Probing the angle of birefringence due to long range axion hair from pulsars
Tanmay Kumar Poddar, Subhendra Mohanty
Abstract
Rotating neutron star or pulsar can be a possible source of pseudo Nambu Goldstone bosons or axions which can mediate long range axionic hair outside of the pulsar. When the electromagnetic radiation is emitted from a pulsar and passes through the long range axion hair, the axion rotates the polarization of the electromagnetic radiation and produces birefringence. We obtain the angle of birefringence due to this long range axionic hair as 0.42\ifmmode^\circ\else\textdegree\fi{}. This value is within the accuracy of measuring the linear polarization angle of pulsar light which is $\ensuremath{\le}1.0\ifmmode^\circ\else\textdegree\fi{}$. Our result continues to hold as long as the range of the axion hair (inverse of axion mass) is greater than the radius of the pulsar, i.e., ${m}_{a}<{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$ and the axion decay constant ${f}_{a}\ensuremath{\lesssim}\mathcal{O}({10}^{17}\text{ }\text{ }\mathrm{GeV})$.