15090356
Dark Energy and Emergent Spacetime
A natural geometric framework of noncommutative spacetime is symplectic geometry rather than Riemannian geometry. The Darboux theorem in symplectic geometry then admits a novel form of the equivalence principle such that the electromagnetism in noncommutative spacetime can be regarded as a theory of gravity. Remarkably the emergent gravity reveals a noble picture about the origin of spacetime, dubbed as emergent spacetime, which is radically different from any previous physical theory all of which describe what happens in a given spacetime. In particular, the emergent gravity naturally explains the dynamical origin of flat spacetime, which is absent in Einstein gravity: A flat spacetime is not free gratis but a result of Planck energy condensation in a vacuum. This emergent spacetime picture, if it is correct anyway, turns out to be essential to resolve the cosmological constant problem, to understand the nature of dark energy and to explain why gravity is so weak compared to other forces.
12059305
Superstrings and D-branes in A Plane Wave
We carefully analyze the supersymmetry algebra of closed strings and open strings in a type IIB plane wave background. We use eight component chiral spinors, SO(8) MajoranaWeyl spinors, in light-cone gauge to provide a useful basis of string field theory calculation in the plane wave. We consider the two classes of D-branes, D±-branes, and give a worldsheet derivation of conserved supercurrents for all half BPS D-branes preserving 16 supersymmetries in the type IIB plane wave background. We exhaustively provide the supersymmetry algebra of the half BPS branes as well. We also point out that the supersymmetry algebra distinguishes the two SO(4) directions with relative sign which is consistent with the Z2 symmetry of the string action.
12060341
ALE spaces from noncommutative U(1) instantons via exact Seiberg-Witten map
The exact Seiberg–Witten (SW) map of a noncommutative (NC) gauge theory gives the commutative equivalent as an ordinary gauge theory coupled to a field dependent effective metric. We study instanton solutions of this commutative equivalent whose self-duality equation turns out to be the exact SW map of NC instantons. We derive general differential equations governing U(1) instantons and we explicitly get an exact solution corresponding to the single NC instanton. Remarkably the effective metric induced by the single U(1) instanton is related to the Eguchi–Hanson metric—the simplest gravitational instanton. Surprisingly the instanton number is not quantized but depends on an integration constant. Our result confirms the expected non-perturbative breakdown of the SW map. However, the breakdown of the map arises in a consistent way: the instanton number plays the role of a parameter giving rise to a one-parameter family of Eguchi–Hanson metrics.
15769713
A Complete Classification of D-branes in Type IIB Plane Wave Background
We give a complete classification of D-branes in the type IIB plane wave background using Green-Schwarz superstring theory. We find all possible supersymmetric oblique and curved D-branes and consider their intersections. The supersymmetries preserved by various configurations of these D-branes are also identified. In particular, we show that D+-branes of type (+,−, n, n) for n = 1, 2, 3, 4 preserve 4 dynamical supersymmetries by introducing gauge field excitations and newly discovered oblique D5and D7-branes also preserve four or two dynamical supersymmetries with gauge field condensates. Furthermore we find new curved D-branes preserving four dynamical supersymmetries.
18014891
Twisted bundles on noncommutative T4 and D-brane bound states
We construct twisted quantum bundles and adjoint sections on noncommutative $T^4$, and investigate relevant D-brane bound states with non-Abelian backgrounds. We also show that the noncommutative $T^4$ with non-Abelian backgrounds exhibits SO$(4,4|Z)$ duality and via this duality we get a Morita equivalent $T^4$ on which only D0-branes exist. For a reducible non-Abelian background, the moduli space of D-brane bound states in Type II string theory takes the form $\prod_a (T^4)^{q_a}/S_{q_a}$.
118454134
BRST Cohomology and Its Application to QED
We construct the BRST cohomology under a positive definite inner product and obtain the Hodge decomposition theorem at a non-degenerate state vector space $V$. The harmonic states isomorphic with a BRST cohomology class correspond to the physical Hilbert space with positive norm as long as the completeness of $Q_{BRST}$ is satisfied. We explicitly define ``co-BRST'' operator and analyze the quartet mechanism in QED.
16109424
Frequency scanned interferometry for ILC tracker alignment
In this paper, we report high-precision absolute distance and vibration measurements performed with frequency scanned interferometry using a pair of single-mode optical b ers. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. A high-nesse Fabry-Perot interferometer was used to determine frequency changes during scanning. A dual-laser scanning technique was used to cancel drift errors to improve the absolute distance measurement presicion. Under realistic conditions, a precision of 0.16 microns was achieved for absolute distance of 0.41 meters. Numerical simulation of an optical alignment system for a single silicon ladder, cylinder is also presented. The motivation for this project is to design a novel optical system for quasi-real time alignment of tracker detector elements used in High Energy Physics (HEP) experiments. A.F. Fox-Murphy et.al. from Oxford University reported their design of a frequency scanned interferometer (FSI) for precise alignment of the ATLAS Inner Detector [1, 2]. Given the demonstrated need for improvements in detector performance, we plan to design and prototype an enhanced FSI system to be used for the alignment of tracker elements in the next generation of electron-positron Linear Collider detectors. Current plans for future detectors require a spatial resolution for signals from a tracker detector, such as a silicon microstrip or silicon drift detector, to be approximately 7-10 m [3]. To achieve this required spatial resolution, the measurement precision of absolute distance changes of tracker elements in one dimension should be on the order of 1 m . Simultaneous measurements from hundreds of interferometers will be used to determine the 3-dimensional positions of the tracker elements. The University of Michigan group has constructed several demonstration Frequency Scanned Interferometer (FSI) systems with the laser light transported by air or single-mode optical b er, using single-b er and dual-laser scanning techniques for initial feasibility studies. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. The main goal of the demonstration systems was to determine the potential accuracy of absolute distance measurements that could be achieved under both controlled and realistic conditions. Secondary goals included estimating the eects of vibrations and studying error sources crucial to the absolute distance accuracy. Two multiple-distance-measurement analysis techniques were developed to improve distance precision and to extract the amplitude and frequency of vibrations. Under laboratory conditions, a measurement precision of 50 nm was achieved for absolute distances ranging from 0.1 meters to 0.7 meters by using the rst multipledistance-measurement technique. The second analysis technique has the capability to measure vibration frequencies ranging from 0.1 Hz to 100 Hz with amplitude as small as a few nanometers, without a priori knowledge[4]. The multiple-distance-measurement analysis techniques are well suited for reducing vibration eects and uncertainties from fringe & frequency determination, but do not handle well the drift errors such as from thermal eects. In this paper, we describe a dual-laser system intended to reduce the drift errors and show some results under realistic conditions. Numerical simulation of an optical alignment system for a single silicon ladder and for cylinders is also presented.
15148506
Baryon Spectroscopy at Beijing Electron Positron Collider
Baryons are the basic building blocks of our world. If we cut any piece of object smaller and smaller,we will ﬁnally reach the nucleons, i.e., the lightest baryons, and we cannot cut them smaller anyfurther. So without mention any theory, we know that the study of baryon structure is at theforefront of exploring microscopic structure of matter. From theoretical point of view, since baryonsrepresent the simplest system in which the three colors of QCD neutralize into colorless objectsand the essential non-Abelian character of QCD is manifest, understanding the baryon structure isabsolutely necessary before we claim that we really understand QCD.Spectroscopy has long proved to be a powerful tool for exploring internal structures and basicinteractions of microscopic world. Ninety years ago detailed studies of atomic spectroscopy resultedin the great discovery of Niels Bohr’s atomic quantum theory [1]. Forty to sixty years later, stilldetailed studies of nuclear spectroscopy resulted in Nobel Prize winning discoveries of nuclear shellmodel [2] and collective motion model [3] by Aage Bohr et al. Comparing with the atomic andnuclear spectroscopy at those times, our present baryon spectroscopy is still in its infancy [4].Many fundamental issues in baryon spectroscopy are still not well understood [5]. The possibilityof new, as yet unappreciated, symmetries could be addressed with accumulation of more data.The new symmetries may not have obvious relation with QCD, just like nuclear shell model andcollective motion model.Joining the new eﬀort on studying the excited nucleons, N
55601550
Fermion's Tunnelling with Effects of Quantum Gravity
In this paper, using Hamilton-Jacobi method, we address the tunnelling of fermions in a 4-dimensional Schwarzschild spacetime. Based on the generalized uncertainty principle, we introduce 
the influence of quantum gravity. After solving the equation of motion of the spin-1/2 field, we 
derive the corrected Hawking temperature. It turns out that the correction depends not only on 
the black hole’s mass but also on the mass (energy) of emitted fermions. It is of interest that, in 
our calculation, the quantum gravity correction decelerates the temperature increase during the radiation 
explicitly. This observation then naturally leads to the remnants in black hole evaporation. 
Our calculation shows that the residue mass is , where is the Planck mass and is a dimensionless parameter accounting for quantum gravity effects. The evaporation singularity is 
then avoided.
18270173
Identified particle production in p + p and d +Au collisions at RHIC
The BRAHMS experiment at RHIC has measured the transverse momentum spectra of charged pions, kaons and (anti-)protons over a wide range of rapidity in d+Au and p+p collisions at √SNN = 200 GeV. The nuclear modification factor R dAu at forward rapidity shows a clear suppression for π + . The measured net-proton yields in p+p collisions are compared to PYTHIA and HIJING/B and seem to be better described by the latter.
119200112
Double field theory inspired cosmology
Double field theory proposes a generalized spacetime action possessing manifest T-duality on the level of component fields. We calculate the cosmological solutions of double field theory with vanishing Kalb-Ramond field. It turns out that double field theory provides a more consistent way to construct cosmological solutions than the standard string cosmology. We construct solutions for vanishing and non-vanishing symmetry preserving dilaton potentials. The solutions assemble the pre- and post-big bang evolutions in one single line element. Our results show a smooth evolution from an anisotropic early stage to an isotropic phase without any special initial conditions in contrast to previous models. In addition, we demonstrate that the contraction of the dual space automatically leads to both an inflation phase and a decelerated expansion of the ordinary space during different evolution stages.