Finite Larmor Radius Effects on Weakly Magnetized, Dilute Plasmas
  We investigate the stability properties of a hot, dilute and differentially
rotating weakly magnetized plasma which is believed to be found in the
interstellar medium of galaxies and protogalaxies and in the low-density
accretion flows around some giant black holes like the one in the Galactic
center. In the linear MHD regime, we consider the combined effects of
gyroviscosity and parallel viscosity on the magnetorotational instability. The
helical magnetic field is considered in the investigation. We show that the
gyroviscous effect and the pitch angles cause a powerful gyroviscous
instability. Furthermore, in most of the cases, plasma with the above mentioned
properties is unstable and the growth rates of the unstable modes are larger
than that of the magnetorotational instability.
