Influence on Starobinsky inflation by other fields with large amplitude
  The Starobinsky model is one of the inflation models consistent with the
result of CMB observation by the Planck satellite. We consider the dynamics of
the Starobinsky inflation in the presence of another scalar field with a large
expectation value during inflation due to a negative Hubble-induced mass. We
find that it would be affected if the other field has an amplitude close to the
Planck scale. In this case, we may observe such effects on the Starobinsky
model by future CMB experiments.
