Starobinsky-like inflation in dilaton-brane cosmology

John Ellis,Nick E Mavromatos,Dimitri V Nanopoulos

doi:10.1016/j.physletb.2014.04.014

Abstract

We discuss how Starobinsky-like inflation may emerge from dilaton dynamics in brane cosmology scenarios based on string theory, in which our universe is represented as a three-brane. The effective potential may acquire a constant term from a density of effectively point-like non-pertubative defects on the brane. Higher-genus corrections generate corrections to the effective potential that are exponentially damped at large field values, as in the Starobinsky model, but at a faster rate, leading to a smaller prediction for the tensor-to-scalar perturbation ratio r. This may be compensated partially by logarithmic deformations on the world-sheet due to recoil of the defects due to scattering by string matter on the brane, which tend to enhance the tensor-to-scalar ratio. Quantum fluctuations of the ensemble of D-brane defects during the inflationary period may also enhance the tensor-to-scalar ratio.

Highlights

We discuss how Starobinsky-like inflation may emerge from dilaton dynamics in brane cosmology scenarios based on string theory, in which our universe is represented as a three-brane
Higher-genus corrections generate corrections to the effective potential that are exponentially damped at large field values, as in the Starobinsky model, but at a faster rate, leading to a smaller prediction for the tensor-to-scalar perturbation ratio r
The Starobinsky model might appear not to contain any fundamental scalar field that could be the inflaton, it is conformally equivalent to ordinary Einstein gravity coupled to a scalar field with an effective potential that drives inflation [10]

Summary

Contents lists available at ScienceDirect

The presence of the brane was essential for ensuring the appropriate four-dimensional structures that lead to inflation in this scenario This brany Liouville model of inflation is consistent with the Planck data [11], but has more free parameters than the Starobinsky model, since it involves two fields: one scalar (dilaton) and one pseudoscalar (axion-like field). The branes provide a cosmological constant A that is non-perturbative in the string genus expansion, and independent of the Starobinsky inflaton field φ, which is identified (up to a minus sign) with the canonically-normalized) Liouville/dilaton of the closed-string multiplet in the Einstein frame, i.e., φ = −Φ, where Φ is the dilaton and the string coupling is gs = eΦ = e−φ In this sub-critical string approach, the generalized Starobinsky potential (6) arises from non-perturbative string theory contributions involving brane worlds of the form.

The coefficients and

Note added