CREX- and PREX-II-motivated relativistic interactions and their implications for the bulk properties of nuclear matter and neutron stars

The Neutron Skin of 48Ca and 208Pb: A Critical Analysis

“…In microscopic predictions, DU processes are more likely to open at a few to several times normal density (based on projections, since chiral EFT predictions cannot be extended to such high densities). Using PREX II constraints, the Urca threshold is found to be approximately 1.5ρ 0 or just above 0.2 fm −3 [45]. From Equation (23), the value of the symmetry energy at 1.5ρ 0 is then about 58 MeV, clearly indicating an unusually steep density dependence, taking the PREX II value of 38.1 ± 4.7 MeV at saturation.…”

“…In ref. [45], the authors develop different parametrizations of RMF models constrained by CREX results, PREX II results, or a combination of both, and report that the direct Urca threshold density decreases from 0.71 fm −3 to 0.21 fm −3 as the skin of 208 Pb increases from 0.13 fm to 0.28 fm, with expected implications for neutron star cooling processes. To the best of our knowledge, there is no evidence for rapid neutrino cooling via direct Urca for low-mass (low central density) neutron stars.…”