Super-Planckian excursions of the inflaton and quantum corrections
  Models of inflation with super-Planckian excursion seem well in agreement
with the recent observations of B- mode polarization in the cosmic microwave
background (CMB) radiation by the BICEP2 data. In this note, we highlight the
challenges faced by such models from ultraviolet (UV) completion. In
particular, we will discus radiative corrections to the inflaton Lagrangian and
to the gravitational sector. We will emphasize why we would require an UV
complete theory of gravity to tackle some of the issues for the super-Planckian
excursion. In particular, we will highlight how higher derivative terms in the
inflaton and gravity sectors cause problems from non-locality and ghosts, if
considered order by order, and thus prompt us to take into account infinite
series of such terms. We will also stress how the presence of a scale of new
physics below the Planck scale would make some of the UV related problems more
compelling and invalidate some of the remedies that have been proposed in the
literature. Finally, we will briefly speculate on possible ways of curing some
of the challenges.
