Resumen
In ultra dense and hot regions realized in stellar core-collapse, neutrinos take a major role in the energy and momentum transports. We investigate the growth of the magnetorotational instability (MRI) in neutrino viscous media by using linear and nonlinear calculations. It is found from the local linear analysis that the neutrino viscosity can suppress the MRI in the regime of weak magnetic field ( B 10^14G). This suggests that MHD turbulence sustained by the MRI might not be driven efficiently in neutrino viscous media. Applying this result to a collapsar disk, which is known as the central engine of gamma-ray bursts (GRB), we find that the MRI can be suppressed only in its inner region. Based on this finding, a new evolutionary scenario of a collapsar disk, the ``Episodic Disk Accretion Model'' is proposed. Finally, we report our recent numerical study on the nonlinear evolution of the MRI in neutrino viscous media.
