  We investigate stochastic particle acceleration in accretion flows. It is
believed that the magnetorotational instability (MRI) generates turbulence
inside accretion flows and that cosmic rays (CRs) are accelerated by the
turbulence. We calculate equations of motion for CRs in the turbulent fields
generated by MRI with the shearing box approximation without back reaction to
the field. The results show that the CRs randomly gain or lose their energies
through the interaction with the turbulent fields. The CRs diffuse in the
configuration space anisotropically: The diffusion coefficient in direction of
the unperturbed flow is about twenty times higher than the Bohm coefficient,
while those in the other directions are only a few times higher than the Bohm.
The momentum distribution is isotropic, and its evolution can be described by
the diffusion equation in momentum space where the diffusion coefficient is a
power-law function of the CR momentum. We show that the shear acceleration
efficiently works for energetic particles. We also cautiously note that in the
shearing box approximation, particles that cross the simulation box many times
along the radial direction suffer unphysical runaway acceleration by the
Lorentz transformation, which needs to be taken with special care.
