Alleviating $H_0$ tension in scalar-tensor and bi-scalar-tensor theories

TL;DR

This paper explores scalar-tensor and bi-scalar-tensor gravity theories as potential solutions to the H_0 tension, demonstrating mechanisms that modify gravitational effects and dark energy behavior to reconcile local and cosmic measurements.

Contribution

It introduces specific models within scalar-tensor and bi-scalar-tensor theories that can alleviate the H_0 tension through unique late-time mechanisms.

Findings

Smaller effective Newton's constant at intermediate times.

Phantom behavior of dark-energy equation-of-state parameter.

Alleviation of H_0 tension in both classes of theories.

Abstract

We investigate scalar-tensor and bi-scalar-tensor modified theories of gravity that can alleviate the $H_0$ tension. In the first class of theories we show that choosing particular models with shift-symmetric friction term we are able to alleviate the tension by obtaining smaller effective Newton's constant at intermediate times, a feature that cannot be easily obtained in modified gravity. In the second class of theories, which involve two extra propagating degrees of freedom, we show that the $H_0$ tension can be alleviated, and the mechanism behind it is the phantom behavior of the effective dark-energy equation-of-state parameter. Hence, scalar-tensor and bi-scalar-tensor theories have the capability of alleviating $H_0$ tension with both known sufficient late-time mechanisms.