  The central engine that drives gamma ray burst (GRB) explosions may derive
from the ability of electrons/positrons and nucleons to tap into the momentum
and energy from the large neutrino luminosity emitted by an accretion disk
surrounding a black hole. This transfer of momentum and energy occurs due to
neutrino absorption, scattering, and annihilation and the non-spherical
geometry of the source both increases the annihilation efficiency and, close to
the black hole, directs the momentum transfer towards the disk axis. We present
annihilation efficiencies and the momentum/energy transfers for a number of
accretion disk models and compute the critical densities of infalling material
below which the transfer of neutrino momentum/energy will lead to an explosion.
Models in which the neutrinos and antineutrinos become trapped within the disk
have noticeably different momentum and energy deposition structure compared to
thin disk models that may lead to significant differences in the explosion
dynamics.
