Critical enhancement of the in-medium nucleon-nucleon cross section at low temperatures

The in-medium nucleon-nucleon cross section is calculated starting from the thermodynamic T matrix at finite temperatures. The corresponding Bethe-Salpeter equation is solved using a separable representation of the Paris nucleon-nucleon potential. The energy-dependent in-medium N-N cross section at a given density shows a strong temperature dependence. Especially at low temperatures and low total momenta, the in-medium cross section is strongly modified by in-medium effects. In particular, with decreasing temperature an enhancement near the Fermi energy is observed. This enhancement can be discussed as a precursor of the superfluid phase transition in nuclear matter.