14533841
New multi-scale supersymmetric models with flavor changing neutral current suppression
Abstract We discuss the phenomenology of a class of supersymmetric models in which some of the quark and lepton superfields are an integral part of a dynamical supersymmetry breaking sector. The corresponding squarks and sleptons are much heavier than any other superpartners, and could naturally have masses as high as ∼ 40 TeV. We discuss a general set of conditions for acceptable flavor-changing neutral currents and natural electroweak symmetry breaking, and identify two particularly interesting new classes of theories. We discuss how phenomenological signatures of such multi-scale models at the CERN LEP II and Fermilab Tevatron colliders could significantly differ from previously considered scenarios. In particular, we give experimental signals which could be present if the left-handed selectron is much lighter than the right-handed one.
13301753
Dynamical supersymmetry breaking at low energies.
Conventional approaches to supersymmetric model building suffer from several naturalness problems: they do not explain the large hierarchy between the weak scale and the Planck mass, and they require fine-tuning to avoid large flavor-changing neutral currents and particle electric dipole moments. The existence of models with dynamical supersymmetry breaking, which can explain the hierarchy, has been known for some time, but efforts to build such models have suffered from unwanted axions and difficulties with asymptotic freedom. In this paper we describe an approach to model building with supersymmetry broken at comparatively low energies which solves these problems, and give a realistic example.
19576396
Short baseline neutrino oscillations and a new light gauge boson
12 pages, 4 figures.-- PACS number: 14.60.Pq.-- Submitted on 8 Nov 2007 (v1), last revised 21 Dec 2007 (this version, v3): References added, minor change to coupling constraints, expanded sections on astrophysical and cosmological constraints.-- Published in: Phys. Rev. D 77, 033001 (2008) (12 pages).-- Final full-text version of the paper available at: http://dx.doi.org/10.1103/PhysRevD.77.033001.
8247001
Fermion mass hierarchy without flavor-changing neutral currents in a technicolor model.
119222841
Apparent CPT violation in neutrino oscillation experiments
We consider searching for light sterile fermions and new forces by using long baseline oscillations of neutrinos and antineutrinos. A new light sterile state and/or a new force can lead to apparent CPT violation in muon neutrino and antineutrino oscillations. As an example, we present an economical model of neutrino masses containing a sterile neutrino. The potential from the standard model weak neutral current gives rise to a difference between the disappearance probabilities of neutrinos and antineutrinos, when mixing with a light sterile neutrino is considered. The addition of a B — L interaction adds coherently to the neutrino current potential and increases the difference between neutrino and antineutrino disappearance. We find that this model can improve the fit to the results of MINOS for both neutrinos and antineutrinos, without any CPT violation, and that the regions of parameter space which improve the fit are within experimental constraints.
34161864
Constraints on neutrino mixing with a 17-keV neutrino.
We examine the constraints on the neutrino mass matrix consistent with the recent rediscovery of a 17-keV neutrino, the absence of neutrinoless double-{beta} decay, and neutrino oscillation experiments. There are two cases consistent with the data, assuming only three Majorana neutrinos. One possibility is that the muon neutrino is heavier than 190 keV, and there is a lower bound on the probability {ital P}{sub {mu}{ital e}} of a muon neutrino oscillating into an electron neutrino, {ital P}{sub {mu}{ital e}}{gt}1.3{times}10{sup {minus}3}. The other possibility is that the muon neutrino is degenerate with the 17-keV neutrino to within an accuracy of 10{sup {minus}11}. In either case, there is a lower limit on the {nu}{sub {ital e}} disappearance probability, {ital P}{sub {ital e}{r arrow}{ital e}}{gt}0.02.
12208225
VINE—A NUMERICAL CODE FOR SIMULATING ASTROPHYSICAL SYSTEMS USING PARTICLES. I. DESCRIPTION OF THE PHYSICS AND THE NUMERICAL METHODS
We present a numerical code for simulating the evolution of astrophysical systems using particles to represent the underlying fluid flow. The code is written in Fortran 95 and is designed to be versatile, flexible and extensible, with modular options that can be selected either at the time the code is compiled or at run time through a text input file. We include a number of general purpose modules describing a variety of physical processes commonly required in the astrophysical community and we expect that the effort required to integrate additional or alternate modules into the code will small. In its simplest form the code can evolve the dynamical trajectories of a set of particles in two or three dimensions using a module which implements either a Leapfrog or Runge-Kutta-Fehlberg integrator, selected by the user at compile time. The user may choose to allow the integrator to evolve the system using individual timesteps for each particle or with a single, global time step for all. Particles may interact gravitationally as N-body particles, and all or any subset may also interact hydrodynamically, using the Smoothed Particle Hydrodynamic (SPH) method by selecting the SPH module. A third particle species can be included with a module to model massive point particles which may accrete nearby SPH or N-body particles. Such particles may be used to model, e.g., stars in a molecular cloud. Free boundary conditions are implemented by default, and a module may be selected to include periodic boundary conditions. We use a binary ‘Press’ tree to organize particles for rapid access in gravity and SPH calculations. Modules implementing an interface with special purpose ‘GRAPE’ hardware may also be selected to accelerate the gravity calculations. If available, forces obtained from the GRAPE coprocessors may be transparently substituted for those obtained from the tree, or both tree and GRAPE may be used as a combination GRAPE/tree code. The code may be run without modification on single processors or in parallel using OpenMP compiler directives on large scale, shared memory parallel machines. We present simulations of several test problems, including a merger simulation of two elliptical galaxies with 800000 particles. In comparison to the Gadget-2 code of Springel (2005), the gravitational force calculation, which is the most costly part of any simulation including self-gravity, is ∼ 4.6 − 4.9 times faster with VINE when tested on different snapshots of the elliptical galaxy merger simulation when run on an Itanium 2 processor in an SGI Altix. A full simulation of the same setup with 8 processors is a factor of 2.91 faster with VINE. The code is available to the public under the terms of the Gnu General Public License. Subject headings: methods: numerical — methods: N-body simulations — galaxies: interactions
5533361
The Range of Masses and Periods Explored by Radial Velocity Searches for Planetary Companions
Radial velocity measurements have proven a powerful tool for finding planets in short-period orbits around other stars. In this paper we develop an analytical expression relating the sensitivity to a periodic signal to the duration and accuracy of a given set of data. The effects of windowing and the sensitivity to periods longer than the total length of observations are explored. We show that current observations are not yet long or accurate enough to make unambiguous detection of planets with the same mass and period as Jupiter. However, if measurements are continued at the current levels of accuracy (5 m s-1) for a decade, then planets of Jovian mass and brown dwarfs will either be detected or ruled out for orbits with periods less than ~15 yr. As specific examples, we outline the performance of our technique on large-amplitude and large-eccentricity radial velocity signals recently discussed in the literature, and we delineate the region explored by the measurements of 14 single stars made over a 12 yr period by Walker et al. Had any of these stars shown motion like that caused by the exoplanets recently detected, it would have been easily detected. The data set interesting limits on the presence of brown dwarfs at orbital radii of 5-10 AU. The most significant features in the Walker et al. data are apparent long-term velocity trends in 36 UMa and β Vir, consistent with super planets of mass of 2 MJ in a 10 yr period, or 20-30 MJ in a 50 yr period. If the data are free of long-term systematic errors, the probability of just one of the 14 stars showing this signal by chance is about 15%. Finally, we suggest an observing strategy for future large radial velocity surveys that, if implemented, will allow coverage of the largest range of parameter space with the smallest amount of observing time per star. We suggest that about 10-15 measurements be made of each star in the first 2 yr of the survey, then 2-3 measurements yr-1 thereafter, provided no (or slow) variation is observed. More frequent observations would of course be indicated if such variations were present.
2655191
A proposed origin for chondrule-forming shocks in the solar nebula
We propose that the nebular shocks currently favored as a model to form chondrules and other annealed silicates in the solar nebula originate in the dynamical activity present in the envelope of forming Jovian planets. In contrast to the classic `core accretion model', our 3D hydrodynamic simulations show that this envelope is not a 1D hydrostatic structure but is instead vigorously active and contains densities and temperatures that appear similar in magnitude and spatial extent to those thought to be responsible for the production of chondrules.
16491613
VINE—A NUMERICAL CODE FOR SIMULATING ASTROPHYSICAL SYSTEMS USING PARTICLES. II. IMPLEMENTATION AND PERFORMANCE CHARACTERISTICS
We continue our presentation of VINE. In this paper, we begin with a description of relevant architectural properties of the serial and shared memory parallel computers on which VINE is intended to run, and describe their influences on the design of the code itself. We continue with a detailed description of a number of optimizations made to the layout of the particle data in memory and to our implementation of a binary tree used to access that data for use in gravitational force calculations and searches for SPH neighbor particles. We describe the modifications to the code necessary to obtain forces efficiently from special purpose ‘GRAPE’ hardware, the interfaces required to allow transparent substitution of those forces in the code instead of those obtained from the tree, and the modifications necessary to use both tree and GRAPE together as a fused GRAPE/tree combination. We conclude with an extensive series of performance tests, which demonstrate that the code can be run efficiently and without modification in serial on small workstations or in parallel using the OpenMP compiler directives on large scale, shared memory parallel machines. We analyze the effects of the code optimizations and estimate that they improve its overall performance by more than an order of magnitude over that obtained by many other tree codes. Scaled parallel performance of the gravity and SPH calculations, together the most costly components of most simulations, is nearly linear up to at least 120 processors on moderate sized test problems using the Origin 3000 architecture, and to the maximum machine sizes available to us on several other architectures. At similar accuracy, performance of VINE, used in GRAPE-tree mode, is approximately a factor two slower than that of VINE, used in host-only mode. Further optimizations of the GRAPE/host communications could improve the speed by as much as a factor of three, but have not yet been implemented in VINE. Finally, we find that although parallel performance on small problems may reach a plateau beyond which more processors bring no additional speedup, performance never decreases, a factor important for running large simulations on many processors with individual time steps, where only a small fraction of the total particles require updates at any given moment. Subject headings: methods: numerical — methods: N-body simulations
117045776
Dynamics and observational appearance of circumstellar disks
In my thesis I present a study of the dynamics and observational characteristics of massive circumstellar disks in two dimensions ($r$, $\phi$) using two complimentary hydrodynamic codes: a `Smoothed Particle Hydrodynamic' (SPH) code and a `Piecewise Parabolic Method' (PPM) code. I also study the detection limits available to radial velocity searches for low mass companions to main sequence stars. The thesis is organized as a series of published or submitted papers, connected by introductory and concluding material and is archived `for posterity'. I recommend that readers of this abstract obtain the published versions of each of these papers. I first outline the progress which has been made in the modeling of the structure and origins of the solar system, then in chapter 2 (ApJ 502,p342) I proceed with numerical simulations of circumstellar disks using both hydrodynamic codes assuming a `locally isothermal' equation of state. In chapter 4 (ApJ submitted) I relax the locally isothermal evolution assumption and instead include simple heating and cooling prescriptions for the system. In chapter 6 (ApJ 500,p940) I examine the limits which may be placed upon the detection of planets, brown dwarfs and low mass stellar companions using radial velocity measurements. In chapter 7, I outline several problems which may be profitably addressed by building on this work.