Finite-temperature relativistic nuclear field theory: an application to the dipole response

Elena Litvinova and Herlik Wibowo 2018 Phys. Rev. Lett.  121 082501

Nuclear response theory beyond the one-loop approximation is formulated for the case of finite temperature. For this purpose, the time blocking approximation to the time-dependent part of the in-medium nucleon-nucleon interaction amplitude is adopted for the thermal (imaginary-time) Green’s function formalism. We found that introducing a soft blocking, instead of a sharp blocking at zero temperature, brings the Bethe-Salpeter equation to a single-frequency variable equation also at finite temperatures. The method is implemented self-consistently in the framework of quantum hadrodynamics and designed to connect the high-energy scale of heavy mesons and the low-energy domain of nuclear medium polarization effects in a parameter-free way. In this framework, we investigate the temperature dependence of dipole spectra in the even-even nuclei $48\mathrm{Ca}$ and $100,120,132\mathrm{Sn}$ with a special focus on the giant dipole resonance’s width problem and on the low-energy dipole strength distribution.