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.

• Received 1 May 2018
• Revised 11 July 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.082501