The Low-Energy Frontier of Particle Physics

TL;DR

This paper discusses the theoretical motivation, experimental prospects, and current status of searching for weakly interacting sub-eV particles (WISPs), such as axions and hidden photons, which are predicted by theories beyond the Standard Model.

Contribution

It provides a comprehensive overview of the physics case and experimental efforts in exploring the low-energy frontier involving WISPs, highlighting recent developments and future directions.

Findings

WISPs can cause observable effects in light-based experiments.

Experimental searches have placed constraints on WISP properties.

The low-energy frontier offers promising avenues for discovering new physics.

Abstract

Most embeddings of the Standard Model into a more unified theory, in particular the ones based on supergravity or superstrings, predict the existence of a hidden sector of particles which have only very weak interactions with the visible sector Standard Model particles. Some of these exotic particle candidates (such as e.g. "axions", "axion-like particles" and "hidden U(1) gauge bosons") may be very light, with masses in the sub-eV range, and have very weak interactions with photons. Correspondingly, these very weakly interacting sub-eV particles (WISPs) may lead to observable effects in experiments (as well as in astrophysical and cosmological observations) searching for light shining through a wall, for changes in laser polarisation, for non-linear processes in large electromagnetic fields and for deviations from Coulomb's law. We present the physics case and a status report of this emerging low-energy frontier of fundamental physics.