931 research outputs found
Dynamical Hartree-Fock-Bogoliubov Theory of Vortices in Bose-Einstein Condensates at Finite Temperature
We present a method utilizing the continuity equation for the condensate
density to make predictions of the precessional frequency of single off-axis
vortices and of vortex arrays in Bose-Einstein condensates at finite
temperature. We also present an orthogonalized Hartree-Fock-Bogoliubov (HFB)
formalism. We solve the continuity equation for the condensate density
self-consistently with the orthogonalized HFB equations, and find stationary
solutions in the frame rotating at this frequency. As an example of the utility
of this formalism we obtain time-independent solutions for
quasi-two-dimensional rotating systems in the co-rotating frame. We compare
these results with time-dependent predictions where we simulate stirring of the
condensate.Comment: 13 pages, 11 figures, 1 tabl
Momentum Space Regularizations and the Indeterminacy in the Schwinger Model
We revisited the problem of the presence of finite indeterminacies that
appear in the calculations of a Quantum Field Theory. We investigate the
occurrence of undetermined mathematical quantities in the evaluation of the
Schwinger model in several regularization scenarios. We show that the
undetermined character of the divergent part of the vacuum polarization tensor
of the model, introduced as an {\it ansatz} in previous works, can be obtained
mathematically if one introduces a set of two parameters in the evaluation of
these quantities. The formal mathematical properties of this tensor and their
violations are discussed. The analysis is carried out in both analytical and
sharp cutoff regularization procedures. We also show how the Pauli Villars
regularization scheme eliminates the indeterminacy, giving a gauge invariant
result in the vector Schwinger model.Comment: 10 pages, no figure
pMSSM Benchmark Models for Snowmass 2013
We present several benchmark points in the phenomenological Minimal
Supersymmetric Standard Model (pMSSM). We select these models as experimentally
well-motivated examples of the MSSM which predict the observed Higgs mass and
dark matter relic density while evading the current LHC searches. We also use
benchmarks to generate spokes in parameter space by scaling the mass parameters
in a manner which keeps the Higgs mass and relic density approximately
constant.Comment: 10 pages, 6 figure
Entanglement renormalization and gauge symmetry
A lattice gauge theory is described by a redundantly large vector space that
is subject to local constraints, and can be regarded as the low energy limit of
an extended lattice model with a local symmetry. We propose a numerical
coarse-graining scheme to produce low energy, effective descriptions of lattice
models with a local symmetry, such that the local symmetry is exactly preserved
during coarse-graining. Our approach results in a variational ansatz for the
ground state(s) and low energy excitations of such models and, by extension, of
lattice gauge theories. This ansatz incorporates the local symmetry in its
structure, and exploits it to obtain a significant reduction of computational
costs. We test the approach in the context of the toric code with a magnetic
field, equivalent to Z2 lattice gauge theory, for lattices with up to 16 x 16
sites (16^2 x 2 = 512 spins) on a torus. We reproduce the well-known ground
state phase diagram of the model, consisting of a deconfined and spin polarized
phases separated by a continuous quantum phase transition, and obtain accurate
estimates of energy gaps, ground state fidelities, Wilson loops, and several
other quantities.Comment: reviewed version as published in PRB; this version includes a new
section about the accuracy of the results several corrections and added
citation
Three-dimensional topological lattice models with surface anyons
We study a class of three dimensional exactly solvable models of topological
matter first put forward by Walker and Wang [arXiv:1104.2632v2]. While these
are not models of interacting fermions, they may well capture the topological
behavior of some strongly correlated systems. In this work we give a full
pedagogical treatment of a special simple case of these models, which we call
the 3D semion model: We calculate its ground state degeneracies for a variety
of boundary conditions, and classify its low-lying excitations. While point
defects in the bulk are confined in pairs connected by energetic strings, the
surface excitations are more interesting: the model has deconfined point
defects pinned to the boundary of the lattice, and these exhibit semionic
braiding statistics. The surface physics is reminiscent of a bosonic
fractional quantum Hall effect in its topological limit, and these
considerations help motivate an effective field theoretic description for the
lattice models as variants of theories. Our special example of the 3D
semion model captures much of the behavior of more general `confined
Walker-Wang models'. We contrast the 3D semion model with the closely related
3D version of the toric code (a lattice gauge theory) which has deconfined
point excitations in the bulk and we discuss how more general models may have
some confined and some deconfined excitations. Having seen that there exist
lattice models whose surfaces have the same topological order as a bosonic
fractional quantum Hall effect on a confining bulk, we construct a lattice
model whose surface has similar topological order to a fermionic quantum hall
effect. We find that in these models a fermion is always deconfined in the
three dimensional bulk
Making the small oblique parameters large
We compute the oblique parameters, including the three new parameters ,
and introduced recently by the Montreal group, for the case of one
scalar multiplet of arbitrary weak isospin and weak hypercharge . We
show that, when the masses of the heaviest and lightest components of the
multiplet remain constant, but increases, the oblique parameter and
the three new oblique parameters increase like , while only
increases like . For large multiplets with masses not much higher than , the oblique parameters and may become much larger than
and .Comment: 9 pages, standard LATEX, 3 figures available from the authors, report
CMU-HEP93-17 and DOE-ER/40682-4
Electron's anomalous magnetic moment effects on electron-hydrogen elastic collisions in the presence of a circularly polarized laser field
The effect of the electron's anomalous magnetic moment on the relativistic
electronic dressing for the process of electron-hydrogen atom elastic
collisions is investigated. We consider a laser field with circular
polarization and various electric field strengths. The Dirac-Volkov states
taking into account this anomaly are used to describe the process in the first
order of perturbation theory. The correlation between the terms coming from
this anomaly and the electric field strength gives rise to new results, namely
the strong dependence of the spinor part of the differential cross section
(DCS) with respect to these terms. A detailed study has been devoted to the non
relativistic regime as well as the moderate relativistic regime. Some aspects
of this dependence as well as the dynamical behavior of the DCS in the
relativistic regime have been addressed.Comment: 1 File Revtex + 14 figures ep
Renormalization Group Running of Newton's G: The Static Isotropic Case
Corrections are computed to the classical static isotropic solution of
general relativity, arising from non-perturbative quantum gravity effects. A
slow rise of the effective gravitational coupling with distance is shown to
involve a genuinely non-perturbative scale, closely connected with the
gravitational vacuum condensate, and thereby, it is argued, related to the
observed effective cosmological constant. Several analogies between the
proposed vacuum condensate picture of quantum gravitation, and non-perturbative
aspects of vacuum condensation in strongly coupled non-abelian gauge theories
are developed. In contrast to phenomenological approaches, the underlying
functional integral formulation of the theory severely constrains possible
scenarios for the renormalization group evolution of couplings. The expected
running of Newton's constant is compared to known vacuum polarization
induced effects in QED and QCD. The general analysis is then extended to a set
of covariant non-local effective field equations, intended to incorporate the
full scale dependence of , and examined in the case of the static isotropic
metric. The existence of vacuum solutions to the effective field equations in
general severely restricts the possible values of the scaling exponent .Comment: 61 pages, 3 figure
Hadronic production of light color-triplet Higgs bosons: an alternative signature for GUT
The conventional signature for grand unified theories (GUT) is the proton
decay. Recently, some models in extra dimensions or with specific discrete
symmetries, which aim at solving the doublet-triplet problem, allow the
color-triplet in the TeV mass region by suppressing the Yukawa couplings of the
triplets to matter fermions. We study the hadronic production and detection of
these TeV colored Higgs bosons as an alternative signature for GUT, which would
behave like massive stable charged particles in particle detectors producing a
striking signature of a charged track in the central tracking system and being
ionized in the outer muon chamber. We found that the LHC is sensitive to a
colored Higgs boson up to about 1.5 TeV. If the color-triplets are stable in
cosmological time scale, they may constitute an interesting fraction of the
dark matter.Comment: We added the description of a model by Goldberger et al.-- a 5D SU(5)
SUSY model in a slice of AdS space with special boundary conditions to
suppress proton decay. The color-triplet also has a TeV mas
Constraints on R-parity violating couplings from LEP/SLD hadronic observables
We analyze the one loop corrections to hadronic Z decays in an R-parity
violating extension to the Minimal Supersymmetric Standard Model (MSSM).
Performing a global fit to all the hadronic observables at the Z-peak, we
obtain stringent constraints on the R-violating couplings constants lambda' and
lambda''. As a result of the strong constraints from the b asymmetry parameters
A_b and A_FB(b), we find that the couplings lambda'{i31}, lambda'{i32}, and
lambda''{321} are ruled out at the 1 sigma level, and that lambda'{i33} and
lambda''{33i} are ruled out at the 2 sigma level. We also obtain Bayesian
confidence limits for the R-violating couplings.Comment: 30 pages, 19 postscript figures, REVTeX, new section 8 on Bayesian
confidence limits adde
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