521 research outputs found
Visualizing Color Plasma Instabilities
I discuss recent advances in the understanding of non-equilibrium gauge field
dynamics in plasmas which have particle distributions which are locally
anisotropic in momentum space. In contrast to locally isotropic plasmas such
anisotropic plasmas have a spectrum of soft unstable modes which are
characterized by exponential growth of transverse (chromo)-magnetic fields at
short times. The long-time behavior of such instabilities depends on whether or
not the gauge group is abelian or non-abelian. I will report on recent
numerical simulations which attempt to determine the long-time behavior of an
anisotropic non-abelian plasma within hard-loop effective theory. For novelty I
will present an interesting method for visualizing the time-dependence of SU(2)
gauge field configurations produced during our numerical simulations.Comment: 10 pages, 5 figures. Contribution to Proceedings of Workshop on
Quark-Gluon-Plasma Thermalization, Vienna, Austria, Aug 10-12. For full
resolution images see
http://www.fias.uni-frankfurt.de/home/strickland/instability
Fermionic dispersion relations in ultradegenerate relativistic plasmas beyond leading logarithmic order
We determine the dispersion relations of fermionic quasiparticles in
ultradegenerate plasmas by a complete evaluation of the on-shell
hard-dense-loop-resummed one-loop fermion self energy for momenta of the order
of the Fermi momentum and above. In the case of zero temperature, we calculate
the nonanalytic terms in the vicinity of the Fermi surface beyond the known
logarithmic approximation, which turn out to involve fractional higher powers
in the energy variable. For nonzero temperature (but much smaller than the
chemical potential), we obtain the analogous expansion in closed form, which is
then analytic but involves polylogarithms. These expansions are compared with a
full numerical evaluation of the resulting group velocities and damping
coefficients.Comment: 9 pages, 2 figures, REVTeX4, v2: minor improvement
Next-to-leading order static gluon self-energy for anisotropic plasmas
In this paper the structure of the next-to-leading (NLO) static gluon self
energy for an anisotropic plasma is investigated in the limit of a small
momentum space anisotropy. Using the Ward identities for the static hard-loop
(HL) gluon polarization tensor and the (nontrivial) static HL vertices, we
derive a comparatively compact form for the complete NLO correction to the
structure function containing the space-like pole associated with magnetic
instabilities. On the basis of a calculation without HL vertices, it has been
conjectured that the imaginary part of this structure function is nonzero,
rendering the space-like poles integrable. We show that there are both positive
and negative contributions when HL vertices are included, highlighting the
necessity of a complete numerical evaluation, for which the present work
provides the basis.Comment: 9 pages, 2 figure
Thermal imaginary part of a real-time static potential from classical lattice gauge theory simulations
Recently, a finite-temperature real-time static potential has been introduced
via a Schr\"odinger-type equation satisfied by a certain heavy quarkonium
Green's function. Furthermore, it has been pointed out that it possesses an
imaginary part, which induces a finite width for the tip of the quarkonium peak
in the thermal dilepton production rate. The imaginary part originates from
Landau-damping of low-frequency gauge fields, which are essentially classical
due to their high occupation number. Here we show how the imaginary part can be
measured with classical lattice gauge theory simulations, accounting
non-perturbatively for the infrared sector of finite-temperature field theory.
We demonstrate that a non-vanishing imaginary part indeed exists
non-perturbatively; and that its value agrees semi-quantitatively with that
predicted by Hard Loop resummed perturbation theory.Comment: 18 pages. v2: clarifications and a reference added; published versio
Radiative heavy quark energy loss in a dynamical QCD medium
The computation of radiative energy loss in a dynamically screened QCD medium
is a key ingredient for obtaining reliable predictions for jet quenching in
ultra-relativistic heavy ion collisions. We calculate, to first order in the
opacity, the energy loss suffered by a heavy quark traveling through an
infinite and time-independent QCD medium and show that the result for a
dynamical medium is almost twice that obtained previously for a medium
consisting of randomly distributed static scattering centers. A quantitative
description of jet suppression in RHIC and LHC experiments thus must correctly
account for the dynamics of the medium's constituents.Comment: 21 pages, 14 figures, submitted to Physical Review
The dynamics of cosmological perturbations in thermal theory
Using a recent thermal-field-theory approach to cosmological perturbations,
the exact solutions that were found for collisionless ultrarelativistic matter
are generalized to include the effects from weak self-interactions in a
model through order . This includes the effects
of a resummation of thermal masses and associated nonlocal gravitational
vertices, thus going far beyond classical kinetic theory. Explicit solutions
for all the scalar, vector, and tensor modes are obtained for a
radiation-dominated Einstein-de Sitter model containing a weakly interacting
scalar plasma with or without the admixture of an independent component of
perfect radiation fluid.Comment: 32 pages, REVTEX, 13 postscript figures included by epsf.st
On the semiclassical mass of -kinks
One-loop mass shifts to the classical masses of stable kinks arising in a
massive non-linear -sigma model are computed. Ultraviolet
divergences are controlled using the heat kernel/zeta function regularization
method. A comparison between the results achieved from exact and
high-temperature asymptotic heat traces is analyzed in depth.Comment: RevTex file, 15 pages, 2 figures. Version to appear in Journal of
Physics
Effective K\"ahler Potentials
We compute the -loop effective K\"ahler potential in the most general
renormalizable supersymmetric quantum field theory.Comment: 11 pages, Late
Quantum Mass and Central Charge of Supersymmetric Monopoles - Anomalies, current renormalization, and surface terms
We calculate the one-loop quantum corrections to the mass and central charge
of N=2 and N=4 supersymmetric monopoles in 3+1 dimensions. The corrections to
the N=2 central charge are finite and due to an anomaly in the conformal
central charge current, but they cancel for the N=4 monopole. For the quantum
corrections to the mass we start with the integral over the expectation value
of the Hamiltonian density, which we show to consist of a bulk contribution
which is given by the familiar sum over zero-point energies, as well as surface
terms which contribute nontrivially in the monopole sector. The bulk
contribution is evaluated through index theorems and found to be nonvanishing
only in the N=2 case. The contributions from the surface terms in the
Hamiltonian are cancelled by infinite composite operator counterterms in the
N=4 case, forming a multiplet of improvement terms. These counterterms are also
needed for the renormalization of the central charge. However, in the N=2 case
they cancel, and both the improved and the unimproved current multiplet are
finite.Comment: 1+40 pages, JHEP style. v2: small corrections and additions,
references adde
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