252 research outputs found
Photon and electron spectra in hot and dense QED
Photon and electron spectra in hot and dense QED are found in the high
temperature limit for all |\q| using the Feynman gauge and the one-loop
self-energy. All spectra are split by the medium and their branches develop the
gap (the dynamical mass) at zero momentum. The photon spectrum has two branches
(longitudinal and transverse) with the common mass; but electron spectrum is
split on four branches which are well-separated for any |\q| including their
|\q|=0 limits (their effective masses). These masses and the photon thermal
mass are calculated explicitly and the different limits of spectrum branches
are established in detail. The gauge invariance of the high-temperature spectra
is briefly discussed.Comment: 9 pages, latex, no figure
Soliton absorption spectroscopy
We analyze optical soliton propagation in the presence of weak absorption
lines with much narrower linewidths as compared to the soliton spectrum width
using the novel perturbation analysis technique based on an integral
representation in the spectral domain. The stable soliton acquires spectral
modulation that follows the associated index of refraction of the absorber. The
model can be applied to ordinary soliton propagation and to an absorber inside
a passively modelocked laser. In the latter case, a comparison with water vapor
absorption in a femtosecond Cr:ZnSe laser yields a very good agreement with
experiment. Compared to the conventional absorption measurement in a cell of
the same length, the signal is increased by an order of magnitude. The obtained
analytical expressions allow further improving of the sensitivity and
spectroscopic accuracy making the soliton absorption spectroscopy a promising
novel measurement technique.Comment: 9 pages, 7 figures
Ultrasoft Quark Damping in Hot QCD
We determine the quark damping rates in the context of next-to-leading order
hard-thermal-loop summed perturbation of high-temperature QCD where weak
coupling is assumed. The quarks are ultrasoft. Three types of divergent
behavior are encountered: infrared, light-cone and at specific points
determined by the gluon energies. The infrared divergence persists and is
logarithmic whereas the two others are circumvented.Comment: 16 page
Infrared Behavior of High-Temperature QCD
The damping rate \gamma_t(p) of on-shell transverse gluons with ultrasoft
momentum p is calculated in the context of next-to-leading-order
hard-thermal-loop-summed perturbation of high-temperature QCD. It is obtained
in an expansion to second order in p. The first coefficient is recovered but
that of order p^2 is found divergent in the infrared. Divergences from
light-like momenta do also occur but are circumvented. Our result and method
are critically discussed, particularly regarding a Ward identity obtained in
the literature. When enforcing the equality between \gamma_t(0) and
\gamma_l(0), a rough estimate of the magnetic mass is obtained. Carrying a
similar calculation in the context of scalar quantum electrodynamics shows that
the early ultrasoft-momentum expansion we make has little to do with the
infrared sensitivity of the result.Comment: REVTEX4, 55 page
Invariant measure in hot gauge theories
We investigate properties of the invariant measure for the gauge field
in finite temperature gauge theories both on the lattice and in the continuum
theory. We have found the cancellation of the naive measure in both cases. The
result is quite general and holds at any finite temperature. We demonstrate,
however, that there is no cancellation at any temperature for the invariant
measure contribution understood as Z(N) symmetrical distribution of gauge field
configurations. The spontaneous breakdown of Z(N) global symmetry is entirely
due to the potential energy term of the gluonic interaction in the effective
potential. The effects of this measure on the effective action, mechanism of
confinement and condensation are discussed.Comment: Latex file, 65.5kB, no figure
Non-Abelian Collective Excitations in Unlinearized Quark-Gluon Plasma Media
We study the effect of unlinearized medium on the collective excitations in
quark-gluon plasma. We present two kinds of non-Abelian oscillation solutions
which respectively correspond to weakly and strongly nonlinear coupling of
field components in color space. We also show that the weakly nonlinear
solution is similar to Abelian-like one but has the frequency shift, which is
of order , from eigenfrequency.Comment: 7 page
How fast can the wall move? A study of the electroweak phase transition dynamics
We consider the dynamics of bubble growth in the Minimal Standard Model at
the electroweak phase transition and determine the shape and the velocity of
the phase boundary, or bubble wall. We show that in the semi-classical
approximation the friction on the wall arises from the deviation of massive
particle populations from thermal equilibrium. We treat these with Boltzmann
equations in a fluid approximation. This approximation is reasonable for the
top quarks and the light species while it underestimates the friction from the
infrared bosons and Higgs particles. We use the two-loop finite temperature
effective potential and find a subsonic bubble wall for the whole range of
Higgs masses GeV. The result is weakly dependent on : the wall
velocity falls in the range , while the wall thickness is
in the range . The wall is thicker than the phase equilibrium
value because out of equilibrium particles exert more friction on the back than
on the base of a moving wall. We also consider the effect of an infrared gauge
condensate which may exist in the symmetric phase; modelling it simplemindedly,
we find that the wall may become supersonic, but not ultrarelativistic.Comment: 42 pages, plain latex, with three figures. Minor editing August 1 (we
figured out how to do analytically some integrals we previously did
numerically, made corresponding (slight) changes to numerical results, and
corrected some typos.
Advances in perturbative thermal field theory
The progress of the last decade in perturbative quantum field theory at high
temperature and density made possible by the use of effective field theories
and hard-thermal/dense-loop resummations in ultrarelativistic gauge theories is
reviewed. The relevant methods are discussed in field theoretical models from
simple scalar theories to non-Abelian gauge theories including gravity. In the
simpler models, the aim is to give a pedagogical account of some of the
relevant problems and their resolution, while in the more complicated but also
more interesting models such as quantum chromodynamics, a summary of the
results obtained so far are given together with references to a few most recent
developments and open problems.Comment: 84 pages, 18 figues, review article submitted to Reports on Progress
in Physics; v2, v3: minor additions and corrections, more reference
Phase of the Wilson Line at High Temperature in the Standard Model
We compute the effective potential for the phase of the Wilson line at high
temperature in the standard model to one loop order. Besides the trivial vacua,
there are metastable states in the direction of hypercharge. Assuming
that the universe starts out in such a metastable state at the Planck scale, it
easily persists to the time of the electroweak phase transition, which then
proceeds by an unusual mechanism. All remnants of the metastable state
evaporate about the time of the phase transition.Comment: 4 pages in ReVTeX plus 1 figure; Columbia Univ. preprint CU-TP-63
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