Abstract
The possibility of density isomers in nuclear matter, induced by pion condensation, is discussed with special regard to heavy-ion collisions. The equation of state of the combined system of baryons and pions is treated within the framework of the linear σ-model. In dense baryon matter, such as in colliding nuclei at high energies, the state with a non-zero value of the static pion field 〈π〉 might become energetically favorable due to the attractive p-wave pion-nucleon interaction. We present results for the shift, due to the pion condensation, of the free and internal energy and of the pressure at finite temperatures up to kBT ∼ 100 MeV. Repulsive short-range baryon-baryon correlations in the pion-like channel, Δ(1232) isobar admixtures to the nucleons as well as finite-range pion-baryon vertex cutoffs are taken into account. The influence of various “reference” equations of state — adjusted to the equilibrium properties of nuclear matter in the uncondensed phase — on the density isomerism is discussed. The results for the critical density ρc, above which pion condensation is expected, are compared with calculations based on the singularities of the pion propagator D(k, ρ, ω, T) in a dense medium.
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