Probing an ultralight QCD axion with electromagnetic quadratic interaction

Understand

The axion-gluon coupling is the defining feature of the QCD axion.

• This feature induces additional and qualitatively different interactions of the axion with standard model particles -- quadratic couplings.
• Previously, hadronic quadratic couplings have been studied and experimental implications have been explored especially in the context of atomic spectroscopy and interferometry.
• We investigate additional quadratic couplings to the electromagnetic field and electron mass.