedenion electromagnetic, gravitational, strong and weak interactions. In the trigintaduonion fields which are associated with the electromagnetic, gravitational, strong and weak interactions, the study deduces some conclusions of field source particles (quarks and leptons) and intermediate particles which are consistent with current some sorts of interaction theories. In the trigintaduonion fields which are associated with the hyper-strong and strong-weak fields, the paper draws some predicts and conclusions of the field source particles (sub-quarks) and intermediate particles. The research results show that there may exist some new particles in the nature.

0704.0137

Suresh Tiwari dr

S C Tiwari

Topological defects, geometric phases, and the angular momentum of light

No figures

Optik-International Journal for Light and Electron Optics, 120, 414-417 (2009)

quant-ph

Recent reports on the intriguing features of vector vortex bearing beams are analyzed using geometric phases in optics. It is argued that the spin redirection phase induced circular birefringence is the origin of topological phase singularities arising in the inhomogeneous polarization patterns. A unified picture of recent results is presented based on this proposition. Angular momentum shift within the light beam (OAM) has exact equivalence with the angular momentum holonomy associated with the geometric phase consistent with our conjecture.

0704.0138

Enrico Barausse

Enrico Barausse, Scott A. Hughes, Luciano Rezzolla

Circular and non-circular nearly horizon-skimming orbits in Kerr spacetimes

15 pages, 4 figures, 5 tables. Small changes following referee's suggestion, typos corrected. Accepted for publication in PRD

Phys.Rev.D76:044007,2007

10.1103/PhysRevD.76.044007

gr-qc astro-ph

We have performed a detailed analysis of orbital motion in the vicinity of a nearly extremal Kerr black hole. For very rapidly rotating black holes (spin a=J/M>0.9524M) we have found a class of very strong field eccentric orbits whose angular momentum L_z increases with the orbit's inclination with respect to the equatorial plane, while keeping latus rectum and eccentricity fixed. This behavior is in contrast with Newtonian intuition, and is in fact opposite to the "normal" behavior of black hole orbits. Such behavior was noted previously for circular orbits; since it only applies to orbits very close to the black hole, they were named "nearly horizon-skimming orbits". Our analysis generalizes this result, mapping out the full generic (inclined and eccentric) family of nearly horizon-skimming orbits. The earlier work on circular orbits reported that, under gravitational radiation emission, nearly horizon-skimming orbits tend to evolve to smaller orbit inclination, toward prograde equatorial configuration. Normal orbits, by contrast, always demonstrate slowly growing orbit inclination (orbits evolve toward the retrograde equatorial configuration). Using up-to-date Teukolsky-fluxes, we have concluded that the earlier result was incorrect: all circular orbits, including nearly horizon-skimming ones, exhibit growing orbit inclination. Using kludge fluxes based on a Post-Newtonian expansion corrected with fits to circular and to equatorial Teukolsky-fluxes, we argue that the inclination grows also for eccentric nearly horizon-skimming orbits. We also find that the inclination change is, in any case, very small. As such, we conclude that these orbits are not likely to have a clear and peculiar imprint on the gravitational waveforms expected to be measured by the space-based detector LISA.

0704.0139

Barbara Lanzoni

B. Lanzoni (1,2), E. Dalessandro (1,2), F.R. Ferraro (1), C. Mancini (3), G. Beccari (2,4,5), R.T. Rood (6), M. Mapelli (7), S. Sigurdsson (8) (1 Dip. Astro., Bologna; 2 INAF--Oss. Astro., Bologna, 3 Dip. Astro. e Scienza dello Spazio, Firenze; 4 Dip. di Scienze della Comunicazione, Teramo; 5 INAF--Oss. Astro. di Collurania, Teramo; 6 Dep. of Astronomy and Astrophysics, The Pennsylvania State University; 7 S.I.S.S.A., Via Beirut 2 - 4, Trieste; 8 Astronomy Department, University of Virginia)

The Blue Straggler Population of the Globular Cluster M5

ApJ accepted

Astrophys.J.663:267-276,2007

10.1086/518592

astro-ph

By combining high-resolution HST and wide-field ground based observations, in ultraviolet and optical bands, we study the Blue Stragglers Star (BSS) population of the galactic globular cluster M5 (NGC 5904) from its very central regions up to its periphery. The BSS distribution is highly peaked in the cluster center, decreases at intermediate radii and rises again outward. Such a bimodal distribution is similar to those previously observed in other globular clusters (M3, 47Tucanae, NGC6752). As for these clusters, dynamical simulations suggest that, while the majority of BSS in M5 could be originated by stellar collisions, a significant fraction (20-40%) of BSS generated by mass transfer processes in primordial binaries is required to reproduce the observed radial distribution. A candidate BSS has been detected beyond the cluster tidal radius. If confirmed, this could represent an interesting case of an "evaporating" BSS.

0704.0140

Mariano Cadoni

Mariano Cadoni

Entanglement entropy of two-dimensional Anti-de Sitter black holes

6 pages, 2 figures, typos corrected

Phys.Lett.B653:434-438,2007

10.1016/j.physletb.2007.08.026

hep-th

Using the AdS/CFT correspondence we derive a formula for the entanglement entropy of the anti-de Sitter black hole in two spacetime dimensions. The leading term in the large black hole mass expansion of our formula reproduces exactly the Bekenstein-Hawking entropy S_{BH}, whereas the subleading term behaves as ln S_{BH}. This subleading term has the universal form typical for the entanglement entropy of physical systems described by effective conformal fields theories (e.g. one-dimensional statistical models at the critical point). The well-known form of the entanglement entropy for a two-dimensional conformal field theory is obtained as analytic continuation of our result and is related with the entanglement entropy of a black hole with negative mass.

0704.0141

Serguei Molodtsov

S.V. Molodtsov, G.M. Zinovjev

Towards self-consistent definition of instanton liquid parameters

11 pages, 4 figures

JHEP 0812:112,2008

10.1088/1126-6708/2008/12/112

hep-ph

The possibility of self-consistent determination of instanton liquid parameters is discussed together with the definition of optimal pseudo-particle configurations and comparing the various pseudo-particle ensembles. The weakening of repulsive interactions between pseudo-particles is argued and estimated.

0704.0142

J. Kaupuzs

J. Kaupuzs

Some aspects of the nonperturbative renormalization of the phi^4 model

11 pages, no figures. This version is consistent with the accepted (now published) paper.

Int.J.Mod.Phys.B23:5935-5947,2009

10.1142/S0217979209054697

cond-mat.stat-mech

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

A nonperturbative renormalization of the phi^4 model is considered. First we integrate out only a single pair of conjugated modes with wave vectors +/- q. Then we are looking for the RG equation which would describe the transformation of the Hamiltonian under the integration over a shell Lambda - d Lambda < k < Lambda, where d Lambda -> 0. We show that the known Wegner--Houghton equation is consistent with the assumption of a simple superposition of the integration results for +/- q. The renormalized action can be expanded in powers of the phi^4 coupling constant u in the high temperature phase at u -> 0. We compare the expansion coefficients with those exactly calculated by the diagrammatic perturbative method, and find some inconsistency. It causes a question in which sense the Wegner-Houghton equation is really exact.

0704.0143

Serguei Molodtsov

S.V. Molodtsov, G.M. Zinovjev

Instanton Liquid at Finite Temperature and Chemical Potential of Quarks

9 pages, 2 figures

Phys.Part.Nucl.Lett.4:11-17,2007; PismaFiz.Elem.Chast.Atom.Yadra2007N1:25-35,2007

10.1134/S1547477107010037

hep-ph

Instanton liquid in heated and strongly interacting matter is studied using the variational principle. The dependence of the instanton liquid density (gluon condensate) on the temperature and the quark chemical potential is determined under the assumption that, at finite temperatures, the dominant contribution is given by an ensemble of calorons. The respective one-loop effective quark Lagrangian is used.

0704.0144

Dmitry I. Podolsky

D. Podolsky, K. Enqvist

Eternal inflation and localization on the landscape

4 pages; more references added; discussion enlarged

JCAP 0902:007,2009

10.1088/1475-7516/2009/02/007

HIP-2007-15/TH

hep-th astro-ph gr-qc

We model the essential features of eternal inflation on the landscape of a dense discretuum of vacua by the potential $V(\phi)=V_{0}+\delta V(\phi)$, where $|\delta V(\phi)|\ll V_{0}$ is random. We find that the diffusion of the distribution function $\rho(\phi,t)$ of the inflaton expectation value in different Hubble patches may be suppressed due to the effect analogous to the Anderson localization in disordered quantum systems. At $t \to \infty$ only the localized part of the distribution function $\rho (\phi, t)$ survives which leads to dynamical selection principle on the landscape. The probability to measure any but a small value of the cosmological constant in a given Hubble patch on the landscape is exponentially suppressed at $t\to \infty$.

0704.0145

Ghanashyam Date

Ghanashyam Date

Singularity Resolution in Isotropic Loop Quantum Cosmology: Recent Developments

24 pages, no figures.

IMSc/2007/03/2

gr-qc

Since the past Iagrg meeting in December 2004, new developments in loop quantum cosmology have taken place, especially with regards to the resolution of the Big Bang singularity in the isotropic models. The singularity resolution issue has been discussed in terms of physical quantities (expectation values of Dirac observables) and there is also an ``improved'' quantization of the Hamiltonian constraint. These developments are briefly discussed. This is an expanded version of the review talk given at the 24$^{\mathrm{th}}$ IAGRG meeting in February 2007.

0704.0146

Brian Jackson

N. G. Parker, B. Jackson, A. M. Martin, and C. S. Adams

Vortices in Bose-Einstein Condensates: Theory

17 pages, 2 figures. Book chapter to appear in "Emergent Nonlinear Phenomena in Bose-Einstein condensates: Theory and Experiment" (Springer-Verlag).

10.1007/978-3-540-73591-5_9

cond-mat.other

Vortices are pervasive in nature, representing the breakdown of laminar fluid flow and hence playing a key role in turbulence. The fluid rotation associated with a vortex can be parameterized by the circulation $\Gamma=\oint {\rm d}{\bf r}\cdot{\bf v}({\bf r})$ about the vortex, where ${\bf v}({\bf r})$ is the fluid velocity field. While classical vortices can take any value of circulation, superfluids are irrotational, and any rotation or angular momentum is constrained to occur through vortices with quantized circulation. Quantized vortices also play a key role in the dissipation of transport in superfluids. In BECs quantized vortices have been observed in several forms, including single vortices, vortex lattices, and vortex pairs and rings. The recent observation of quantized vortices in a fermionic gas was taken as a clear signature of the underlying condensation and superfluidity of fermion pairs. In addition to BECs, quantized vortices also occur in superfluid Helium, nonlinear optics, and type-II superconductors.

0704.0147

Umesh Vijayashanker

Sudha, A. V. Gopala Rao, A. R. Usha Devi and A. K. Rajagopal

A POVM view of the ensemble approach to polarization optics

14 pages, 1 table; RevTeX

physics.optics physics.class-ph quant-ph

Statistical ensemble formalism of Kim, Mandel and Wolf (J. Opt. Soc. Am. A 4, 433 (1987)) offers a realistic model for characterizing the effect of stochastic non-image forming optical media on the state of polarization of transmittedlight. With suitable choice of the Jones ensemble, various Mueller transformations - some of which have been unknown so far - are deduced. It is observed that the ensemble approach is formally identical to the positive operator valued measures (POVM) on the quantum density matrix. This observation, in combination with the recent suggestion by Ahnert and Payne (Phys. Rev. A 71, 012330, (2005)) - in the context of generalized quantum measurement on single photon polarization states - that linear optics elements can be employed in setting up all possible POVMs, enables us to propose a way of realizing different types of Mueller devices.

0704.0148

Prof. Dr. M. W. Wu

J. H. Jiang, Y. Y. Wang, and M. W. Wu

Reexamination of spin decoherence in semiconductor quantum dots from equation-of-motion approach

20 pages, 13 figures, to be published in PRB

Phys. Rev. B 77, 035323 (2008)

10.1103/PhysRevB.77.035323

cond-mat.mtrl-sci

The longitudinal and transversal spin decoherence times, $T_1$ and $T_2$, in semiconductor quantum dots are investigated from equation-of-motion approach for different magnetic fields, quantum dot sizes, and temperatures. Various mechanisms, such as the hyperfine interaction with the surrounding nuclei, the Dresselhaus spin-orbit coupling together with the electron--bulk-phonon interaction, the $g$-factor fluctuations, the direct spin-phonon coupling due to the phonon-induced strain, and the coaction of the electron--bulk/surface-phonon interaction together with the hyperfine interaction are included. The relative contributions from these spin decoherence mechanisms are compared in detail. In our calculation, the spin-orbit coupling is included in each mechanism and is shown to have marked effect in most cases. The equation-of-motion approach is applied in studying both the spin relaxation time $T_1$ and the spin dephasing time $T_2$, either in Markovian or in non-Markovian limit. When many levels are involved at finite temperature, we demonstrate how to obtain the spin relaxation time from the Fermi Golden rule in the limit of weak spin-orbit coupling. However, at high temperature and/or for large spin-orbit coupling, one has to use the equation-of-motion approach when many levels are involved. Moreover, spin dephasing can be much more efficient than spin relaxation at high temperature, though the two only differs by a factor of two at low temperature.

0704.0149

Eric Gourgoulhon

Eric Gourgoulhon (LUTH, CNRS / Observatoire de Paris / Univ. Paris 7)

Construction of initial data for 3+1 numerical relativity

Minor modifications, updated references, 28 pages, 5 figures, contribution to the Proceedings of the VII Mexican School on Gravitation and Mathematical Physics, held in Playa del Carmen, Mexico (Nov. 26 - Dec. 2, 2006), Journal of Physics: Conference Series, in press

J.Phys.Conf.Ser.91:012001,2007

10.1088/1742-6596/91/1/012001

gr-qc

This lecture is devoted to the problem of computing initial data for the Cauchy problem of 3+1 general relativity. The main task is to solve the constraint equations. The conformal technique, introduced by Lichnerowicz and enhanced by York, is presented. Two standard methods, the conformal transverse-traceless one and the conformal thin sandwich, are discussed and illustrated by some simple examples. Finally a short review regarding initial data for binary systems (black holes and neutron stars) is given.

0704.0150

Bo Gu

Bo Gu and Gang Su

Magnetism and Thermodynamics of Spin-1/2 Heisenberg Diamond Chains in a Magnetic Field

18 pages, 20 figures, to be published in Phys. Rev. B

Phys. Rev. B 75, 174437 (2007)

10.1103/PhysRevB.75.174437

cond-mat.str-el

The magnetic and thermodynamic properties of spin-1/2 Heisenberg diamond chains are investigated in three different cases: (a) J1, J2, J3>0 (frustrated); (b) J1, J3<0, J2>0 (frustrated); and (c) J1, J2>0, J3<0 (non-frustrated). The density matrix renormalization group (DMRG) technique is invoked to study the properties of the system in the ground state, while the transfer matrix renormalization group (TMRG) technique is applied to explore the thermodynamic properties. The local magnetic moments, spin correlation functions, and static structure factors are discussed in the ground state for the three cases. It is shown that the static structure factor S(q) shows peaks at wavevectors $q=a\pi /3$ (a=0,1,2,3,4,5) for different couplings in a zero magnetic field, which, however in the magnetic fields where the magnetization plateau with m=1/6 pertains, exhibits the peaks only at q=0, $2\pi /3$ and $4\pi /3$, which are found to be couplings-independent. The DMRG results of the zero-field static structure factor can be nicely fitted by a linear superposition of six modes, where two fitting equations are proposed. It is observed that the six modes are closely related to the low-lying excitations of the system. At finite temperatures, the double-peak structures of the susceptibility and specific heat against temperature are obtained, where the peak positions and heights are found to depend on the competition of the couplings. It is also uncovered that the XXZ anisotropy of F and AF couplings leads the system of case (c) to display quite different behaviors. In addition, the experimental data of the susceptibility, specific heat and magnetization for the compound Cu$_{3}$(CO$_{3}$)$_{2}$(OH)$_{2}$ are fairly compared with our TMRG results.

0704.0151

Igor Grabec

I. Grabec

Extraction of physical laws from joint experimental data

18 pages, 11 eps figures, uses svjour.cls

Eur. Phys. J. - B, 48, 279-289 (2005)

10.1140/epjb/e2005-00391-0

physics.data-an physics.comp-ph

The extraction of a physical law y=yo(x) from joint experimental data about x and y is treated. The joint, the marginal and the conditional probability density functions (PDF) are expressed by given data over an estimator whose kernel is the instrument scattering function. As an optimal estimator of yo(x) the conditional average is proposed. The analysis of its properties is based upon a new definition of prediction quality. The joint experimental information and the redundancy of joint measurements are expressed by the relative entropy. With the number of experiments the redundancy on average increases, while the experimental information converges to a certain limit value. The difference between this limit value and the experimental information at a finite number of data represents the discrepancy between the experimentally determined and the true properties of the phenomenon. The sum of the discrepancy measure and the redundancy is utilized as a cost function. By its minimum a reasonable number of data for the extraction of the law yo(x) is specified. The mutual information is defined by the marginal and the conditional PDFs of the variables. The ratio between mutual information and marginal information is used to indicate which variable is the independent one. The properties of the introduced statistics are demonstrated on deterministically and randomly related variables.

0704.0152

Alberto Dellafiore

V.I. Abrosimov, D.M. Brink, A.Dellafiore, F. Matera

Kinetic equation for finite systems of fermions with pairing

deeply revised, to be published in Nucl. Phys. A

Nucl.Phys.A800:1-20,2008

10.1016/j.nuclphysa.2007.11.009

nucl-th

The solutions of the Wigner-transformed time-dependent Hartree--Fock--Bogoliubov equations are studied in the constant-$\Delta$ approximation. This approximation is known to violate particle-number conservation. As a consequence, the density fluctuation and the longitudinal response function given by this approximation contain spurious contributions. A simple prescription for restoring both local and global particle-number conservation is proposed. Explicit expressions for the eigenfrequencies of the correlated systems and for the density response function are derived and it is shown that the semiclassical analogous of the quantum single--particle spectrum has an excitation gap of $2\Delta$, in agreement with the quantum result. The collective response is studied for a simplified form of the residual interaction.

0704.0153

Mushfiq Ahmad Mr.

Mushfiq Ahmad

Reciprocal Symmetry and Classical Discrete Oscillator Incorporating Half-Integral Energy Levels

4 pages

physics.gen-ph

Classical oscillator differential equation is replaced by the corresponding (finite time) difference equation. The equation is, then, symmetrized so that it remains invariant under the change d going to -d, where d is the smallest span of time. This symmetric equation has solutions, which come in reciprocally related pairs. One member of a pair agrees with the classical solution and the other is an oscillating solution and does not converge to a limit as d goes to 0. This solution contributes to oscillator energy a term which is a multiple of half-integers.

0704.0154

Ulrich Mosel

Fabian Eichstaedt, Stefan Leupold, Ulrich Mosel, Pascal Muehlich

Hadrons in Medium -- Theory confronts experiment

Key Lecture at YKIS2006, Kyoto, Dec. 2006

Prog.Theor.Phys.Suppl.168:495-502,2007

10.1143/PTPS.168.495

nucl-th hep-ph nucl-ex

In this talk we briefly summarize our theoretical understanding of in-medium selfenergies of hadrons. With the special case of the $\omega$ meson we demonstrate that earlier calculations that predicted a significant lowering of the mass in medium are based on an incorrect treatment of the model Lagrangian; more consistent calculations lead to a significant broadening, but hardly any mass shift. We stress that the experimental reconstruction of hadron spectral functions from measured decay products always requires knowledge of the decay branching ratios which may also be strongly mass-dependent. It also requires a quantitatively reliable treatment of final state interactions which has to be part of any reliable theory.

0704.0155

Floris van der Tak

Floris van der Tak (SRON Groningen), John Black (Onsala), Fredrik Schoeier (Stockholm), David Jansen and Ewine van Dishoeck (Leiden)

A computer program for fast non-LTE analysis of interstellar line spectra

Accepted by A&A; 18 A4 pages, 11 figures

10.1051/0004-6361:20066820

astro-ph

The large quantity and high quality of modern radio and infrared line observations require efficient modeling techniques to infer physical and chemical parameters such as temperature, density, and molecular abundances. We present a computer program to calculate the intensities of atomic and molecular lines produced in a uniform medium, based on statistical equilibrium calculations involving collisional and radiative processes and including radiation from background sources. Optical depth effects are treated with an escape probability method. The program is available on the World Wide Web at http://www.sron.rug.nl/~vdtak/radex/index.shtml . The program makes use of molecular data files maintained in the Leiden Atomic and Molecular Database (LAMDA), which will continue to be improved and expanded. The performance of the program is compared with more approximate and with more sophisticated methods. An Appendix provides diagnostic plots to estimate physical parameters from line intensity ratios of commonly observed molecules. This program should form an important tool in analyzing observations from current and future radio and infrared telescopes.

0704.0156

Han He

Han He, Huaning Wang

Nonlinear force-free coronal magnetic field extrapolation scheme based on the direct boundary integral formulation

This paper has been withdrawn by the authors. This paper has been accepted for publication in JGR-Space Physics. The latest and complete version of the papaer can be downloaded from http://rwcc.bao.ac.cn:8001/swap/NLFFF_DBIE_code/HeHan_NLFFF_JGR.pdf (3.76 MB pdf file)

10.1029/2007JA012441

astro-ph

This paper has been withdrawn by the authors.

0704.0157

Andres Santos

M. Lopez de Haro, S. B. Yuste, and A. Santos

Alternative Approaches to the Equilibrium Properties of Hard-Sphere Liquids

64 pages; 13 figures; to appear in "Playing with Marbles: Theory and Simulation of Hard-Sphere Fluids and Related Systems", edited by A. Mulero (Springer, to be published)

Theory and Simulation of Hard-Sphere Fluids and Related Systems, Lectures Notes in Physics, vol. 753, Angel Mulero, ed. (Springer, Berlin, 2008), pp. 183-245

10.1007/978-3-540-78767-9_6

cond-mat.stat-mech cond-mat.soft physics.chem-ph

An overview of some analytical approaches to the computation of the structural and thermodynamic properties of single component and multicomponent hard-sphere fluids is provided. For the structural properties, they yield a thermodynamically consistent formulation, thus improving and extending the known analytical results of the Percus-Yevick theory. Approximate expressions for the contact values of the radial distribution functions and the corresponding analytical equations of state are also discussed. Extensions of this methodology to related systems, such as sticky hard spheres and square-well fluids, as well as its use in connection with the perturbation theory of fluids are briefly addressed.

0704.0158

Huijie Yang

Fangcui Zhao, Huijie Yang, and Binghong Wang

Complexities of Human Promoter Sequences

5 pages, 3 figures, To appear in Journal of Theoretical Biology

Journal of Theoretical Biology 247 (2007) 645?C649

10.1016/j.jtbi.2007.03.035

q-bio.OT

By means of the diffusion entropy approach, we detect the scale-invariance characteristics embedded in the 4737 human promoter sequences. The exponent for the scale-invariance is in a wide range of $[ {0.3,0.9} ]$, which centered at $\delta_c = 0.66$. The distribution of the exponent can be separated into left and right branches with respect to the maximum. The left and right branches are asymmetric and can be fitted exactly with Gaussian form with different widths, respectively.

0704.0159

Herv\'e Cercellier

H. Cercellier, C. Monney, F. Clerc, C. Battaglia, L. Despont, M. G. Garnier, H. Beck, L. Patthey, H. Berger, P. Aebi

Evidence for an excitonic insulator phase in 1T-TiSe$_{2}$

Submitted to PRL

10.1103/PhysRevLett.99.146403

cond-mat.str-el cond-mat.soft

We present a new high-resolution angle-resolved photoemission study of 1\textit{T}-TiSe$_{2}$ in both, its room-temperature, normal phase and its low-temperature, charge-density wave phase. At low temperature the photoemission spectra are strongly modified, with large band renormalisations at high-symmetry points of the Brillouin zone and a very large transfer of spectral weight to backfolded bands. A theoretical calculation of the spectral function for an excitonic insulator phase reproduces the experimental features with very good agreement. This gives strong evidence in favour of the excitonic insulator scenario as a driving force for the charge-density wave transition in 1\textit{T}-TiSe$_{2}$.

0704.0160

Grazyna Stasinska

G. Stasinska, G. Tenorio-Tagle, M. Rodriguez, W. J. Henney

Oxygen-rich droplets and the enrichment of the ISM

4 pages, 5 colour figures, to be published in the proceedings of the conference "The Metal-Rich Universe", Cambridge University Press

astro-ph

We argue that the discrepancies observed in HII regions between abundances derived from optical recombination lines (ORLs) and collisionally excited lines (CELs) might well be the signature of a scenario of the enrichment of the interstellar medium (ISM) proposed by Tenorio-Tagle (1996). In this scenario, the fresh oxygen released during massive supernova explosions is confined within the hot superbubbles as long as supernovae continue to explode. Only after the last massive supernova explosion, the metal-rich gas starts cooling down and falls on the galaxy within metal-rich droplets. Full mixing of these metal-rich droplets and the ISM occurs during photoionization by the next generations of massive stars. During this process, the metal-rich droplets give rise to strong recombination lines of the metals, leading to the observed ORL-CEL discrepancy. (The full version of this work is submitted to Astronomy and Astrophysics.)

0704.0161

Sharat Chandra

T. R. Ravindran, A. K. Arora, Sharat Chandra, M. C. Valsakumar and N. V. Chandra Shekar

Soft modes and NTE in Zn(CN)2 from Raman spectroscopy and first principles calculations

Submitted to Phys. Rev. Letters

10.1103/PhysRevB.76.054302

cond-mat.mtrl-sci

We have studied Zn(CN)2 at high pressure using Raman spectroscopy, and report Gruneisen parameters of the soft phonons. The phonon frequencies and eigen vectors obtained from ab-initio calculations are used for the assignment of the observed phonon spectra. Out of the eleven zone-centre optical modes, six modes exhibit negative Gruneisen parameter. The calculations suggest that the soft phonons correspond to the librational and translational modes of CN rigid unit, with librational modes contributing more to thermal expansion. A rapid disordering of the lattice is found above 1.6 GPa from X-ray diffraction.

0704.0162

Igor Grabec

I. Grabec

Estimation of experimental data redundancy and related statistics

7 pages, 5 eps figures, uses svjour.cls

physics.data-an physics.comp-ph

Redundancy of experimental data is the basic statistic from which the complexity of a natural phenomenon and the proper number of experiments needed for its exploration can be estimated. The redundancy is expressed by the entropy of information pertaining to the probability density function of experimental variables. Since the calculation of entropy is inconvenient due to integration over a range of variables, an approximate expression for redundancy is derived that includes only a sum over the set of experimental data about these variables. The approximation makes feasible an efficient estimation of the redundancy of data along with the related experimental information and information cost function. From the experimental information the complexity of the phenomenon can be simply estimated, while the proper number of experiments needed for its exploration can be determined from the minimum of the cost function. The performance of the approximate estimation of these statistics is demonstrated on two-dimensional normally distributed random data.

0704.0163

Peter Brommer

Peter Brommer and Franz G\"ahler (Institut f\"ur Theoretische und Angewandte Physik, Universit\"at Stuttgart)

Effective potentials for quasicrystals from ab-initio data

7 pages, 1 figure, Proceedings of International Conference on Quasicrystals 9

Philosophical Magazine 86 (2006), 753

10.1080/14786430500333349

cond-mat.mtrl-sci

Classical effective potentials are indispensable for any large-scale atomistic simulations, and the relevance of simulation results crucially depends on the quality of the potentials used. For complex alloys like quasicrystals, however, realistic effective potentials are practically inexistent. We report here on our efforts to develop effective potentials especially for quasicrystalline alloy systems. We use the so-called force matching method, in which the potential parameters are adapted so as to optimally reproduce the forces and energies in a set of suitably chosen reference configurations. These reference data are calculated with ab-initio methods. As a first application, EAM potentials for decagonal Al-Ni-Co, icosahedral Ca-Cd, and both icosahedral and decagonal Mg-Zn quasicrystals have been constructed. The influence of the potential range and degree of specialisation on the accuracy and other properties is discussed and compared.

0704.0164

Lilia Rosati

Lilia Rosati

On smooth foliations with Morse singularities

15 pages, 14 figures

math.GT

Let $M$ be a smooth manifold and let $\F$ be a codimension one, $C^\infty$ foliation on $M$, with isolated singularities of Morse type. The study and classification of pairs $(M,\F)$ is a challenging (and difficult) problem. In this setting, a classical result due to Reeb \cite{Reeb} states that a manifold admitting a foliation with exactly two center-type singularities is a sphere. In particular this is true if the foliation is given by a function. Along these lines a result due to Eells and Kuiper \cite{Ku-Ee} classify manifolds having a real-valued function admitting exactly three non-degenerate singular points. In the present paper, we prove a generalization of the above mentioned results. To do this, we first describe the possible arrangements of pairs of singularities and the corresponding codimension one invariant sets, and then we give an elimination procedure for suitable center-saddle and some saddle-saddle configurations (of consecutive indices). In the second part, we investigate if other classical results, such as Haefliger and Novikov (Compact Leaf) theorems, proved for regular foliations, still hold true in presence of singularities. At this purpose, in the singular set, $Sing(\F)$ of the foliation $\F$, we consider {\em{weakly stable}} components, that we define as those components admitting a neighborhood where all leaves are compact. If $Sing(\F)$ admits only weakly stable components, given by smoothly embedded curves diffeomorphic to $S^1$, we are able to extend Haefliger's theorem. Finally, the existence of a closed curve, transverse to the foliation, leads us to state a Novikov-type result.

0704.0165

Shlomo Gelaki

Mohammad Abu-Hamed and Shlomo Gelaki

Frobenius-Schur indicators for semisimple Lie algebras

12 pages, to appear in Journal of Algebra

math.QA math.RT

Let g be a finite dimensional complex semisimple Lie algebra, and let V be a finite dimensional represenation of g. We give a closed formula for the mth Frobenius-Schur indicator, m>1, of V in representation-theoretic terms. We deduce that the indicators take integer values, and that for a large enough m, the mth indicator of V equals the dimension of the zero weight space of V. For the classical Lie algebras sl(n), so(2n), so(2n+1) and sp(2n), this is the case for m greater or equal to 2n-1, 4n-5, 4n-3 and 2n+1, respectively.

0704.0166

I\~naki Garc\'ia-Etxebarria

Inaki Garcia-Etxebarria, Fouad Saad, Angel M. Uranga

Supersymmetry breaking metastable vacua in runaway quiver gauge theories

26 pages + appendices, 25 figures. v2: Added some acknowledgments

JHEP 0705:047,2007

10.1088/1126-6708/2007/05/047

IFT-UAM/CSIC-07-14, CERN-PH-TH/2007-063

hep-th

In this paper we consider quiver gauge theories with fractional branes whose infrared dynamics removes the classical supersymmetric vacua (DSB branes). We show that addition of flavors to these theories (via additional non-compact branes) leads to local meta-stable supersymmetry breaking minima, closely related to those of SQCD with massive flavors. We simplify the study of the one-loop lifting of the accidental classical flat directions by direct computation of the pseudomoduli masses via Feynman diagrams. This new approach allows to obtain analytic results for all these theories. This work extends the results for the $dP_1$ theory in hep-th/0607218. The new approach allows to generalize the computation to general examples of DSB branes, and for arbitrary values of the superpotential couplings.

0704.0167

Jan O. Eeg

Jan O. Eeg

Low Energy Aspects of Heavy Meson Decays

10 pages, 10 figures. Presented at the final Euridice meeting in Kazimierz, Poland 24-27th of august 2006

ActaPhys.Polon.B38:2869-2878,2007

hep-ph

I discuss low energy aspects of heavy meson decays, where there is at least one heavy meson in the final state. Examples are $B -\bar{B}$ mixing, $B \to D \bar{D}$, $B \to D \eta'$, and $B \to D \gamma$. %and $B \to D W $ (Isgur-Wise function). The analysis is performed in the heavy quark limit within heavy-light chiral perturbation theory. Coefficients of $1/N_c$ suppressed chiral Lagrangian terms (beyond factorization) have been estimated by means of a heavy-light chiral quark model.

0704.0168

Paul Dempsey

Paul Dempsey and Peter Duffy

Radiative losses and cut-offs of energetic particles at relativistic shocks

10 pages, 23 figures and 2 tables. Accepted for publication by MNRAS.

Mon.Not.Roy.Astron.Soc.378:625-634,2007

10.1111/j.1365-2966.2007.11800.x

astro-ph

We investigate the acceleration and simultaneous radiative losses of electrons in the vicinity of relativistic shocks. Particles undergo pitch angle diffusion, gaining energy as they cross the shock by the Fermi mechanism and also emitting synchrotron radiation in the ambient magnetic field. A semi-analytic approach is developed which allows us to consider the behaviour of the shape of the spectral cut-off and the variation of that cut-off with the particle pitch angle. The implications for the synchrotron emission of relativistic jets, such as those in gamma ray burst sources and blazars, are discussed.

0704.0169

Giorgio Calucci

Giorgio Calucci

Very strong and slowly varying magnetic fields as source of axions

8 pages, no figures

Phys.Rev.D75:097303,2007

10.1103/PhysRevD.75.097303

hep-ph

The investigation on the production of particles in slowly varying but extremely intense magnetic field in extended to the case of axions. The motivation is, as for some previously considered cases, the possibility that such kind of magnetic field may exist around very compact astrophysical objects.

0704.0170

Daniele Fausti

Daniele Fausti, Tom T. A. Lummen, Cosmina Angelescu, Roberto Macovez, Javier Luzon, Ria Broer, Petra Rudolf, Paul H.M. van Loosdrecht, Natalia Tristan, Bernd Buchner, Sander van Smaalen, Angela Moller, Gerd Meyer, Timo Taetz

Symmetry disquisition on the TiOX phase diagram

Phys. Rev. B 75, 245114 (2007)

10.1103/PhysRevB.75.245114

cond-mat.str-el cond-mat.mtrl-sci

The sequence of phase transitions and the symmetry of in particular the low temperature incommensurate and spin-Peierls phases of the quasi one-dimensional inorganic spin-Peierls system TiOX (TiOBr and TiOCl) have been studied using inelastic light scattering experiments. The anomalous first-order character of the transition to the spin-Peierls phase is found to be a consequence of the different symmetries of the incommensurate and spin-Peierls (P$2_{1}/m$) phases. The pressure dependence of the lowest transition temperature strongly suggests that magnetic interchain interactions play an important role in the formation of the spin-Peierls and the incommensurate phases. Finally, a comparison of Raman data on VOCl to the TiOX spectra shows that the high energy scattering observed previously has a phononic origin.

0704.0171

Jim Hinton

F. Aharonian, et al

Discovery of a point-like very-high-energy gamma-ray source in Monoceros

5 pages, 4 figures, to appear in A&A

10.1051/0004-6361:20077299

astro-ph

The complex Monoceros Loop SNR/Rosette Nebula region contains several potential sources of very-high-energy (VHE) gamma-ray emission and two as yet unidentified high-energy EGRET sources. Sensitive VHE observations are required to probe acceleration processes in this region. The H.E.S.S. telescope array has been used to search for very high-energy gamma-ray sources in this region. CO data from the NANTEN telescope were used to map the molecular clouds in the region, which could act as target material for gamma-ray production via hadronic interactions. We announce the discovery of a new gamma-ray source, HESS J0632+058, located close to the rim of the Monoceros SNR. This source is unresolved by H.E.S.S. and has no clear counterpart at other wavelengths but is possibly associated with the weak X-ray source 1RXS J063258.3+054857, the Be-star MWC 148 and/or the lower energy gamma-ray source 3EG J0634+0521. No evidence for an associated molecular cloud was found in the CO data.

0704.0172

Anton Ramsak

S. El Shawish, A. Ramsak, and J. Bonca

Thermal entanglement of qubit pairs on the Shastry-Sutherland lattice

10 pages, 9 figures

Phys. Rev. B 75, 205442 (2007)

10.1103/PhysRevB.75.205442

cond-mat.mes-hall cond-mat.str-el

We show that temperature and magnetic field properties of the entanglement between spins on the two-dimensional Shastry-Sutherland lattice can be qualitatively described by analytical results for a qubit tetramer. Exact diagonalization of clusters with up to 20 sites reveals that the regime of fully entangled neighboring pairs coincides with the regime of finite spin gap in the spectrum. Additionally, the results for the regime of vanishing spin gap are discussed and related to the Heisenberg limit of the model.

0704.0173

David Singh

H. Takenaka and D.J. Singh

Bonding of H in O vacancies of ZnO

cond-mat.mtrl-sci

We investigate the bonding of H in O vacancies of ZnO using density functional calculations. We find that H is anionic and does not form multicenter bonds with Zn in this compound.

0704.0174

Miguel Nebot

Francisco J. Botella (Valencia U. & Valencia U., IFIC), Miguel Nebot (Lisbon, IST)

Reparametrization Invariance, the controversial extraction of $\alpha$ from $B\to\pi\pi$ and New Physics

25 pages, 40 figures

IFIC/07-17, FTUV-07-0402

hep-ph hep-ex

The extraction of the weak phase $\alpha$ from $B\to\pi\pi$ decays has been controversial from a statistical point of view, as the frequentist vs. bayesian confrontation shows. We analyse several relevant questions which have not deserved full attention and pervade the extraction of $\alpha$. Reparametrization Invariance proves appropriate to understand those issues. We show that some Standard Model inspired parametrizations can be senseless or inadequate if they go beyond the minimal Gronau and London assumptions: the single weak phase $\alpha$ just in the $\Delta I=3/2$ amplitudes, the isospin relations and experimental data. Beside those analyses, we extract $\alpha$ through the use of several adequate parametrizations, showing that there is no relevant discrepancy between frequentist and bayesian results. The most relevant information, in terms of $\alpha$, is the exclusion of values around $\alpha\sim \pi/4$; this result is valid in the presence of arbitrary New Physics contributions to the $\Delta I=1/2$ piece.

0704.0175

Stephen C. Davis

Luca Amendola, Christos Charmousis and Stephen C. Davis

Solar System Constraints on Gauss-Bonnet Mediated Dark Energy

13 pages

JCAP 0710:004,2007

10.1088/1475-7516/2007/10/004

LPT-ORSAY 07-20

astro-ph gr-qc hep-th

Although the Gauss-Bonnet term is a topological invariant for general relativity, it couples naturally to a quintessence scalar field, modifying gravity at solar system scales. We determine the solar system constraints due to this term by evaluating the post-Newtonian metric for a distributional source. We find a mass dependent, 1/r^7 correction to the Newtonian potential, and also deviations from the Einstein gravity prediction for light-bending. We constrain the parameters of the theory using planetary orbits, the Cassini spacecraft data, and a laboratory test of Newton's law, always finding extremely tight bounds on the energy associated to the Gauss-Bonnet term. We discuss the relevance of these constraints to late-time cosmological acceleration.

0704.0176

Li Qunxiang

Jing Huang, Qunxiang Li, Hao Ren, Haibin Su, Q. W. Shi, and Jinlong Yang

Switching mechanism of photochromic diarylethene derivatives molecular junctions

14 pages and 5 figures

10.1063/1.2770733

cond-mat.other cond-mat.mtrl-sci

The electronic transport properties and switching mechanism of single photochromic diarylethene derivatives sandwiched between two gold surfaces with closed and open configurations are investigated by a fully self-consistent nonequilibrium Green's function method combined with density functional theory. The calculated transmission spectra of two configurations are strikingly distinctive. The open form lacks any significant transmission peak within a wide energy window, while the closed structure has two significant transmission peaks on the both sides of the Fermi level. The electronic transport properties of the molecular junction with closed structure under a small bias voltage are mainly determined by the tail of the transmission peak contributed unusually by the perturbed lowest perturbed unoccupied molecular orbital. The calculated on-off ratio of currents between the closed and open configurations is about two orders of magnitude, which reproduces the essential features of the experimental measured results. Moreover, we find that the switching behavior within a wide bias voltage window is extremely robust to both substituting F or S for H or O and varying end anchoring atoms from S to Se and Te.

0704.0177

Alex Greilich

A. Greilich (1), M. Wiemann (1), F. G. G. Hernandez (1), D. R. Yakovlev (1), I. A. Yugova (1), A. Shabaev (2), Al. L. Efros (2), D. Reuter (3), A. D. Wieck (3), and M. Bayer (1) ((1) Universit\"at Dortmund, Germany, (2) Washington, USA, (3) Ruhr-Universit\"at Bochum, Germany)

Robust manipulation of electron spin coherence in an ensemble of singly charged quantum dots

5 Pages, 3 figures

Phys. Rev. B 75, 233301 (2007)

10.1103/PhysRevB.75.233301

physics.optics

Using the recently reported mode locking effect we demonstrate a highly robust control of electron spin coherence in an ensemble of (In,Ga)As quantum dots during the single spin coherence time. The spin precession in a transverse magnetic field can be fully controlled up to 25 K by the parameters of the exciting pulsed laser protocol such as the pulse train sequence, leading to adjustable quantum beat bursts in Faraday rotation. Flipping of the electron spin precession phase was demonstrated by inverting the polarization within a pulse doublet sequence.

0704.0178

Bastian Holst

Bastian Holst, Nadine Nettelmann, Ronald Redmer

Equation of state for dense hydrogen and plasma phase transition

7 pages, 7 figures, contibution to the 12th International Workshop on the Physics of Non-Ideal Plasmas, Darmstadt, Germany

Contrib. Plasma Phys.Volume 47, 368, 2007

10.1002/ctpp.200710049

physics.plasm-ph

We calculate the equation of state of dense hydrogen within the chemical picture. Fluid variational theory is generalized for a multi-component system of molecules, atoms, electrons, and protons. Chemical equilibrium is supposed for the reactions dissociation and ionization. We identify the region of thermodynamic instability which is related to the plasma phase transition. The reflectivity is calculated along the Hugoniot curve and compared with experimental results. The equation-of-state data is used to calculate the pressure and temperature profiles for the interior of Jupiter.

0704.0179

Marco Bellini

Alessandro Zavatta, Valentina Parigi, and Marco Bellini

Experimental nonclassicality of single-photon-added thermal light states

7 pages, 6 figures, accepted for publication in Phys. Rev. A

PHYSICAL REVIEW A 75, 052106 (2007)

10.1103/PhysRevA.75.052106

quant-ph

We report the experimental realization and tomographic analysis of novel quantum light states obtained by exciting a classical thermal field by a single photon. Such states, although completely incoherent, possess a tunable degree of quantumness which is here exploited to put to a stringent experimental test some of the criteria proposed for the proof and the measurement of state non-classicality. The quantum character of the states is also given in quantum information terms by evaluating the amount of entanglement that they can produce.

0704.0180

Vadim A. Rodin

Vadim Rodin

Neutron Skin and Giant Resonances in Nuclei

8 pages, 5 figure; Proceedings of the 28th Int. School on Nuclear Physics "Radioactive Beams, Nuclear Dynamics and Astrophysics", Erice, Italy, Sept. 16-24, 2006. To appear in Prog.Part.Nucl.Phys

Prog.Part.Nucl.Phys.59:268-276,2007

10.1016/j.ppnp.2007.01.023

nucl-th

Some aspects, both experimental and theoretical, of extracting the neutron skin $\Delta R$ from properties of isovector giant resonances are discussed. Existing proposals are critically reviewed. The method relying on the energy difference between the GTR and IAS is shown to lack sensitivity to $\Delta R$. A simple explanation of the linear relation between the symmetry energy and the neutron skin is also given.

0704.0181

Joel Goh

Joel Goh, Ilya Fushman, Dirk Englund, and Jelena Vuckovic

Genetic Optimization of Photonic Bandgap Structures

9 pages, 20 figures

10.1364/OE.15.008218

physics.optics physics.comp-ph

We investigate the use of a Genetic Algorithm (GA) to design a set of photonic crystals (PCs) in one and two dimensions. Our flexible design methodology allows us to optimize PC structures which are optimized for specific objectives. In this paper, we report the results of several such GA-based PC optimizations. We show that the GA performs well even in very complex design spaces, and therefore has great potential for use as a robust design tool in present and future applications.

0704.0182

Wolfgang Kuch

W. Kuch, F. Offi, L. I. Chelaru, J. Wang, K. Fukumoto, M. Kotsugi, J. Kirschner, J. Kunes

Huge magneto-crystalline anisotropy of x-ray linear dichroism observed on Co/FeMn bilayers

Phys. Rev. B 75, 224406 (2007)

10.1103/PhysRevB.75.224406

cond-mat.mtrl-sci

We present an x-ray spectromicroscopic investigation of single-crystalline magnetic FeMn/Co bilayers on Cu(001), using X-ray magnetic circular (XMCD) and linear (XMLD) dichroism at the Co and Fe L3 absorption edges in combination with photoelectron emission microscopy (PEEM). Using the magnetic coupling between the ferromagnetic Co layer and the antiferromagnetic FeMn layer we are able to produce magnetic domains with two different crystallographic orientations of the magnetic easy axis within the same sample at the same time. We find a huge difference in the XMLD contrast between the two types of magnetic domains, which we discuss in terms of intrinsic magneto-crystalline anisotropy of XMLD of the Co layer. We also demonstrate that due to the high sensitivity of the method, the small number of induced ferromagnetic Fe moments at the FeMn-Co interface is sufficient to obtain magnetic contrast from XMLD in a metallic system.

0704.0183

Tekin Dereli

G. Dereli and B. Sungu (Yildiz Tech. Univ., Istanbul)

Temperature Dependence of the Tensile Properties of Single Walled Carbon Nanotubes: O(N) Tight Binding MD Simulation

10.1103/PhysRevB.75.184104

cond-mat.mtrl-sci

This paper examines the effect of temperature on the structural stability and mechanical properties of 20 layered (10,10) single walled carbon nanotubes (SWCNTs) under tensile loading using an O(N) tight binding molecular dynamics (TBMD) simulation method. We observed that (10,10) tube can sustain its structural stability for the strain values of 0.23 in elongation and 0.06 in compression at 300K. Bond breaking strain value decreases with increasing temperature under streching but not under compression. The elastic limit, Young's modulus, tensile strength and Poisson ratio are calculated as 0.10, 0.395 TPa, 83.23 GPa, 0.285, respectively, at 300K. In the temperature range from 300K to 900K; Young's modulus and the tensile strengths are decreasing with increasing temperature while the Poisson ratio is increasing. At higher temperatures, Young's modulus starts to increase while the Poisson ratio and tensile strength decrease. In the temperature range from 1200K to 1800K, the SWCNT is already deformed and softened. Applying strain on these deformed and softened SWCNTs do not follow the same pattern as in the temperature range of 300K to 900K.

0704.0184

Paolo Padovani

P. Padovani (ESO)

Gamma-ray emitting AGN and GLAST

5 pages, 1 figure, invited talk at the First GLAST Symposium, February 5-8, 2007, Stanford University, USA, to appear in the proceedings

AIP Conf.Proc.921:19-23,2007

10.1063/1.2757258

astro-ph

I describe the different classes of Active Galactic Nuclei (AGN) and the basic tenets of unified schemes. I then review the properties of the extragalactic sources detected in the GeV and TeV bands, showing that the vast majority of them belong to the very rare blazar class. I further discuss the kind of AGN GLAST is likely to detect, making some predictions going from the obvious to the likely, all the way to the less probable.

0704.0185

Peter Brommer

Peter Brommer and Franz G\"ahler (Institut f\"ur Theoretische und Angewandte Physik, Universit\"at Stuttgart)

Potfit: effective potentials from ab-initio data

11 pages

Modelling and Simulation in Materials Science and Engineering 15 (2007), 295

10.1088/0965-0393/15/3/008

cond-mat.mtrl-sci

We present a program called potfit which generates an effective atomic interaction potential by matching it to a set of reference data computed in first-principles calculations. It thus allows to perform large-scale atomistic simulations of materials with physically justified potentials. We describe the fundamental principles behind the program, emphasizing its flexibility in adapting to different systems and potential models, while also discussing its limitations. The program has been used successfully in creating effective potentials for a number of complex intermetallic alloys, notably quasicrystals.

0704.0186

Ryo Takahasi

Ryo Takahashi and Morimitsu Tanimoto

Dark energy and neutrino model in SUSY -- Remarks on active and sterile neutrinos mixing --

12 pages, 7 figures, to appear in the proceedings of International Workshop on Neutrino Masses and Mixings -- Toward Unified Understanding of Quark and Lepton Mass Matrices --, Shizuoka, Japan, 17-19 Dec 2006

Int.J.Mod.Phys.E16:1529-1540,2007

10.1142/S0218301307006861

hep-ph

We consider a Mass Varying Neutrinos (MaVaNs) model in supersymmetric theory. The model includes effects of supersymmetry breaking transmitted by the gravitational interaction from the hidden sector, in which supersymmetry was broken, to the dark energy sector. Then evolutions of the neutrino mass and the equation of state parameter of the dark energy are presented in the model. It is remarked that only the mass of a sterile neutrino is variable in the case of the vanishing mixing between the left-handed and a sterile neutrino on cosmological time scale. The finite mixing makes the mass of the left-handed neutrino variable.

0704.0187

Gabor Worseck

G. Worseck (1), C. Fechner (2,3), L. Wisotzki (1) and A. Dall'Aglio (1) ((1) Astrophysikalisches Institut Potsdam, (2) Hamburger Sternwarte, (3) Universit\"at Potsdam)

The transverse proximity effect in spectral hardness on the line of sight towards HE 2347-4342

15 pages, 11 figures, accepted by A&A, major revision of Section 5 following the referee's comments

Astron.Astrophys. 473 (2007) 805

10.1051/0004-6361:20077585

astro-ph

We report the discovery of 14 quasars in the vicinity of HE2347-4342, one of the two quasars whose intergalactic HeII forest has been resolved with FUSE. By analysing the HI and the HeII opacity variations separately, no transverse proximity effect is detected near three foreground quasars of HE2347-4342: QSOJ23503-4328 (z=2.282, $\vartheta=3.59$ arcmin), QSOJ23500-4319 (z=2.302, $\vartheta=8.77$ arcmin) and QSOJ23495-4338 (z=2.690, $\vartheta=16.28$ arcmin). This is primarily due to line contamination and overdensities probably created by large-scale structure. By comparing the HI absorption and the corresponding HeII absorption, we estimated the fluctuating spectral shape of the extragalactic UV radiation field along this line of sight. We find that the UV spectral shape near HE2347-4342 and in the projected vicinity of the three foreground quasars is statistically harder than expected from UV background models dominated by quasars. In addition, we find three highly ionised metal line systems near the quasars. However, they do not yield further constraints on the shape of the ionising field. We conclude that the foreground quasars show a transverse proximity effect that is detectable as a local hardening of the UV radiation field, although the evidence is strongest for QSOJ23495-4338. Thus, the relative spectral hardness traces the proximity effect also in overdense regions prohibiting the traditional detection in the HI forest. Furthermore, we emphasise that softening of quasar radiation by radiative transfer in the intergalactic medium is important to understand the observed spectral shape variations. From the transverse proximity effect of QSOJ23495-4338 we obtain a lower limit on the quasar lifetime of ~25 Myr.

0704.0188

Tanya Elliott

Tanya M Elliott and John F Wheater

Biased random walks on combs

minor changes in technical definitions

J. Phys. A: Math. Theor. 40 (2007) 8265-8288.

10.1088/1751-8113/40/29/005

Oxford University Preprint OUTP-07-04P

cond-mat.other

We develop rigorous, analytic techniques to study the behaviour of biased random walks on combs. This enables us to calculate exactly the spectral dimension of random comb ensembles for any bias scenario in the teeth or spine. Two specific examples of random comb ensembles are discussed; the random comb with nonzero probability of an infinitely long tooth at each vertex on the spine and the random comb with a power law distribution of tooth lengths. We also analyze transport properties along the spine for these probability measures.

0704.0189

Jean-Camille Birget

J. C. Birget

Monoid generalizations of the Richard Thompson groups

31 pages

J. of Pure and Applied Algebra, 213(2) (Feb. 2009) 264-278

math.GR

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

The groups G_{k,1} of Richard Thompson and Graham Higman can be generalized in a natural way to monoids, that we call M_{k,1}, and to inverse monoids, called Inv_{k,1}; this is done by simply generalizing bijections to partial functions or partial injective functions. The monoids M_{k,1} have connections with circuit complexity (studied in another paper). Here we prove that M_{k,1} and Inv_{k,1} are congruence-simple for all k. Their Green relations J and D are characterized: M_{k,1} and Inv_{k,1} are J-0-simple, and they have k-1 non-zero D-classes. They are submonoids of the multiplicative part of the Cuntz algebra O_k. They are finitely generated, and their word problem over any finite generating set is in P. Their word problem is coNP-complete over certain infinite generating sets. Changes in this version: Section 4 has been thoroughly revised, and errors have been corrected; however, the main results of Section 4 do not change. Sections 1, 2, and 3 are unchanged, except for the proof of Theorem 2.3, which was incomplete; a complete proof was published in the Appendix of reference [6], and is also given here.

0704.0190

Eiichi Konishi

E. Konishi (1), Y. Minorikawa (2), V.I. Galkin (3), M. Ishiwata (4), I. Nakamura (4), N. Takahashit (1), M. Kato (5) and A. Misaki (6) ((1) Graduate School of Science and Technology, Hirosaki University (2) School of Science and Engineering, Kinki University (3) Department of Physics, Moscow State University (4) Department of Physics, Saitama University (5) Kyowa Interface Science Co., Ltd., Saitama (6)Advanced Research Institute for Science and Engineering, Waseda University, Tokyo)

The Reliability on the Direction of the Incident Neutrino for the Fully Contained Events and Partially Contained Events due to QEL in the Super-Kamiokande

12 pages 28 figures with 4appendices 4 figures, latex

hep-ex astro-ph hep-ph

In the SK analysis of the neutrino events for [Fully Contained Events] and [Partially Contained Events] on their zenith angle distribution, it is assumed that the zenith angle of the incident neutrino is the same as that of the detected charged lepton. In the present paper, we examine the validity of [the SK assumption on the direction] of the incident neutrinos. Concretely speaking, we analyze muon-like events due to QEL. For the purpose, we develop [Time Sequential Monte Carlo Simulation] to extract the conclusion on the validity of the SK assumption. In our [Time Sequential Simulation], we simulate every physical process concerned as exactly as possible without any approximation. From the comparison between the zenith angle distributon of the emitted muons under [the SK assumption on the direction] and the corresponding one obtained under our [Time Sequential Simulation], it is concluded that the measurement of the direction of the incident neutrino for the neutrino events occurring inside the detector in the SK analysis turns out to be unreliable, which holds irrespective of the existence and/or non-existence of the neutrino oscillation.

0704.0191

Peter Virnau

Peter Virnau (1), Leonid A. Mirny (1,2), Mehran Kardar (1) ((1) Massachusetts Institute of Technology, Department of Physics, Cambridge, MA, United States of America, (2) Massachusetts Institute of Technology, Harvard-MIT Division of Health Science and Technology, Cambridge, MA, United States of America)

Intricate Knots in Proteins: Function and Evolution

6 pages, 2 figures, 1 table

P. Virnau, L. A. Mirny, M. Kardar, PLoS Comp Biol 2, 1074-1079 (2006)

physics.bio-ph physics.data-an q-bio.BM

A number of recently discovered protein structures incorporate a rather unexpected structural feature: a knot in the polypeptide backbone. These knots are extremely rare, but their occurrence is likely connected to protein function in as yet unexplored fashion. Our analysis of the complete Protein Data Bank reveals several new knots which, along with previously discovered ones, can shed light on such connections. In particular, we identify the most complex knot discovered to date in human ubiquitin hydrolase, and suggest that its entangled topology protects it against unfolding and degradation by the proteasome. Knots in proteins are typically preserved across species and sometimes even across kingdoms. However, we also identify a knot which only appears in some transcarbamylases while being absent in homologous proteins of similar structure. The emergence of the knot is accompanied by a shift in the enzymatic function of the protein. We suggest that the simple insertion of a short DNA fragment into the gene may suffice to turn an unknotted into a knotted structure in this protein.

0704.0192

Karen O'Neil

K. O'Neil, S. Oey, G. Bothun

Star Formation in Galaxies with Large Lower Surface Brightness Disks

50 pages; Full paper with all figures available at http://www.gb.nrao.edu/~koneil; Accepted by AJ

10.1086/518831

astro-ph

We present B, R, and Halpha imaging data of 19 large disk galaxies whose properties are intermediate between classical low surface brightness galaxies and ordinary high surface brightness galaxies. We use data taken from the Lowell 1.8m Perkins telescope to determine the galaxies' overall morphology, color, and star formation properties. Morphologically, the galaxies range from Sb through Irr and include galaxies with and without nuclear bars. The colors of the galaxies vary from B-R = 0.3 - 1.9, and most show at least a slight bluing of the colors with increasing radius. The Halpha images of these galaxies show an average star formation rate lower than is found for similar samples with higher surface brightness disks. Additionally, the galaxies studied have both higher gas mass-to-luminosity and diffuse Halpha emission than is found in higher surface brightness samples.

0704.0193

Shengjun Yuan

Shengjun Yuan, Hans De Raedt, Seiji Miyashita

Domain Wall Dynamics near a Quantum Critical Point

to appear in Phys. Rev. B

Phys. Rev. B 75, 184305 (2007)

10.1103/PhysRevB.75.184305

cond-mat.mtrl-sci cond-mat.stat-mech

We study the real-time domain-wall dynamics near a quantum critical point of the one-dimensional anisotropic ferromagnetic spin 1/2 chain. By numerical simulation, we find the domain wall is dynamically stable in the Heisenberg-Ising model. Near the quantum critical point, the width of the domain wall diverges as $(\Delta -1) ^{-1/2}$.

0704.0194

Shmuel Gurvitz

S.A. Gurvitz and D. Mozyrsky

Quantum mechanical approach to decoherence and relaxation generated by fluctuating environment

15 pages, typo errors corrected, version appeared in PRB

Phys. Rev. B77, 075325 (2008)

10.1103/PhysRevB.77.075325

cond-mat.mes-hall quant-ph

We consider an electrostatic qubit, interacting with a fluctuating charge of single electron transistor (SET) in the framework of exactly solvable model. The SET plays a role of the fluctuating environment affecting the qubit's parameters in a controllable way. We derive the rate equations describing dynamics of the entire system for both weak and strong qubit-SET coupling. Solving these equation we obtain decoherence and relaxation rates of the qubit, as well as the spectral density of the fluctuating qubit's parameters. We found that in the weak coupling regime the decoherence and relaxation rates are directly related to the spectral density taken at Rabi or at zero frequency, depending on what a particular qubit's parameters is fluctuating. This relation holds also in the presence of weak back-action of the qubit on the fluctuating environment. In the case of strong back-action, such simple relationship no longer holds, even if the qubit-SET coupling is small. It does not hold either in the strong-coupling regime, even in the absence of the back-action. In addition, we found that our model predicts localization of the qubit in the strong-coupling regime, resembling that of the spin-boson model.

0704.0195

Dmitri Nikshych

Vladimir Drinfeld, Shlomo Gelaki, Dmitri Nikshych, Victor Ostrik

Group-theoretical properties of nilpotent modular categories

23 pages, LaTeX, typos corrected

math.QA math.RT

We characterize a natural class of modular categories of prime power Frobenius-Perron dimension as representation categories of twisted doubles of finite p-groups. We also show that a nilpotent braided fusion category C admits an analogue of the Sylow decomposition. If the simple objects of C have integral Frobenius-Perron dimensions then C is group-theoretical. As a consequence, we obtain that semisimple quasi-Hopf algebras of prime power dimension are group-theoretical. Our arguments are based on a reconstruction of twisted group doubles from Lagrangian subcategories of modular categories (this is reminiscent to the characterization of doubles of quasi-Lie bialgebras in terms of Manin pairs).

0704.0196

Michal Praszalowicz

Karolina Piesciuk, Michal Praszalowicz

Remarks on N_c dependence of decays of exotic baryons

8 pages, 6 figures to be published in proceedings of YKIS06 in Progress of Theoretical Physics. In v2 minor typos corrected

Prog.Theor.Phys.Suppl.168:70-77,2007

10.1143/PTPS.168.70

TPJU-03/2007

hep-ph

We calculate the N_c dependence of the decay widths of exotic eikosiheptaplet within the framework of Chral Quark Soliton Model. We also discuss generalizations of regular baryon representations for arbitrary N_c.

0704.0197

Steffen Schober

Steffen Schober and Martin Bossert

Analysis of random Boolean networks using the average sensitivity

11 pages, 1 figure

nlin.CG

In this work we consider random Boolean networks that provide a general model for genetic regulatory networks. We extend the analysis of James Lynch who was able to proof Kauffman's conjecture that in the ordered phase of random networks, the number of ineffective and freezing gates is large, where as in the disordered phase their number is small. Lynch proved the conjecture only for networks with connectivity two and non-uniform probabilities for the Boolean functions. We show how to apply the proof to networks with arbitrary connectivity $K$ and to random networks with biased Boolean functions. It turns out that in these cases Lynch's parameter $\lambda$ is equivalent to the expectation of average sensitivity of the Boolean functions used to construct the network. Hence we can apply a known theorem for the expectation of the average sensitivity. In order to prove the results for networks with biased functions, we deduct the expectation of the average sensitivity when only functions with specific connectivity and specific bias are chosen at random.

0704.0198

Misael Leon Hilario

L. M. Leon Hilario, A. Bruchhausen, A. M. Lobos, A. A. Aligia

Theory of polariton mediated Raman scattering in microcavities

11 pages, 2 figures

J. Phys.: Condens. Matter 19 (2007) 176210

10.1088/0953-8984/19/176210

cond-mat.str-el cond-mat.other

We calculate the intensity of the polariton mediated inelastic light scattering in semiconductor microcavities. We treat the exciton-photon coupling nonperturbatively and incorporate lifetime effects in both excitons and photons, and a coupling of the photons to the electron-hole continuum. Taking the matrix elements as fitting parameters, the results are in excellent agreement with measured Raman intensities due to optical phonons resonant with the upper polariton branches in II-VI microcavities with embedded CdTe quantum wells.

0704.0199

Christian Krattenthaler

Christian Krattenthaler (Universit\"at Wien) and Thomas M\"uller (Queen Mary & Westfield College, University of London)

Decomposition numbers for finite Coxeter groups and generalised non-crossing partitions

AmS-LaTeX; 65 pages. Final version to appear in Trans. Amer. Math. Soc

Trans. Amer. Math. Soc. 362 (2010), 2723-2787

math.CO math.GR

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

Given a finite irreducible Coxeter group $W$, a positive integer $d$, and types $T_1,T_2,...,T_d$ (in the sense of the classification of finite Coxeter groups), we compute the number of decompositions $c=\si_1\si_2 cdots\si_d$ of a Coxeter element $c$ of $W$, such that $\si_i$ is a Coxeter element in a subgroup of type $T_i$ in $W$, $i=1,2,...,d$, and such that the factorisation is "minimal" in the sense that the sum of the ranks of the $T_i$'s, $i=1,2,...,d$, equals the rank of $W$. For the exceptional types, these decomposition numbers have been computed by the first author. The type $A_n$ decomposition numbers have been computed by Goulden and Jackson, albeit using a somewhat different language. We explain how to extract the type $B_n$ decomposition numbers from results of B\'ona, Bousquet, Labelle and Leroux on map enumeration. Our formula for the type $D_n$ decomposition numbers is new. These results are then used to determine, for a fixed positive integer $l$ and fixed integers $r_1\le r_2\le ...\le r_l$, the number of multi-chains $\pi_1\le \pi_2\le ...\le \pi_l$ in Armstrong's generalised non-crossing partitions poset, where the poset rank of $\pi_i$ equals $r_i$, and where the "block structure" of $\pi_1$ is prescribed. We demonstrate that this result implies all known enumerative results on ordinary and generalised non-crossing partitions via appropriate summations. Surprisingly, this result on multi-chain enumeration is new even for the original non-crossing partitions of Kreweras. Moreover, the result allows one to solve the problem of rank-selected chain enumeration in the type $D_n$ generalised non-crossing partitions poset, which, in turn, leads to a proof of Armstrong's $F=M$ Conjecture in type $D_n$.

0704.0200

Martin Schumacher

Martin Schumacher

Electromagnetic polarizabilities and the excited states of the nucleon

Eur.Phys.J.A31:327-333,2007

10.1140/epja/i2006-10235-1

hep-ph nucl-ex

The electromagnetic polarizabilities of the nucleon are shown to be essentially composed of the nonresonant $\alpha_p(E_{0+})=+3.2$, $\alpha_n(E_{0+})=+4.1$,the $t$-channel $\alpha^t_{p,n}=-\beta^t_{p,n}=+7.6$ and the resonant $\beta_{p,n}(P_{33}(1232))=+8.3$ contributions (in units of $10^{-4}$fm$^3$. The remaining deviations from the experimental data $\Delta\alpha_p=1.2\pm 0.6$, $\Delta\beta_p=1.2\mp 0.6$, \Delta\alpha_n=0.8\pm 1.7$ and $\Delta\beta_n=2.0\mp 1.8$ are contributed by a larger number of resonant and nonresonant processes with cancellations between the contributions. This result confirms that dominant contributions to the electric and magnetic polarizabilities may be represented in terms of two-photon couplings to the $\sigma$-meson having the predicted mass $m_\sigma=666$ MeV and two-photon width $\Gamma_{\gamma\gamma}=2.6$ keV.