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 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 $0.42^\circ$. This result is independent of the rotational frequency, radius of the pulsar, mass of the axion, and axion photon coupling constant. This value is within the accuracy of measuring the linear polarization angle of pulsar light which is $\leq 1.0^\circ$. 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; $m_a<10^{-11}$eV and the axion decay constant $f_a\lesssim \mathcal{O}(10^{17}\rm{GeV})$.
Highlights
Axion was first introduced by Peccei and Quinn (PQ) (1977) to solve the strong CP problem [1,2,3,4]
The neutron electric dipole moment dn depends on a parameter θand from chiral perturbation theory, we can obtain dn ∼ 10−16θe:cm. θis related to the QCD θ angle by θ 1⁄4 θ þ arg detMq [5,6], where Mq is the quark mass matrix
To solve the strong CP problem, Peccei and Quinn postulated that θis not just a parameter but it is a dynamical field which is driven to zero by its own classical potential
Summary
Axion was first introduced by Peccei and Quinn (PQ) (1977) to solve the strong CP problem [1,2,3,4]. To solve the strong CP problem, Peccei and Quinn postulated that θis not just a parameter but it is a dynamical field (scaled by 1=fa to make it dimensionless) which is driven to zero by its own classical potential It is a pseudo Nambu Goldstone boson which arises due to spontaneous breaking of global Uð1Þ symmetry at a scale fa which is called the axion decay constant and explicitly breaks at ΛQCD due to nonperturbative QCD effects. These are the QCD axions which solve the strong CP problem. The ALP dark matter background rotates the cosmic microwave background modes which constrain the mass of the axion and axion photon coupling constant [44]. We use the units ħ 1⁄4 c 1⁄4 1 throughout the paper
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