Emergent Majorana Mass and Axion Couplings in Superfluids
  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. 
Frank Wilczek
hep-ph cond-mat.supr-con hep-th