  Pseudo-Goldstone bosons couple with photons through a P and T violating
interaction of the form ${\cal {L_I}}=g_{a\gamma \gamma}~ a F\tilde F$. Strong
magnetic fields in rotating compact stars induce a non-zero ${\vec E}\cdot{\vec
B}$ outside the stellar surface which acts as a source for the pseudo-scalar
field. Pulsar signals propagating through this pseudo-scalar `hair' suffer a
differential time lag between the left and the right circularly polarised modes
because of the P and T violating pseudoscalar boson-photon interaction.
Determination of this time lag upto a microsecond accuracy can lead to a
measurment of (or rule out) pseudo-Goldstone boson-photon coupling upto $g_{a
\gamma \gamma}\leq 4.6 \times 10^{-9}~GeV^{-1}$.
