Δ(1232) and nucleon spectral functions in hot hadronic matter

Modifications of Δ(1232) and nucleon spectral functions at finite temperature and baryon density are evaluated in terms of resonant scattering off thermal pions, as well as a renormalization of the vacuum Δ-width including vertex corrections. The interactions are based on effective Lagrangians of pions and baryon resonances, with underlying parameters (coupling constants and form factors) determined by the elastic πN scattering phase shift in the isobar channel, and by empirical decay branchings of excited resonances. Pion modifications are included via interactions in a pion gas, as well as standard Δ- and nucleon-hole excitations in nuclear matter. In hot hadronic matter, under conditions resembling thermal freezeout at the Relativistic Heavy-Ion Collider (RHIC), the Δ exhibits a significant broadening of ∼65 MeV together with a slight upward peak shift of 5-10 MeV, in qualitative agreement with preliminary data from the STAR Collaboration.