Consequences of a Cosmic Scalar with Kinetic Coupling to Curvature

TL;DR

This paper explores a scalar-tensor gravitational theory with kinetic coupling to curvature, revealing its implications for solar system physics, early universe inflation, and cosmic evolution, including potential singularities.

Contribution

It introduces a scalar-vector-tensor gravity model with kinetic coupling to Ricci curvature, analyzing its effects across different cosmological regimes.

Findings

Weak coupling yields solar system-like equations with preferred-frame effects.

Strong coupling can induce inflationary behavior in the early universe.

Without a potential, the model predicts a coasting expansion ending in a singularity.

Abstract

The classical gravitational theory of a scalar field with a gradient coupling to the Ricci tensor is examined. This is a scalar-vector-tensor gravitational theory, but in the case that the coupling is weak and the scalar evolves like a quintessence field on cosmological time scales, the field equations within the solar system are similar to a vector-tensor theory predicting tightly-constrained preferred-frame effects. In the early universe, it is shown that strong coupling effects can damp the evolution of the scalar field rolling down a potential to help drive an inflationary epoch. In the absence of a potential, the strong coupling effects drive a coasting expansion epoch which ultimately terminates in a sudden singularity.