Realizing Scale-invariant Density Perturbations in Low-energy Effective String Theory

Abstract

We discuss the realization of inflation and resulting cosmological perturbations in the low-energy effective string theory. In order to obtain nearly scale-invariant spectra of density perturbations and a suppressed tensor-to-scalar ratio, it is generally necessary that the dilaton field $\varphi$ is effectively decoupled from gravity together with the existence of a slowly varying dilaton potential. We also study the effect of second-order corrections to the tree-level action which are the sum of a Gauss-Bonnet term coupled to $\varphi$ and a kinetic term $(\nabla \varphi {)}^4$. We find that it is possible to realize observationally supported spectra of scalar and tensor perturbations provided that the correction is dominated by the $(\nabla \varphi {)}^4$ term even in the absence of the dilaton potential. When the Gauss-Bonnet term is dominant, tensor perturbations exhibit violent negative instabilities on small-scales about a de Sitter background in spite of the fact that scale-invariant scalar perturbations can be achieved.

13 pages; v2: minor corrections, refs. added, version to appear in PRD

Cited by in corpus (12)

• Models of f(R) Cosmic Acceleration that Evade Solar-System Tests
• Effective Field Theory for Inflation
• Construction of cosmologically viable f(G) gravity models
• Matter density perturbations and effective gravitational constant in modified gravity models of dark energy
• Power spectra from an inflaton coupled to the Gauss-Bonnet term
• Gauss-Bonnet cosmologies: crossing the phantom divide and the transition from matter dominance to dark energy
• On the Stability of a class of Modified Gravitational Models
• UV stable, Lorentz-violating dark energy with transient phantom era
• String inspired explanation for the super-acceleration of our universe
• Some exact solutions with torsion in 5-D Einstein-Gauss-Bonnet gravity
• Homogeneous cosmologies in generalized modified gravity
• Gauss-Bonnet Term on Vacuum Decay