Constraints from Inflation on Scalar-Tensor Gravity Theories

TL;DR

This paper demonstrates how inflationary perturbation spectra can be used to constrain parameters of general scalar-tensor gravity theories, including effects of multiple fields and non-adiabatic perturbations.

Contribution

It introduces a method to use inflationary spectra to place bounds on scalar-tensor gravity parameters, accounting for multi-field effects and non-adiabatic perturbations.

Findings

Perturbation spectra constrain scalar-tensor gravity parameters.

Super-horizon curvature perturbations may vary due to non-adiabatic effects.

Inflationary constraints are comparable to nucleosynthesis and post-Newtonian bounds.

Abstract

We show how observations of the perturbation spectra produced during inflation may be used to constrain the parameters of general scalar-tensor theories of gravity, which include both an inflaton and dilaton field. An interesting feature of these models is the possibility that the curvature perturbations on super-horizon scales may not be constant due to non-adiabatic perturbations of the two fields. Within a given model, the tilt and relative amplitude of the scalar and tensor perturbation spectra gives constraints on the parameters of the gravity theory, which may be comparable with those from primordial nucleosynthesis and post-Newtonian experiments.