Scalar perturbation produced at the pre-inflationary stage in Eddington-inspired Born–Infeld gravity

Abstract

We investigate the scalar perturbation produced at the pre-inflationary stage driven by a massive scalar field in Eddington-inspired Born-Infeld gravity. The scalar power spectrum exhibits a peculiar rise for low k-modes. The tensorto-scalar ratio can be significantly lowered compared with that in the standard chaotic inflation model in general relativity. This result is very affirmative considering the recent dispute on the detection of gravitational wave radiation between PLANCK and BICEP2.

Spectral indices in Eddington-inspired Born-Infeld inflation

“…In EiBI inflation, however, the value can be reduced, as investigated in Refs. [11][12][13]. From Eqs.…”

“…Both the weak-and strong-gravity results in our work are well within this bound, as discussed in Refs. [12,13]. One problem in EiBI gravity to be resolved is the surface singularity accompanied with a polytropic star [27], which arises in the similar pathology of Palatini f (R) gravity theory [28].…”

“…In studying the primordial perturbations [10][11][12][13], therefore, the initial perturbations are considered to be produced at the near-MPS stage. They are assumed to evolve adiabatically until the attractor stage, and to exit near the beginning of the attractor stage.…”

“…[11][12][13], the minimum-energy condition is imposed at the initial moment τ * of the perturbation production at the near-MPS stage [19]. Then the perturbations are assumed to evolve adiabatically through the intermediate stage at which the WKB solution is applied, and finally enter the attractor stage.…”

“…The primordial perturbations of the model were investigated in Refs. [10][11][12][13]. In these works, the power spectra of both the scalar and tensor perturbations were studied, and it was found that the tensor power spectrum can be suppressed significantly, while the scalar spectrum remains almost the same.…”