Bounds on axion parameters from supernova emission

Abstract

The strong CP problem and axion theory are introduced. The existing bounds on the axion mass m(_a) and decay constant F(_a) are reviewed along with the recent bounds which were derived as a result of the supernova SN1987A.Current supernova theory is described. The method of terrestrial detection of supernova neutrinos is outlined. The neutrino detections from SN1987A and their importance in confirming theoretical expectations are explained. The methods of obtaining axion constraints from the limits on their production in the newly born neutron star at the centre of a supernova axe described. Particular emphasis is placed on the process NN → NNa, which is known as axion-nucleon-nucleon bremsstrahlung. The process pp → ppπ(^0) is studied since this is similar to NN → NNa. One boson exchange (OBE) models of the inter-nucleon potential are employed. Although OBE Born approximation amplitudes give the right order of magnitude for σ(_pp→ppx0), a good fit to the data can not be obtained with these alone. Further study would be required to determine the best theoretical form for the pp pp → ppπ(^0) matrix element and thus the NN → NNa matrix element. Axion energy production rate in a nascent neutron star is studied. OBE models are used to give a representation for the NN -» NNa matrix element. Relativistic kinematics is employed. Errors in, and omissions from, the work of previous authors are discussed. It is concluded that, despite various theoretical deficiencies, previous estimates of axion emission rate were not unreasonable. The density dependence of the nucleon mass is briefly considered and it is concluded that large changes in the axion emission rate can result. Further study of this matter would-be useful.