The Dilaton and Modified Gravity

TL;DR

This paper explores the dilaton field in modified gravity theories, demonstrating its potential role as dark energy and analyzing constraints from equivalence principle tests and effects on large-scale structure.

Contribution

It introduces a matter density-dependent effective potential for the dilaton with an exponential form, linking it to dark energy and structure formation in cosmology.

Findings

Dilaton can act as dark energy in cosmological models.

Constraints from equivalence principle tests limit dilaton coupling.

Dilaton influences large-scale structure growth and slip functions.

Abstract

We consider the dilaton in the strong string coupling limit and elaborate on the original idea of Damour and Polyakov whereby the dilaton coupling to matter has a minimum with a vanishing value at finite field-value. Combining this type of coupling with an exponential potential, the effective potential of the dilaton becomes matter density dependent. We study the background cosmology, showing that the dilaton can play the role of dark energy. We also analyse the constraints imposed by the absence of violation of the equivalence principle. Imposing these constraints and assuming that the dilaton plays the role of dark energy, we consider the consequences of the dilaton on large scale structures and in particular the behaviour of the slip functions and the growth index at low redshift.