2,486 research outputs found
Non-perturbative determination of anisotropy coefficients in lattice gauge theories
We propose a new non-perturbative method to compute derivatives of gauge
coupling constants with respect to anisotropic lattice spacings (anisotropy
coefficients), which are required in an evaluation of thermodynamic quantities
from numerical simulations on the lattice. Our method is based on a precise
measurement of the finite temperature deconfining transition curve in the
lattice coupling parameter space extended to anisotropic lattices by applying
the spectral density method. We test the method for the cases of SU(2) and
SU(3) gauge theories at the deconfining transition point on lattices with the
lattice size in the time direction -- 6. In both cases, there is a
clear discrepancy between our results and perturbative values. A longstanding
problem, when one uses the perturbative anisotropy coefficients, is a
non-vanishing pressure gap at the deconfining transition point in the SU(3)
gauge theory. Using our non-perturbative anisotropy coefficients, we find that
this problem is completely resolved: we obtain and
on and 6 lattices, respectively.Comment: 24pages,7figures,5table
Spin-orbit lateral superlattices: energy bands and spin polarization in 2DEG
The Bloch spinors, energy spectrum and spin density in energy bands are
studied for the two-dimensional electron gas (2DEG) with Rashba spin-orbit (SO)
interaction subject to one-dimensional (1D) periodic electrostatic potential of
a lateral superlattice. The space symmetry of the Bloch spinors with spin
parity is studied. It is shown that the Bloch spinors at fixed quasimomentum
describe the standing spin waves with the wavelength equal to the superlattice
period. The spin projections in these states have the components both parallel
and transverse to the 2DEG plane. The anticrossing of the energy dispersion
curves due to the interplay between the SO and periodic terms is observed,
leading to the spin flip. The relation between the spin parity and the
interband optical selection rules is discussed, and the effect of magnetization
of the SO superlattice in the presence of external electric field is predicted.Comment: 6 pages, 5 figures, reported at the International Conferences
"Nanophysics and Nanoelectronics" (Nizhny Novgorod, Russia, March 2006) and
"Nanostructures: Physics and Technology" (St Petersburg, Russia, June 2006
Lattice sum rules for the colour fields
We analyse the sum rules describing the action and energy in the colour
fields around glueballs, torelons and static potentials.Comment: 9 pages LATEX, (typos corrected, to appear in Phys Rev D
Screening properties of the two-dimensional electron gas with spin-orbit coupling
We study screening properties of the two-dimensional electron gas with Rashba
spin-orbit coupling. Calculating the dielectric function within the random
phase approximation, we describe the new features of screening induced by
spin-orbit coupling, which are the extension of the region of particle-hole
excitations and the spin-orbit-induced suppression of collective modes. The
required polarization operator is calculated in an analytic form without any
approximations. Carefully deriving its static limit, we prove the absence of a
small- anomaly at zero frequency. On the basis of our results at finite
frequencies we establish the new boundaries of the particle-hole continuum and
calculate the SO-induced lifetime of collective modes such as plasmons and
longitudinal optical phonons. According to our estimates, these effects can be
resolved in inelastic Raman scattering. We evaluate the experimentally
measurable dynamic structure factor and establish the range of parameters where
the described phenomena are mostly pronounced.Comment: 15 pages, 10 figures, extended version of cond-mat/050622
Z2 Monopoles, Vortices, and the Deconfinement Transition in Mixed Action SU(2) Gauge Theory
Adding separate chemical potentials lambda and gamma for Z2 monopoles and
vortices respectively in the Villain form of the mixed fundamental-adjoint
action for the SU(2) lattice gauge theory, we investigate their role in the
interplay between the deconfinement and bulk phase transitions using Monte
Carlo techniques. Setting lambda to be nonzero, we find that the line of
deconfinement transitions is shifted in the coupling plane but it behaves
curiously also like the bulk transition line for large enough adjoint coupling,
as for lambda=0. In a narrow range of couplings, however, we find separate
deconfinement and bulk phase transitions on the same lattice for nonzero and
large lambda, suggesting the two to be indeed coincident in the region where a
first order deconfinement phase transition is seen. In the limit of large
lambda and gamma, we obtain only lines of second order deconfinement phase
transitions, as expected from universality.Comment: 18 pages, 10 figures include
Transverse QCD Dynamics Near the Light Cone
Starting from the QCD Hamiltonian in near-light cone coordinates, we study
the dynamics of the gluonic zero modes. Euclidean 2+1 dimensional lattice
simulations show that the gap at strong coupling vanishes at intermediate
coupling. This result opens the possibility to synchronize the continuum limit
with the approach to the light cone.Comment: 15 pages, LaTeX, 3 figures (7 PS files
Lattice QCD equation of state : improving the differential method
We propose an improvement of the differential method for the computation of
the equation of state of QCD from lattice simulations. In contrast to the
earlier differential method our technique yields positive pressure for all
temperatures including in the transition region. Employing it on temporal
lattices of 8, 10 and 12 sites and by extrapolating to zero lattice spacing we
obtained the pressure, energy density, entropy density, specific heat and speed
of sound in quenched QCD for 0.9 < T/Tc < 3. A comparison of our results is
made with those from the dimensional reduction approach and a conformal
symmetric theory at high-temperature.Comment: Version to be published in Pramana. Title modified. Explanatory
material added. Figure 6b redrawn with corrected normalization for the
AdS/CFT lin
Phase Transitions in SO(3) Lattice Gauge Theory
The phase diagram of SO(3) lattice gauge theory is investigated by Monte
Carlo techniques on both symmetric and asymmetric lattices with a view (i) to
understanding the relationship between the bulk transition and the
deconfinement transition, and (ii) to resolving the current ambiguity about the
nature of the high temperature phase. A number of tests, including an
introduction of a magnetic field and measurement of different correlation
functions in the phases with positive and negative values for the adjoint
Polyakov line, lead to the conclusion that the two phases correspond to the
same physical state. Studies on lattices of different sizes reveal only one
phase transition for this theory on all of them and it appears to have a
deconfining nature.Comment: Latex 19 pages, 9 figures. Minor changes in introduction and summary
sections. The version that appeared in journa
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Dense dark-bright soliton arrays in a two-component Bose-Einstein condensate
We present a combined experimental and theoretical study of regular dark-bright soliton arrays in a two-component atomic Bose-Einstein condensate. We demonstrate a microwave pulse-based winding technique which allows for a tunable number of solitary waves en route to observing their dynamics, quantified through Fourier analysis of the density. We characterize different winding density regimes by the observed dynamics including the decay and revival of the Fourier peaks, the emergence of dark-antidark solitons, and disordering of the soliton array. The experimental results are in good agreement with three-dimensional numerical computations of the underlying mean-field theory. These observations open a window into the study of soliton crystals and the dynamics, excitations, and lifetimes of such patterns
Dual variables for the SU(2) lattice gauge theory at finite temperature
We study the three-dimensional SU(2) lattice gauge theory at finite
temperature using an observable which is dual to the Wilson line. This
observable displays a behaviour which is the reverse of that seen for the
Wilson line. It is non-zero in the confined phase and becomes zero in the
deconfined phase. At large distances, it's correlation function falls off
exponentially in the deconfined phase and remains non-zero in the confined
phase. The dual variable is non-local and has a string attached to it which
creates a Z(2) interface in the system. It's correlation function measures the
string tension between oppositely oriented Z(2) domains. The construction of
this variable can also be made in the four-dimensional theory where it measures
the surface tension between oppositely oriented Z(2) domains.Comment: 13 pages, LaTeX, 4 figures are included in the latex fil
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