Gravitino Problem in Minimal Supergravity Inflation
  We study non-thermal gravitino production in the minimal supergravity
inflation. In this minimal model utilizing orthogonal nilpotent superfields,
the particle spectrum includes only graviton, gravitino, inflaton, and
goldstino. We find that a substantial fraction of the cosmic energy density can
be transferred to the longitudinal gravitino due to non-trivial change of its
sound speed. This implies either a breakdown of the effective theory during
reheating or a serious gravitino problem.
