On Shapiro time delay in massive scalar-tensor theories

TL;DR

This paper investigates how massive scalar-tensor theories affect the Shapiro time delay, providing new expressions and demonstrating potential observational differences from general relativity.

Contribution

It establishes a correspondence between the post-Newtonian parameter and null geodesics in massive scalar-tensor theories, and derives the first expression for Shapiro delay in hybrid f(R)-gravity.

Findings

Massive scalar-tensor theories predict distinguishable Shapiro delays from general relativity.

Derived the first formula for Shapiro time delay in hybrid f(R)-gravity.

Showed the equivalence between post-Newtonian parameter γ and null geodesic parameters.

Abstract

The problem of determining the post-Newtonian parameter $\gamma$ in massive scalar-tensor theories is considered. We demonstrate equivalent correspondence between the post-Newtonian parameter $\gamma$ and the parameter appearing in the equation of null geodysic in massive scalar-tensor theories. We show that massive scalar-tensor theories can be distinguished from general relativity based on the predictions of Shapiro time delay. All calculations are presented using hybrid metric-Palatini f(R)-gravity as an example. The expression for Shapiro time delay in hybrid f(R)-gravity is obtained for the first time.