292 research outputs found
Anomalous specific heat in ultradegenerate QED and QCD
We discuss the origin of the anomalous behavior of the
low-temperature entropy and specific heat in ultradegenerate QED and QCD and
report on a recent calculation which is complete to leading order in the
coupling and which contains an infinite series of anomalous terms involving
also fractional powers in . This result involves dynamical hard-dense-loop
resummation and interpolates between Debye screening effects at larger
temperatures and non-Fermi-liquid behavior from only dynamically screened
magnetic fields at low temperature.Comment: 5 pages, 3 figures, contribution to the Proceedings of Strong and
Electroweak Matter 2004 (SEWM04), Helsinki, Finland, 16-19 Jun 200
Non-Fermi-Liquid Specific Heat of Normal Degenerate Quark Matter
We compute the low-temperature behavior of the specific heat of normal
(non-color-superconducting) degenerate quark matter as well as that of an
ultradegenerate electron gas. Long-range magnetic interactions lead to
non-Fermi-liquid behavior with an anomalous leading term.
Depending on the thermodynamic potential used as starting point, this effect
appears as a consequence of the logarithmic singularity in the fermion
self-energy at the Fermi surface or directly as a contribution from the only
weakly screened quasistatic magnetic gauge bosons. We show that a calculation
of Boyanovsky and de Vega claiming the absence of a leading term
missed it by omitting vector boson contributions to the internal energy. Using
a formulation which collects all nonanalytic contributions in bosonic ring
diagrams, we systematically calculate corrections beyond the well-known
leading-log approximation. The higher-order terms of the low-temperature
expansion turn out to also involve fractional powers and we
explicitly determine their coefficients up to and including order as
well as the subsequent logarithmically enhanced term . We derive
also a hard-dense-loop resummed expression which contains the infinite series
of anomalous terms to leading order in the coupling and which we evaluate
numerically. At low temperatures, the resulting deviation of the specific heat
from its value in naive perturbation theory is significant in the case of
strongly coupled normal quark matter and thus of potential relevance for the
cooling rates of (proto-)neutron stars with a quark matter component.Comment: REVTEX, 26 pages, 5 postscript figures. v3: new chapter added which
performs a complete hard-dense-loop resummation, covering the infinite series
of anomalous terms and extending the range of applicability to all T << m
Perturbative QCD at non-zero chemical potential: Comparison with the large-Nf limit and apparent convergence
The perturbative three-loop result for the thermodynamic potential of QCD at
finite temperature and chemical potential as obtained in the framework of
dimensional reduction is compared with the exact result in the limit of large
flavor number. The apparent convergence of the former as well as possibilities
for optimization are investigated. Corresponding optimized results for full QCD
are given for the case of two massless quark flavors.Comment: REVTEX4, 4 pages, 3 color figures. v2: fig. 3 now includes also
lattice data for two-flavor QCD at nonzero chemical potentia
Comment on `Pressure of Hot QCD at large N_f'
It is argued why quasiparticle models can be useful to describe the
thermodynamics of hot QCD excluding, however, the case of a large number of
flavors, for which exact results have been calculated by Moore.Comment: 5 pages, 2 figures (version accepted for publication
Anomalous specific heat in high-density QED and QCD
Long-range quasi-static gauge-boson interactions lead to anomalous
(non-Fermi-liquid) behavior of the specific heat in the low-temperature limit
of an electron or quark gas with a leading term. We obtain
perturbative results beyond the leading log approximation and find that
dynamical screening gives rise to a low-temperature series involving also
anomalous fractional powers . We determine their coefficients in
perturbation theory up to and including order and compare with exact
numerical results obtained in the large- limit of QED and QCD.Comment: REVTEX4, 6 pages, 2 figures; v2: minor improvements, references
added; v3: factor of 2 error in the T^(7/3) coefficient corrected and plots
update
Phase diagram at finite temperature and quark density in the strong coupling region of lattice QCD for color SU(3)
We study the phase diagram of quark matter at finite temperature (T) and
chemical potential (mu) in the strong coupling region of lattice QCD for color
SU(3). Baryon has effects to extend the hadron phase to a larger mu direction
relative to Tc at low temperatures in the strong coupling limit. With the 1/g^2
corrections, Tc is found to decrease rapidly as g decreases, and the shape of
the phase diagram becomes closer to that expected in the real world.Comment: 4 pages, 4 figures. To appear in the proceedings of the 19th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions,
Shanghai, China, Nov. 14-20, 2006 (Quark Matter 2006
Comment on and Erratum to "Pressure of Hot QCD at Large N_f"
We repeat and correct the recent calculation of the thermodynamic potential
of hot QCD in the limit of large number N_f of fermions. The new result for the
thermal pressure turns out to agree significantly better with results obtained
from perturbation theory at small coupling. For large coupling, a nonmonotonic
behaviour is reproduced, but the pressure of the strongly coupled theory does
not exceed the free pressure as long as the Landau pole ambiguity remains
negligible numerically.Comment: 9 pages, 3 figures, JHEP3; v2: version accepted for publication in
JHEP (title changed, 1 footnote added, 1 reference updated, content otherwise
unchanged
Asymptotic thermal quark masses and the entropy of QCD in the large-N_f limit
We study the thermodynamics of QCD in the limit of large flavor number (N_f)
and test the proposal to resum the physics of hard thermal loops (HTL) through
a nonperturbative expression for the entropy obtained from a Phi-derivable
two-loop approximation. The fermionic contribution to the entropy involves a
full next-to-leading order evaluation of the asymptotic thermal quark mass,
which is non-local, and for which only a weighted average value was known
previously. For a natural choice of renormalization scale we find remarkably
good agreement of the next-to-leading-order HTL results for the fermion self
energy and in turn for the entropy with the respective exact large-N_f results
even at very large coupling.Comment: REVTEX, 31 pages, 16 figure
Ultra-strong laser pulses: streak-camera for gamma-rays via pair production and quantum radiative reaction
We show that a strong laser pulse combined with a strong x-ray pulse can be
employed in a detection scheme for characterizing high-energy -ray
pulses down to the zeptosecond timescale. The scheme employs streak imaging
technique built upon the high-energy process of electron-positron pair
production in vacuum through the collision of a test pulse with intense laser
pulses. The role of quantum radiation reaction in multiphoton Compton
scattering process and limitations imposed by it on the detection scheme are
examined
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
- …