NEUTRINO GRAVITATIONAL REDSHIFT AND THE ELECTRON FRACTION ABOVE NASCENT NEUTRON-STARS

Neutrinos emitted from near the surface of the hot proto-neutron star produced by a supernova explosion may be subject to significant gravit ational redshift at late times. Electron antineutrinos (<(nu)over bar (e)>) decouple deeper in the gravitational potential well of the neutr on star than do the electron neutrinos (nu(e), so that the <(nu)over b ar (e)> experience a larger redshift effect than do the nu(e). We show how this differential redshift can increase the electron fraction Y-e in the neutrino-heated ejecta from the neutron star. Any r-process nu cleosynthesis originating in the neutrino-heated ejecta would require a low Y-e, implying that the differential redshift effect cannot be to o large. In rum, this effect may allow nucleosynthesis to probe the nu clear equation of state parameters which set the neutron star radius a nd surface density scale height at times of order t(pb) approximate to 10 s to 25 s after core bounce.