Nuclear response in a finite-temperature relativistic framework

The present work formulates the nuclear response theory beyond the relativistic random-phase approximation for the case of finite temperature. We model a compound nucleus within the framework of the thermal relativistic mean-field theory, which describes the interaction between the Dirac nucleons and mesons at finite temperature. A single frequency variable Bethe-Salpeter equation for the nuclear response function is derived with the aid of the imaginary-time projection operator, which contains the Fermi-Dirac occupation numbers. This approach called finite temperature relativistic time blocking approximation is utilized numerically to calculate the monopole, dipole, and quadrupole responses of the neutron-rich ⁶⁸Ni nucleus for various temperatures. The discussion will focus on the evolution of the nuclear multipole responses and pygmy dipole resonance of the ⁶⁸Ni nucleus with temperature.