  We present three-dimensional hydrodynamic simulations of the evolution of
selfgravitating, thick accretion discs around hyperaccreting stellar-mass black
holes. The black hole-torus systems are considered to be remnants of compact
object mergers, in which case the disc is not fed by an external mass reservoir
and the accretion is non-stationary. Our models take into account viscous
dissipation, described by an alpha-law, a detailed equation of state for the
disc gas, and an approximate treatment of general relativistic effects on the
disc structure by using a pseudo-Newtonian potential for the black hole
including its possible rotation and spin-up during accretion. Magnetic fields
are ignored. The neutrino emission of the hot disc is treated by a
neutrino-trapping scheme, and the neutrino-antineutrino annihilation near the
disc is evaluated in a post-processing step. Our simulations show that the
neutrino emission and energy deposition by neutrino-antineutrino annihilation
increase sensitively with the disc mass, with the black hole spin in case of a
disc in corotation, and in particular with the alpha-viscosity. We find that
for sufficiently large alpha-viscosity neutrino-antineutrino annihilation can
be a viable energy source for gamma-ray bursts.
