353 research outputs found
Effective Kinetic Theory for High Temperature Gauge Theories
Quasiparticle dynamics in relativistic plasmas associated with hot,
weakly-coupled gauge theories (such as QCD at asymptotically high temperature
) can be described by an effective kinetic theory, valid on sufficiently
large time and distance scales. The appropriate Boltzmann equations depend on
effective scattering rates for various types of collisions that can occur in
the plasma. The resulting effective kinetic theory may be used to evaluate
observables which are dominantly sensitive to the dynamics of typical
ultrarelativistic excitations. This includes transport coefficients
(viscosities and diffusion constants) and energy loss rates. We show how to
formulate effective Boltzmann equations which will be adequate to compute such
observables to leading order in the running coupling of high-temperature
gauge theories [and all orders in ]. As previously proposed
in the literature, a leading-order treatment requires including both
particle scattering processes as well as effective ``'' collinear
splitting processes in the Boltzmann equations. The latter account for nearly
collinear bremsstrahlung and pair production/annihilation processes which take
place in the presence of fluctuations in the background gauge field. Our
effective kinetic theory is applicable not only to near-equilibrium systems
(relevant for the calculation of transport coefficients), but also to highly
non-equilibrium situations, provided some simple conditions on distribution
functions are satisfied.Comment: 40 pages, new subsection on soft gauge field instabilities adde
Empirical Emission Functions for LPM Suppression of Photon Emission from Quark-Gluon Plasma
The LPM suppression of photon emission rates from the quark gluon plasma have
been studied at different physical conditions of the plasma given by
temperature and chemical potentials.The integral equation for the transverse
vector function (f(p_t)) consisting of multiple scattering effects is solved
for the parameter set {p,k,kappa,T}, for bremsstrahlung and AWS processes. The
peak positions of these distributions depend only on the dynamical variable
x=(T/kappa)|1/p-1/(p+k)|. Integration over these distributions multiplied by
x^2 factor also depends on this variable x,leading to a unique global emission
function g(x) for all parameters. Empirical fits to this dimensionless emission
function, g(x), are obtained. The photon emission rate calculations with LPM
suppression effects reduce to one dimensional integrals involving folding over
the empirical g(x) function with appropriate distribution functions and the
kinematic factors. Using this approach, the suppression factors for both
bremsstrahlung and AWS have been estimated for various chemical potentials and
compared with the variational method
Universality in Voltage-driven Nonequilibrium Phase Transitions
We consider the non-equilibrium ferromagnetic transition of a mesoscopic
sample of a resistive Stoner ferromagnet coupled to two paramagnetic leads. The
transition is controlled by either the lead temperature T or the transport
voltage V applied between the leads. We calculate the T and V dependence of the
magnetization. For systems with a flat density of states we find within
mean-field theory that even at finite bias the magnetization does not depend on
the position along the sample axis, although the charge density and other
quantities do vary. This may be relevant for possible spintronics applications.
In addition, we establish a generalized control parameter in terms of T and V
which allows for a universal description of the temperature- and voltage-driven
transition.Comment: 12 pages, 4 figures. J. Low Temp. Phys., published version.
Discussion of the relation to quantum phase transitions, cond-mat/0607256,
has been adde
A simple sum rule for the thermal gluon spectral function and applications
In this paper, we derive a simple sum rule satisfied by the gluon spectral
function at finite temperature. This sum rule is useful in order to calculate
exactly some integrals that appear frequently in the photon or dilepton
production rate by a quark gluon plasma. Using this sum rule, we rederive
simply some known results and obtain some new results that would be extremely
difficult to justify otherwise. In particular, we derive an exact expression
for the collision integral that appears in the calculation of the
Landau-Pomeranchuk-Migdal effect.Comment: 24 latex pages, 2 postscript figure
The Hydrodynamics of M-Theory
We consider the low energy limit of a stack of N M-branes at finite
temperature. In this limit, the M-branes are well described, via the AdS/CFT
correspondence, in terms of classical solutions to the eleven dimensional
supergravity equations of motion. We calculate Minkowski space two-point
functions on these M-branes in the long-distance, low-frequency limit, i.e. the
hydrodynamic limit, using the prescription of Son and Starinets
[hep-th/0205051]. From these Green's functions for the R-currents and for
components of the stress-energy tensor, we extract two kinds of diffusion
constant and a viscosity. The N dependence of these physical quantities may
help lead to a better understanding of M-branes.Comment: 1+19 pages, references added, section 5 clarified, eq. (72) correcte
Enhanced thermal production of hard dileptons by processes
In the framework of the Hard Thermal Loop effective theory, we calculate the
two-loop contributions to hard lepton pair production in a quark-gluon plasma.
We show that the result is free of any infrared and collinear singularity. We
also recover the known fact that perturbation theory leads to integrable
singularities at the location of the threshold for . It
appears that the process calculated here significantly enhances the rate of low
mass hard dileptons.Comment: 32 latex pages, 14 postscript figure
Symplectic structures associated to Lie-Poisson groups
The Lie-Poisson analogues of the cotangent bundle and coadjoint orbits of a
Lie group are considered. For the natural Poisson brackets the symplectic
leaves in these manifolds are classified and the corresponding symplectic forms
are described. Thus the construction of the Kirillov symplectic form is
generalized for Lie-Poisson groups.Comment: 30 page
Relativistic ponderomotive force, uphill acceleration, and transition to chaos
Starting from a covariant cycle-averaged Lagrangian the relativistic
oscillation center equation of motion of a point charge is deduced and
analytical formulae for the ponderomotive force in a travelling wave of
arbitrary strength are presented. It is further shown that the ponderomotive
forces for transverse and longitudinal waves are different; in the latter,
uphill acceleration can occur. In a standing wave there exists a threshold
intensity above which, owing to transition to chaos, the secular motion can no
longer be described by a regular ponderomotive force.
PACS number(s): 52.20.Dq,05.45.+b,52.35.Mw,52.60.+hComment: 8 pages, RevTeX, 3 figures in PostScript, see also
http://www.physik.th-darmstadt.de/tqe
On Two Complementary Types of Total Time Derivative in Classical Field Theories and Maxwell's Equations
Close insight into mathematical and conceptual structure of classical field
theories shows serious inconsistencies in their common basis. In other words,
we claim in this work to have come across two severe mathematical blunders in
the very foundations of theoretical hydrodynamics. One of the defects concerns
the traditional treatment of time derivatives in Eulerian hydrodynamic
description. The other one resides in the conventional demonstration of the
so-called Convection Theorem. Both approaches are thought to be necessary for
cross-verification of the standard differential form of continuity equation.
Any revision of these fundamental results might have important implications for
all classical field theories. Rigorous reconsideration of time derivatives in
Eulerian description shows that it evokes Minkowski metric for any flow field
domain without any previous postulation. Mathematical approach is developed
within the framework of congruences for general 4-dimensional differentiable
manifold and the final result is formulated in form of a theorem. A modified
version of the Convection Theorem provides a necessary cross-verification for a
reconsidered differential form of continuity equation. Although the approach is
developed for one-component (scalar) flow field, it can be easily generalized
to any tensor field. Some possible implications for classical electrodynamics
are also explored.Comment: no figure
Evolution of Parton Fragmentation Functions at Finite Temperature
The first order correction to the parton fragmentation functions in a thermal
medium is derived in the leading logarithmic approximation in the framework of
thermal field theory. The medium-modified evolution equations of the parton
fragmentation functions are also derived. It is shown that all infrared
divergences, both linear and logarithmic, in the real processes are canceled
among themselves and by corresponding virtual corrections. The evolution of the
quark number and the energy loss (or gain) induced by the thermal medium are
investigated.Comment: 21 pages in RevTex, 10 figure
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