Super-Planckian excursions of the inflaton and quantum corrections

Abstract

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.