  In the past, the axion-nucleon coupling has been calculated in the framework
of SU(2) heavy baryon chiral perturbation theory up to third order in the
chiral power counting. Here, we extend these earlier studies to the case of
heavy baryon chiral perturbation theory with SU(3) flavor symmetry and derive
the axion coupling to the full SU(3) baryon octet, showing that the axion also
significantly couples to hyperons. As studies on dense nuclear matter suggest
the possible existence of hyperons in stellar objects such as neutron stars,
our results should have phenomenological implications related to the so-called
axion window.
