Precursor of Inflation

Abstract

We investigate a nonsingular initial state of the Universe which leads to inflation naturally. The model is described by a scalar field with a quadratic potential in Eddington-inspired Born-Infeld gravity. The curvature of this initial state is given by the mass scale of the scalar field, which is much smaller than the Planck scale. Therefore, in this model, quantum gravity is not necessary in understanding this preinflationary stage, no matter how large the energy density becomes. The initial state in this model evolves eventually to a long inflationary period which is similar to the usual chaotic inflation.

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

“…The MPS is known to be unstable under the global perturbation (zero-mode scalar perturbation) [2]. With a small perturbation, the Universe evolves to the near-MPS stage, and then enters into the intermediate stage, which is followed by an inflationary attractor stage.…”

“…In the maximal pressure state (MPS), the scale factor exhibits an exponential expansion of the Universe. The MPS is the past attractor from which all the evolution paths of the Universe originate [2]. At early times, the energy density is very high at the MPS (the magnitudes of the field ϕ and its velocity are very large).…”

“…[2]. The matter action is given by a e-mail: iycho@seoultech.ac.kr b e-mail: naveen.nkumars@gmail.com…”

Spectral indices in Eddington-inspired Born-Infeld inflation

“…[9]. After the Universe leaves the near-MPS stage, it enters into the intermediate stage followed by the attractor stage in which the inflationary feature is very similar to that of the chaotic inflation model in GR.…”

“…An inflation model in the EiBI theory of gravity, which naturally avoids addressing the quantum nature of gravity by construction, was developed only recently [9]. The model is based on a scalar field with a quadratic potential similar to the chaotic inflation model [2] in general relativity (GR).…”