Probing CP Violation in Photon Self-Interactions with Cavities

TL;DR

This paper explores the potential to detect CP violation in photon self-interactions at low energies using superconducting cavities, proposing new experimental methods and analyzing bounds on related new physics models.

Contribution

It introduces a novel experimental approach to isolate CP-violating effects in photon interactions using superconducting cavities and provides sensitivity projections for detecting new physics.

Findings

Proposed a method to isolate CP-violating contributions in photon self-interactions.

Analyzed bounds on new physics scales from theoretical and experimental constraints.

Projected experimental sensitivity to CP-violating couplings of light particles.

Abstract

In this paper we study CP violation in photon self-interactions at low energy. These interactions, mediated by the effective operator $FFF\tilde{F}$, where ($\tilde F$) $F$ is the (dual) electromagnetic field strength, have yet to be directly probed experimentally. Possible sources for such interactions are weakly coupled light scalars with both scalar and pseudoscalar couplings to photons (for instance, complex Higgs-portal scalars or the relaxion), or new light fermions coupled to photons via dipole operators. We propose a method to isolate the CP-violating contribution to the photon self-interactions using Superconducting Radio-Frequency cavities and vacuum birefringence experiments. In addition, we consider several theoretical and experimental indirect bounds on the scale of new physics associated with the above effective operator, and present projections for the sensitivity of the proposed experiments to this scale. We also discuss the implications of these bounds on the CP-violating couplings of new light particles coupled to photons.