349 research outputs found
Gluon Thermodynamics at Intermediate Coupling
We calculate the thermodynamic functions of Yang-Mills theory to three-loop
order using the hard-thermal-loop perturbation theory reorganization of finite
temperature quantum field theory. We show that at three-loop order
hard-thermal-loop perturbation theory is compatible with lattice results for
the pressure, energy density, and entropy down to temperatures T ~ 2 - 3 T_c.Comment: 4 pages, 3 figures; v2 - published version
Chiral transition in a magnetic field and at finite baryon density
We consider the quark-meson model with two quark flavors in a constant
external magnetic field at finite temperature and finite baryon
chemical potential . We calculate the full renormalized effective
potential to one-loop order in perturbation theory. We study the system in the
large- limit, where we treat the bosonic modes at tree level. It is shown
that the system exhibits dynamical chiral symmetry breaking, i. e. that an
arbitrarily weak magnetic field breaks chiral symmetry dynamically, in
agreement with earlier calculations using the NJL model. We study the influence
on the phase transition of the fermionic vacuum fluctuations. For strong
magnetic fields, and in the chiral limit, the transition
is first order in the entire plane if vacuum fluctuations are not
included and second order if they are included. At the physical point, the
transition is a crossover for with and without vacuum fluctuations.Comment: 11 pages. 5figs. V2: fixed a few typos and added refs. Submitted to
PRD. V3: Added refs and substantial revision of tex
Three-loop HTL Free Energy for QED
We calculate the free energy of a hot gas of electrons and photons to three
loops using the hard-thermal-loop perturbation theory reorganization of
finite-temperature perturbation theory. We calculate the free energy through
three loops by expanding in a power series in m_D/T, m_f/T, and e^2, where m_D
and m_f are thermal masses and e is the coupling constant. We demonstrate that
the hard-thermal-loop perturbation reorganization improves the convergence of
the successive approximations to the QED free energy at large coupling, e ~ 2.
The reorganization is gauge invariant by construction, and due to cancellation
among various contributions, we obtain a completely analytic result for the
resummed thermodynamic potential at three loops. Finally, we compare our result
with similar calculations that use the Phi-derivable approach.Comment: 23 pages, 10 figures; v3 - typos corrected, additional discussions of
systematics added; corresponds with published versio
Four-loop screened perturbation theory
We study the thermodynamics of massless phi-fourth theory using screened
perturbation theory. In this method, the perturbative expansion is reorganized
by adding and subtracting a thermal mass term in the Lagrangian. We calculate
the free energy through four loops expanding in a double power expansion in m/T
and g^2, where m is the thermal mass and g is the coupling constant. The
expansion is truncated at order g^7 and the loop expansion is shown to have
better convergence properties than the weak-coupling expansion. The free energy
at order g^6 involves the four-loop triangle sum-integral evaluated by Gynther,
Laine, Schroeder, Torrero, and Vuorinen using methods developed by Arnold and
Zhai. The evaluation of the free energy at order g^7 requires the evaluation of
a nontrivial three-loop sum-integral, which we calculate by the same methods.Comment: 34 pages, 6 figures, RevTe
The Equation of State for Dense QCD and Quark Stars
We calculate the equation of state for degenerate quark matter to leading
order in hard-dense-loop (HDL) perturbation theory. We solve the
Tolman-Oppenheimer-Volkov equations to obtain the mass-radius relation for
dense quark stars. Both the perturbative QCD and the HDL equations of state
have a large variation with respect to the renormalization scale for quark
chemical potential below 1 GeV which leads to large theoretical uncertainties
in the quark star mass-radius relation.Comment: 7 pages, 3 figure
Three-loop Phi-derivable Approximation in QED
In this paper we examine Phi-derivable approximations in QED. General
theorems tell us that the gauge dependence of the n-loop Phi-derivable
approximation shows up at order g^(2n) where g is the coupling constant. We
consider the gauge dependence of the two-loop Phi-derivable approximation to
the Debye mass and show that it is of order e^4 as expected. We solve the
three-loop Phi-derivable approximation in QED by expanding sum-integrals in
powers of e^2 and m/T, where m is the Debye mass which satisfies a variational
gap equation. The results for the pressure and the Debye mass are accurate to
order e^5.Comment: 10 pages, 5 figures. v2: typos corrected and references adde
- …