Fundamental constants and their variability in theories of High Energy Physics

TL;DR

This paper reviews the theoretical exploration of fundamental constants' values and potential variability within high energy physics, emphasizing unification theories and modifications of gravity to explain cosmological phenomena.

Contribution

It provides a comprehensive overview of the theoretical approaches to understanding the values and possible variations of fundamental constants in high energy physics.

Findings

Fundamental constants may vary over cosmological timescales.

Unification of interactions could explain constant values.

Modifications of gravity are linked to cosmological constant variations.

Abstract

The Standard Model of particle physics and the theory of General Relativity (GR) currently provide a good description of almost all phenomena of particle physics and gravitation that have received controlled experimental tests. However, the Standard Model contains many a priori variable parameters whose values, and whose apparent (near-)constancy, have yet to receive a convincing theoretical explanation. At the same time, GR may now require to be extended or altered at the largest length scales, to account for the recent apparent accelerated cosmological expansion. In this introductory review I present theoretical aspects of the search for explanations of the values and possible variations of fundamental ``constants'', focusing on the possibility of unification of interactions. I also relate cosmological variations to modifications of gravity both locally and cosmologically.