273 research outputs found
The pressure of deconfined QCD for all temperatures and quark chemical potentials
We present a new method for the evaluation of the perturbative expansion of
the QCD pressure which is valid at all values of the temperature and quark
chemical potentials in the deconfined phase and which we work out up to and
including order g^4 accuracy. Our calculation is manifestly four-dimensional
and purely diagrammatic -- and thus independent of any effective theory
descriptions of high temperature or high density QCD. In various limits, we
recover the known results of dimensional reduction and the HDL and HTL
resummation schemes, as well as the equation of state of zero-temperature quark
matter, thereby verifying their respective validity. To demonstrate the overlap
of the various regimes, we furthermore show how the predictions of dimensional
reduction and HDL resummed perturbation theory agree in the regime
T~\sqrt{g}*mu. At parametrically smaller temperatures T~g*mu, we find that the
dimensional reduction result agrees well with those of the nonstatic
resummations down to the remarkably low value T~0.2 m_D, where m_D is the Debye
mass at T=0. Beyond this, we see that only the latter methods connect smoothly
to the T=0 result of Freedman and McLerran, to which the leading small-T
corrections are given by the so-called non-Fermi-liquid terms, first obtained
through HDL resummations. Finally, we outline the extension of our method to
the next order, where it would include terms for the low-temperature entropy
and specific heats that are unknown at present.Comment: 45 pages, 21 figures; v2: minor corrections and clarifications,
references added; v3: Fig 16 added, version accepted for publication in PR
Fermi spectra and their gauge invariance in hot and dense Abelian and non-Abelian theories
The one-loop Fermi spectra (one-particle and collective ones) are found for
all momenta in the -approximation and their gauge invariance in hot and
dense Abelian and non-Abelian theories is studied. It is shown that the
one-particle spectrum, if the calculation accuracy is kept strictly, is gauge
invariant for all momenta and has two branches as the bare one. The collective
spectrum always has four branches which are gauge dependent including also
their |\q|=0 limit. The exception is the case for which this
spectrum is gauge invariant for all momenta as well.Comment: 16 pages, latex, no figure
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
Collective Excitations of Massive Dirac Particles in Hot and Dense Medium
The one-loop dispersion equation which defines the collective excitations of
the massive Dirac particles in hot and dense quark-gluon medium is obtained in
the high temperature limit for the case and solved explicitly for all
|\q| when . Four well-separated spectrum branches (quasi-particle and
quasi-hole excitations) are found and their behaviors for the small and large
|\q| are investigated. All calculations are performed using the temperature
Green function technique and fixing the Feynman gauge. The gauge dependency of
the spectra found are briefly discussed.Comment: 7 pages, latex, no figure
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
One-particle and collective electron spectra in hot and dense QED and their gauge dependence
The one-particle electron spectrum is found for hot and dense QED and its
properties are investigated in comparison with the collective spectrum. It is
shown that the one-particle spectrum (in any case its zero momentum limit) is
gauge invariant, but the collective spectrum, being qualitatively different, is
always gauge dependent. The exception is the case for which the
collective spectrum long wavelength limit demonstrates the gauge invariance as
well.Comment: 9 pages, latex, no figure
Soliton Generation and Picosecond Collapse in Solid-State Lasers with Semiconductor Saturable Absorber
Based on self - consistent field theory we study a soliton generation in cw
solid-state lasers with semiconductor saturable absorber. Various soliton
destabilizations, i.e. the switch from femtosecond to picosecond generation
(''picosecond collapse''), an automodulation regime, breakdown of soliton
generation and hysteresis behavior, are predicted.Comment: 14 pages, 6 Postscript figures, Te
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