Neutrinos and Nucleosynthesis in Gamma‐Ray Burst Accretion Disks

We calculate the nuclear composition of matter in accretion disks surroundingstellar mass black holes as are thought to accompany gamma-ray bursts (GRBs).We follow a mass element in the accretion disk starting at the point of nucleardissociation and calculate the evolution of the electron fraction due toelectron, positron, electron neutrino and electron antineutrino captures. Wefind that the neutronization of the disk material by electron capture can bereversed by neutrino interactions in the inner regions of disks with accretionrates of 1 M_solar/s and higher. For these cases the inner disk regions areoptically thick to neutrinos, and so to estimate the emitted neutrino fluxes wefind the surface of last scattering for the neutrinos (the equivalent of theproto-neutron star neutrinosphere) for each optically thick disk model. We alsoestimate the influence of neutrino interactions on the neutron-to-proton ratioin outflows from GRB accretion disks, and find it can be significant even whenthe disk is optically thin to neutrinos.Comment: 19 pages, 18 figures references added, two figures modifie