Alleviating the <i>H</i>₀ Tension in Scalar–Tensor and Bi-Scalar–Tensor Theories

Abstract

Herein, we investigate scalar–tensor and bi-scalar–tensor modified theories of gravity that can alleviate the H0 tension. In the first class of theories, we show that by choosing particular models with a shift-symmetric friction term we are able to alleviate the tension by obtaining a 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 H0 tension can be alleviated, and the mechanism behind this is the phantom behavior of the effective dark-energy equation-of-state parameter. Hence, scalar–tensor and bi-scalar–tensor theories have the ability to alleviate the H0 tension with both known sufficient late-time mechanisms.

Keywords

• <i>H</i>₀ tension
• modified gravity
• Horndeski
• scalar-tensor
• bi-scalar theories
• generalized Galileon