Vector inflation by kinetic coupled gravity

Abstract

Vector inflation is a newly established model where inflation is driven by nonminimally coupled massive vector fields with a potential term. This model is similar to the model of chaotic inflation with scalar fields, except that for vector fields the isotropy of expansion is achieved either by considering a triplet of orthogonal vector fields or N randomly oriented independent vector fields. We introduce a new model of vector inflation where the vector field has no potential term and is nonminimally coupled to gravity through the kinetic term. This model shows that vector inflation without a potential term is possible and helps to avoid the fine tuning problem in inflationary models having a potential. The nonminimal coupling is established by introducing the Einstein tensor besides the metric tensor within the kinetic term of the vector field. A perturbation analysis is performed to confront the inflation under discussion with Planck and BICEP2 results.