M. Dirks

Thermal photon production rate from nonequilibrium quantum field theory

In the framework of closed time path thermal field theory we investigate the production rate of hard photons from a QCD plasma away from equilibrium. Dynamical screening provides a finite rate for chemically nonequilibrated distributions of quarks and gluons just as it does in the equilibrium situation. Pinch singularities are shown to be absent in the real photon rate even away from equilibrium. {copyright} {ital 1997} {ital The American Physical Society}

Thermal dileptons from pi - rho interactions in a hot pion gas

The production of low mass dileptons from {pi}-{rho} interactions in a hot medium is studied. Applying finite temperature perturbation theory the dilepton rate is computed up to order g{sub {rho}}{sup 2}. For dilepton masses below the {rho} the two-body reactions {pi}{pi}{r_arrow}{rho}{gamma}{sup {asterisk}}, {pi}{rho}{r_arrow}{pi}{gamma}{sup {asterisk}}, and the decay process {rho}{r_arrow}{pi}{pi}{gamma}{sup {asterisk}} give significant contributions. Nonequilibrium contributions to the thermal rate are estimated, including the modification of the particle distribution function with a nonzero pion chemical potential. A comparison of the dilepton rate with the recent data measured in nucleus-nucleus collisions at CERN SPS energy by the CERES Collaboration is also performed. It is shown that the additional thermal dileptons from {pi}-{rho} interactions can partially account for the excess of the soft dilepton yield seen experimentally. {copyright} {ital 1997} {ital The American Physical Society}

Resonant decay of parity odd bubbles in hot hadronic matter

Abstract We investigate the decay of metastable states with broken CP-symmetry which have recently been proposed by Kharzeev, Pisarski and Tytgat to form in hot hadronic matter. We consider the efficiency of the amplification of the η ′-field via parametric resonance, taking the backreaction into account. For times of the order t ≈10 fm, we find a particle density of about 0.7/fm 3 and a correlation length of ξ max ≈2.4 fm. The corresponding momentum spectra show a non-thermal behaviour.

A Slavnov-Taylor identity and equality of damping rates for static transverse and longitudinal gluons in hot QCD

Abstract A Slavnov-Taylor identity is derived for the gluon polarization tensor in hot QCD. We evaluate its implications for damping of gluonic modes in the plasma. Applying the identity to next to the leading order in hard-thermal-loop resummed perturbation theory, we derive the expected equality of damping rates for static transverse and longitudinal (soft) gluons. This is of interest also in view of deviating recent reports of γ t ( p =0)≠ γ l ( p =0) based on a direct calculation of γ l ( p =0).

Anomalous Processes in Effective Chiral Theories at High Temperatures

We discuss chiral theories of constituent quarks interacting with bosons at high temperatures. In the chirally symmetric phase we demonstrate by applying functional methods the presence of effective anomalous couplings for, e.g., {pi}{sigma}{r_arrow}{gamma}{gamma}, {gamma}{r_arrow}{pi}{pi}{pi}{sigma}, {ital KK}{r_arrow}{pi}{pi}{pi}{sigma}, etc., as they have recently been discussed by Pisarski. {copyright} {ital 1996 The American Physical Society.}