Constraints on general second-order scalar-tensor models from gravitational Cherenkov radiation

TL;DR

This paper investigates how gravitational Cherenkov radiation constrains general second-order scalar-tensor theories, including specific models like purely kinetic coupled gravity and extended galileon, by analyzing tensor mode speeds.

Contribution

It demonstrates that gravitational Cherenkov radiation imposes strong constraints on the propagation speeds in these scalar-tensor models, limiting their viability.

Findings

Tensor mode speed can be less than light speed in these models.

Cherenkov radiation constraints significantly restrict model parameters.

Certain models are ruled out or tightly constrained by these effects.

Abstract

We demonstrate that the general second-order scalar-tensor theories, which have attracted attention as possible modified gravity models to explain the late time cosmic acceleration, could be strongly constrained from the argument of the gravitational Cherenkov radiation. To this end, we consider the purely kinetic coupled gravity and the extended galileon model. In these models, the propagation speed of tensor mode could be less than the speed of light, which puts very strong constraints from the gravitational Cherenkov radiation.