Bound on largest r <∼ 0.1 from sub-Planckian excursions of inflaton

Chatterjee, Arindam and Mazumdar, Anupam (2015) Bound on largest r <∼ 0.1 from sub-Planckian excursions of inflaton. Journal of Cosmology and Astroparticle Physics, 2015 (1): 31. ISSN 1475-7516

Abstract

In this paper we will discuss the range of large tensor to scalar ratio, r , obtainable from a sub-Planckian excursion of a single , slow roll driven inflaton field. In order to obtain a large r for such a scenario one has to depart from a monotonic evolution of the slow roll parameters in such a way that one still satisfies all the current constraints of \texttt{Planck}, such as the scalar amplitude, the tilt in the scalar power spectrum, running and running of the tilt close to the pivot scale. Since the slow roll parameters evolve non-monotonically, we will also consider the evolution of the power spectrum on the smallest scales, i.e. at ##IMG## [http://ej.iop.org/icons/Entities/calP.gif] {Script P} s ( k ~ 10 16 Mpc −1 ) ##IMG## [http://ej.iop.org/icons/Entities/lesssim.gif] {lesssim} 10 −2 , to make sure that the amplitude does not become too large. All these constraints tend to keep the tensor to scalar ratio, r ##IMG## [http://ej.iop.org/icons/Entities/lesssim.gif] {lesssim} 0.1. We scan three different kinds of potential for supersymmetric flat directions and obtain the benchmark points which satisfy all the constraints. We also show that it is possible to go beyond r ##IMG## [http://ej.iop.org/icons/Entities/gtrsim.gif] {gtrsim} 0.1 provided we relax the upper bound on the power spectrum on the smallest scales.