Dispersion Relations in Ultradegenerate Relativistic Plasmas

The propagation of excitation modes in a relativistic ultradegenerate plasma is modified by their interactions with the medium. These modifications can be computed by evaluating their on-shell self-energy, which gives (gauge-independent) dispersion relations. For modes with momentum close to the Fermi momentum, the one-loop fermion self-energy is dominated by a diagram with a soft photon in the loop. We find the one-loop dispersion relations for quasiparticles and antiquasiparticles, which behave differently as a consequence of their very different phase-space restrictions when they scatter with the electrons of the Fermi sea. In a relativistic system, the unscreened magnetic interactions spoil the normal Fermi liquid behavior of the plasma. For small values of the Fermi velocity, we recover the non-relativistic dispersion relations of condensed matter systems.Comment: 14 pages; some comments on the helicities of the particles added; accepted for publication in PR

Hard Thermal Loops in Chiral Perturbation Theory

It is shown how the hard thermal loop approximation can be used in chiral perturbation theory to study some thermal properties of Goldstone bosons. Hard thermal effects are first studied in the non-linear sigma model. Then those results are used to obtain the thermal corrections to the transverse and longitudinal gauge field masses in the electroweak theory in the limit of a strongly interacting Higgs boson.Comment: 7 pages; Talk given at the 5th International Workshop on Thermal Field Theories and their Applications, Regensburg (Germany), August 199

Differential Renormalization of a Yukawa Model with γ5\gamma_5

We present a two-loop computation of the beta functions and the anomalous dimensions of a $\gamma_5$-Yukawa model using differential renormalization. The calculation is carried out in coordinate space without modifying the space-time dimension and no ad-hoc prescription for $\gamma_5$ is needed. It is shown that this procedure is specially suited for theories involving $\gamma_5$, and it should be considered in analyzing chiral gauge theories.Comment: 13 pages, Latex, 3 figures upon request, NBI-HE-92-7

Fermion Damping Rate Effects in Cold Dense Matter

We review the non-Fermi or marginal liquid behavior of a relativistic QED plasma. In this medium a quasiparticle has a damping rate that depends linearly on the distance between its energy and the Fermi surface. We stress that this dependence is due to the long-range character of the magnetic interactions in the medium. Finally, we study how the quark damping rate modifies the gap equation of color superconductivity, reducing the value of the gap at the Fermi surface.Comment: 5 pages, Talk given at Strong and Electroweak Matter 2000, 14-17 June, Marseill

QCD Effective Actions at High Temperature and the Quasiparticle Picture

Transport theory is an efficient approach to derive an effective theory for the soft modes of QCD at high temperature. It is known that the leading order operators of this theory can be obtained from (semi-classical) kinetic equations of quasiparticles carrying classical or quantum color charges. Higher order operators can also be obtained. Discrepancy between these quasiparticle models starts for dimension 4 operators, which converge in the limit of high dimensional color representations. These quasiparticle models are reviewed and compared.Comment: 5 pages, talk given at SEWM2002, Heidelberg, October 200

Transport Coefficients in Color Superconducting Quark Matter

Transport coefficients of dense quark matter are needed to study properties of compact stars. They can tell us about the cooling, vibrational and rotational properties of the star. We report below a computation of the shear viscosity in the CFL phase at low temperature T. CFL quark matter behaves as a superfluid, and at low T its transport properties are dominated by the collisions of superfluid phonons.Comment: 5 pages; talk given in Strong and Electroweak Matter (SEWM 2004), Helsini, Finland, June 200

Jet-induced gauge field instabilities in the quark-gluon plasma

We discuss the properties of the collective modes of a system composed by a thermalized quark-gluon plasma traversed by a relativistic jet of partons. The transport equations obeyed by the components of the plasma and of the jet are studied in the Vlasov approximation. Assuming that the partons in the jet can be described with a tsunami-like distribution function we derive the expressions of the dispersion law of the collective modes. Then the behavior of the unstable gauge modes of the system is analyzed for various values of the velocity of the jet, of the momentum of the collective modes and of the angle between these two quantities. We find that the most unstable modes are those with momentum orthogonal to the velocity of the jet, and the effect is stronger for ultrarelativistic jet velocities. Our results suggest a new possible collective mechanism for the description of the jet quenching phenomena in heavy ion collisions.Comment: 7 pages; invited talk at the YITP symposium on "Fundamental Problems in Hot and/or dense QCD", Kyoto, Japan, 3-6 March 200