Emergent Majorana Mass and Axion Couplings in Superfluids

Abstract

Axions (in the general sense) may acquire qualitatively new couplings inside superfluids. Their conventional couplings to fermions, in empty space, involve purely imaginary masses; the new couplings involve emergent Majorana masses. The possibility of weak links for axions, recently put forward, is analyzed, rejected, and replaced with a non-local analogue.