Avoiding instabilities in antisymmetric tensor field driven inflation

Abstract

Models of inflation with antisymmetric tensor studied in the past are plagued with ghost instability even in an unperturbed FRW background. We show that it is possible to avoid ghosts in an unperturbed FRW background by considering the most general kinetic term for antisymmetric tensor field. The kinetic part acquires a new gauge symmetry violating term whose effect on perturbed modes is to prevent the appearance of nondynamical modes, and thus avoid ghosts. For completeness, we perform a check for gradient instability and derive the conditions for perturbations to be free of gradient instability. * sandeepa16@iiserb.ac.in † abhilash92@iiserb.ac.in ‡ sukanta@iiserb.ac.in

Gravitational waves from inflation with antisymmetric tensor field

“…For completeness, we generalized the analysis of background dynamics of the model first presented in Ref. [37,38] taking into account all nonminimal coupling terms upto linear order in curvature, and found the parameter space region within which stable de-Sitter solutions are expected (Fig. 2).…”

“…With this choice of g µν and B µν , the equations of motion appears similar to the case of scalar field inflation model. It should be noted that the gauge breaking kinetic term in the action (1) does not have any effect on the background dynamics [38]. The dynamics of this system is described by the Einstein's equation G µν = κT µν and the B µν field equation along with a constraint equation for conservation of energy momentum tensor(∇ µ T µν = 0).…”

“…A preliminary study of perturbations for this model was undertaken in Ref. [38], where all the calculations were done in a test frame in which the metric perturbations were ignored.…”

“…Specifically, the presence of nonminimal coupling terms with the Ricci scalar R and/or the Ricci tensor R µν is a sufficient condition for the existence of de-sitter solutions, thereby supporting inflation [37]. Furthermore, known ghost and gradient instabilities can be avoided at least for the perturbed modes of B µν (keeping the metric unperturbed) by incorporating a gauge symmetry breaking kinetic term into the action [38].…”

“…In this paper we extend our study of the cosmological perturbation theory of 2-form inflation starting with the inclusion of tensor perturbations to metric, usually referred to as the primordial gravitational waves, in the model prescribed in [38]. The availability of recent gravitational wave data coming from binary neutron star merger GW170817 and its associated electromagnetic counterparts, demands that the speed of propagation of gravitational waves be equal to the speed of light [39].…”