Search for Variations of Fundamental Constants

TL;DR

This paper reviews the theoretical motivation and observational efforts to detect possible variations in fundamental constants like alpha, mu, and G, which could indicate new physics beyond General Relativity.

Contribution

It provides a comprehensive overview of the scenarios predicting constant variations and summarizes current observational constraints and claims.

Findings

No definitive evidence of constant variations so far

Most constraints limit variations to very small or zero levels

Some claims of detection remain unconfirmed

Abstract

The possibility of variations of the values of fundamental constants is a phenomenon predicted by a number of scenarios beyond General Relativity. This can happen if ``our'' fundamental constants are not the actual constants of the fundamental theory and their value is instead determined, for example, by the background value of some new field or the size of extra dimensions. So far, most studies have been devoted to constrain possible temporal variations of the electromagnetic fine structure constant $\alpha$, the proton to electron mass ratio $\mu = m_p/m_e$, and the gravitational constant $G_{\rm N}$. Apart some claims of the detection of a temporal or spatial variation of $\alpha$ and $\mu$, so far there is no clear observational evidence of any variation of our fundamental constants.