arXiv subjects

R. Rapp

Publications and source records attributed to R. Rapp.

130 records · Page 8Linked to original sources

arXiv1995

Thermal Properties of a Hot Pion Gas beyond the Quasiparticle Approximation

Within the Matsubara formalism we derive expressions for the pion self-energy and the two-pion propagator in a hot pion gas. These quantities are used to selfconsistently calculate the in-medium $ππ$ amplitude beyond the quasiparticle approximation (QPA). The results are shown to differ significantly from QPA-based calculations. We also examine the impact of chiral constraints on the $ππ$ interaction in a chirally improved version of the Jülich $ππ$ model.

nucl-th↗

arXiv1994

S-Wave Pion-Pion Correlations in Dense Nuclear Matter

The s-wave correlated $π$-$π$ strength distribution in cold nuclear matter is investigated. The in-medium single pions are renormalized by means of the usual p-wave couplings to nucleons and $Δ$'s. Two groups of models for the $π$-$π$ interaction are studied. The first one uses phenomenological models which reproduce the phase shifts but do not respect the soft-pion theorems. With increasing density a strong accumulation of strength in the subhreshold region is observed. Slightly above saturation density there even occurs an instability with respect to s-wave $π$-$π$ pair condensation. These effects are strongly moderated or disappear altogether if constraints from chiral symmetry are built into the $π$-$π$ interaction.

nucl-th↗

arXiv1993

Pion Properties in a Hot $ΠN Δ$ Gas

Based on a recent meson-exchange model for the vacuum $ππ$ interaction we compute selfconsistently the in-medium $ππ$ scattering amplitude and pion selfenergy in a hot $πNΔ$ gas. The contributions to the pion selfenergy are calculated from the $ππ$ T-matrix as well as from p-wave interaction with nucleons and thermally abundant $Δ$'s. Results are presented for two scenarios believed to be realized in the relativistic heavy ion collisions performed at the GSI-SIS and the CERN-SpS. Possible implications for the observed soft pion enhancement at both SIS and SpS are indicated.

nucl-th↗

arXiv1993

Selfconsistent Description of a Thermal Piongas

We examine a hot pion gas by including medium modifications of the two-body scattering amplitude as well as mean-field effects selfconsistently. In contrast to earlier calculations, the in-medium T-matrix is rather close to the free one while the mean-field potential agrees well with lowest-order estimates. We also discuss the validity of the quasiparticle approximation. It is found that it is reliable for temperatures up to $\sim 150$ MeV. Above this temperature off-shell effects in the pion selfenergy become important, especially if the pions are strongly out of chemical equilibrium.

nucl-th↗