Pseudoscalar versus pseudovector pion-nucleon couplings in the nucleonic axion bremsstrahlung rate of neutron-star matter

The difference between the pseudoscalar and pseudovector {π}N couplings are examined in the context of the nucleonic axion bremsstrahlung rate. With the pseudovector coupling, eight diagrams contribute to the matrix element for axion bremsstrahlung. A naive use of the pseudoscalar coupling for these eight diagrams, on the other hand, gives a different matrix element and overestimates the energy-loss rate of degenerate neutron-star matter via neutron-neutron axion bremsstrahlung typically by an order of magnitude.