Emission of Axions in strongly magnetized star

We show that the axion decay constant does not get any correction at any order by external magnetic fields. On the other hand, in the context of the Wilsonian effective action under external magnetic fields, the axial currents get a finite correction. We then calculate the effect of strong magnetic fields $B>{10}^{18}G$ on the axion-nucleon coupling and find that if $B\gtrsim 10^{20}~G$ in strongly magnetized neutron and white dwarf stars, the emission rate of axions is enhanced by several orders of magnitude.