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

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 3-graviton vertex function in thermal quantum gravity

The high temperature limit of the 3-graviton vertex function is studied in thermal quantum gravity, to one loop order. The leading ($T^4$) contributions arising from internal gravitons are calculated and shown to be twice the ones associated with internal scalar particles, in correspondence with the two helicity states of the graviton. The gauge invariance of this result follows in consequence of the Ward and Weyl identities obeyed by the thermal loops, which are verified explicitly.Comment: 19 pages, plain TeX, IFUSP/P-100

Optimal Renormalization-Group Improvement of R(s) via the Method of Characteristics

We discuss the application of the method of characteristics to the renormalization-group equation for the perturbative QCD series within the electron-positron annihilation cross-section. We demonstrate how one such renormalization-group improvement of this series is equivalent to a closed-form summation of the first four towers of renormalization-group accessible logarithms to all orders of perturbation theory

The graviton self-energy in thermal quantum gravity

We show generally that in thermal gravity, the one-particle irreducible 2-point function depends on the choice of the basic graviton fields. We derive the relevant properties of a physical graviton self-energy, which is independent of the parametrization of the graviton field. An explicit expression for the graviton self-energy at high-temperature is given to one-loop order.Comment: 13 pages, 2 figure

Thermal matter and radiation in a gravitational field

We study the one-loop contributions of matter and radiation to the gravitational polarization tensor at finite temperatures. Using the analytically continued imaginary-time formalism, the contribution of matter is explicitly given to next-to-leading ($T^2$) order. We obtain an exact form for the contribution of radiation fields, expressed in terms of generalized Riemann zeta functions. A general expression is derived for the physical polarization tensor, which is independent of the parametrization of graviton fields. We investigate the effective thermal masses associated with the normal modes of the corresponding graviton self-energy.Comment: 32 pages, IFUSP/P-107

The entropy of the QCD plasma

Self-consistent approximations in terms of fully dressed propagators provide a simple expression for the entropy of an ultrarelativistic plasma, which isolates the contribution of the elementary excitations as a leading contribution. Further approximations, whose validity is checked on a soluble model involving a scalar field, allow us to calculate the entropy of the QCD plasma. We obtain an accurate description of lattice data for purely gluonic QCD, down to temperatures of about twice the transition temperature.Comment: 12 pages, 3 figures, REVTEX (minor modifications

The Nonabelian Debye Mass at Next-to-Leading Order

It is shown that after a resummation of leading high-temperature contributions, a complete and gauge-independent result for the nonabelian Debye screening mass at next-to-leading order can be extracted from the static gluon propagator. In contrast to previous, incomplete results, the correction to the Debye mass is found to be logarithmically sensitive to the nonperturbative magnetic mass and positive, in accordance with recent high-statistics results from lattice calculations.Comment: 8 pages, REVTEX v3.0, BI-TP 93/42 (minor corrections in text and references

One-loop surface tensions of (supersymmetric) kink domain walls from dimensional regularization

We consider domain walls obtained by embedding the 1+1-dimensional $\phi^4$-kink in higher dimensions. We show that a suitably adapted dimensional regularization method avoids the intricacies found in other regularization schemes in both supersymmetric and non-supersymmetric theories. This method allows us to calculate the one-loop quantum mass of kinks and surface tensions of kink domain walls in a very simple manner, yielding a compact d-dimensional formula which reproduces many of the previous results in the literature. Among the new results is the nontrivial one-loop correction to the surface tension of a 2+1 dimensional N=1 supersymmetric kink domain wall with chiral domain-wall fermions.Comment: 23 pages, LATeX; v2: 25 pages, 2 references added, extended discussion of renormalization schemes which dispels apparent contradiction with previous result

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 $T\ln T^{-1}$ 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 $T\ln T^{-1}$ 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 $T^{(3+2n)/3}$ and we explicitly determine their coefficients up to and including order $T^{7/3}$ as well as the subsequent logarithmically enhanced term $T^3 \ln (c/T)$. 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