318 research outputs found
Quarkonium above deconfinement as an open quantum system
Quarkonium at temperatures above deconfinement is modeled as an open quantum
system, whose dynamics is determined not just by a potential energy and mass,
but also by a drag coefficient which characterizes its interaction with the
medium. The reduced density matrix for a heavy particle experiencing
dissipative forces is expressed as an integral over paths in imaginary time and
evaluated numerically. We demonstrate that dissipation could affect the
Euclidean heavy-heavy correlators calculated in lattice simulations at
temperatures just above deconfinement.Comment: 13 pages, 1 figur
Effect of spectral modification of on shear viscosity of a pion gas
We evaluate the shear viscosity of a pion gas in the relativistic kinetic
theory approach. The in-medium propagator of the meson at finite
temperature is used to evaluate the scattering amplitude in the
medium. The real and imaginary parts of the self-energy calculated from
one-loop diagrams are seen to have noticeable effects on the scattering
cross-section. The consequences on temperature dependence of the shear
viscosity evaluated in the Chapman-Enskog and relaxation time approximations
are studied
Hard thermal loops with a background plasma velocity
I consider the calculation of the two and three-point functions for QED at
finite temperature in the presence of a background plasma velocity. The final
expressions are consistent with Lorentz invariance, gauge invariance and
current conservation, pointing to a straightforward generalization of the hard
thermal loop formalism to this physical situation. I also give the resulting
expression for the effective action and identify the various terms.Comment: 11 pages, no figure
Quarkonia and Heavy-Quark Relaxation Times in the Quark-Gluon Plasma
A thermodynamic T-matrix approach for elastic 2-body interactions is employed
to calculate spectral functions of open and hidden heavy-quark systems in the
Quark-Gluon Plasma. This enables the evaluation of quarkonium bound-state
properties and heavy-quark diffusion on a common basis and thus to obtain
mutual constraints. The two-body interaction kernel is approximated within a
potential picture for spacelike momentum transfers. An effective
field-theoretical model combining color-Coulomb and confining terms is
implemented with relativistic corrections and for different color channels.
Four pertinent model parameters, characterizing the coupling strengths and
screening, are adjusted to reproduce the color-average heavy-quark free energy
as computed in thermal lattice QCD. The approach is tested against vacuum
spectroscopy in the open (D, B) and hidden (Psi and Upsilon) flavor sectors, as
well as in the high-energy limit of elastic perturbative QCD scattering.
Theoretical uncertainties in the static reduction scheme of the 4-dimensional
Bethe-Salpeter equation are elucidated. The quarkonium spectral functions are
used to calculate Euclidean correlators which are discussed in light of lattice
QCD results, while heavy-quark relaxation rates and diffusion coefficients are
extracted utilizing a Fokker-Planck equation.Comment: 33 pages, 28 figure
Local Approximations for Effective Scalar Field Equations of Motion
Fluctuation and dissipation dynamics is examined at all temperature ranges
for the general case of a background time evolving scalar field coupled to
heavy intermediate quantum fields which in turn are coupled to light quantum
fields. The evolution of the background field induces particle production from
the light fields through the action of the intermediate catalyzing heavy
fields. Such field configurations are generically present in most particle
physics models, including Grand Unified and Supersymmetry theories, with
application of this mechanism possible in inflation, heavy ion collision and
phase transition dynamics. The effective evolution equation for the background
field is obtained and a fluctuation-dissipation theorem is derived for this
system. The effective evolution in general is nonlocal in time. Appropriate
conditions are found for when these time nonlocal effects can be approximated
by local terms. Here careful distinction is made between a local expansion and
the special case of a derivative expansion to all orders, which requires
analytic behavior of the evolution equation in Fourier space.Comment: 14 pages, 2 figures. Replaced with published version. Some extra
typos correcte
Effective potential at finite temperature in a constant magnetic field I: Ring diagrams in a scalar theory
We study symmetry restoration at finite temperature in the theory of a
charged scalar field interacting with a constant, external magnetic field. We
compute the finite temperature effective potential including the contribution
from ring diagrams. We show that in the weak field case, the presence of the
field produces a stronger first order phase transition and that the temperature
for the onset of the transition is lower, as compared to the case without
magnetic field.Comment: Expanded comments, 4 figures added. Conclusions unchanged. Version to
match published pape
Energy and momentum relaxation of heavy fermion in dense and warm plasma
We determine the drag and the momentum diffusion coefficients of heavy
fermion in dense plasma. It is seen that in degenerate matter drag coefficient
at the leading order mediated by transverse photon is proportional to
while for the longitudinal exchange this goes as . We
also calculate the longitudinal diffusion coefficient to obtain the Einstein
relation in a relativistic degenerate plasma. Finally, finite temperature
corrections are included both for the drag and the diffusion coefficients.Comment: 8 pages, 1 eps figure, typos corrected and paragraphs rearranged.
Accepted for publication in Physical Review
Causal amplitudes in the Schwinger model at finite temperature
We show, in the imaginary time formalism, that the temperature dependent
parts of all the retarded (advanced) amplitudes vanish in the Schwinger model.
We trace this behavior to the CPT invariance of the theory and give a physical
interpretation of this result in terms of forward scattering amplitudes of
on-shell thermal particles.Comment: 4 pages with 5 figures, two minor typos corrected, to appear in
Physical Review
Diffusion Enhances Chirality Selection
Diffusion effect on chirality selection in a two-dimensional
reaction-diffusion model is studied by the Monte Carlo simulation. The model
consists of achiral reactants A which turn into either of the chiral products,
R or S, in a solvent of chemically inactive vacancies V. The reaction contains
the nonlinear autocatalysis as well as recycling process, and the chiral
symmetry breaking is monitored by an enantiomeric excess .
Without dilution a strong nonlinear autocatalysis ensures chiral symmetry
breaking. By dilution, the chiral order decreases, and the racemic state
is recovered below the critical concentration . Diffusion effectively
enhances the concentration of chiral species, and decreases as the
diffusion coefficient increases. The relation between and for a
system with a finite fits rather well to an interpolation formula between
the diffusionless(D=0) and homogeneous () limits.Comment: 7 pages, 6 figure
Deterministic constant-temperature dynamics for dissipative quantum systems
A novel method is introduced in order to treat the dissipative dynamics of
quantum systems interacting with a bath of classical degrees of freedom. The
method is based upon an extension of the Nos\`e-Hoover chain (constant
temperature) dynamics to quantum-classical systems. Both adiabatic and
nonadiabatic numerical calculations on the relaxation dynamics of the
spin-boson model show that the quantum-classical Nos\`e-Hoover chain dynamics
represents the thermal noise of the bath in an accurate and simple way.
Numerical comparisons, both with the constant energy calculation and with the
quantum-classical Brownian motion treatment of the bath, show that the
quantum-classical Nos\`e-Hoover Chain dynamics can be used to introduce
dissipation in the evolution of a quantum subsystem even with just one degree
of freedom for the bath. The algorithm can be computationally advantageous in
modeling, within computer simulation, the dynamics of a quantum subsystem
interacting with complex molecular environments.Comment: Revised versio
- …