Stars as Laboratories for Fundamental Physics - MPP Theory Group

538 Chapter 14
With N f = 3 one finds
C p = −0.10 − 0.45 cos 2 β,
C n = −0.18 + 0.39 cos 2 β . (14.31)
In the KSVZ model and in other hadronic axion models C u = C d =
C s = 0 which yields
C p = −0.39,
C n = −0.04. (14.32)
In Fig. 14.4 these couplings are shown, for DFSZ axions as a function
of cos 2 β. They are all uncertain to within about ±0.05, but even then
C p and C n never seem to vanish simultaneously.
Fig. 14.4. Axion couplings to fermions according to Eqs. (14.28), (14.31),
and (14.32).
14.4 Astrophysical Axion Bounds
Because axions couple to nucleons, photons, and electrons it is easy
to translate the bounds on such couplings derived in previous chapters
of this book into bounds on the Peccei-Quinn scale or equivalently, on
the axion mass. A possible modification of the usual axion models by
the quantum gravity effects discussed in Sect. 14.2.4 is ignored for the
present discussion. 92
92 Barr and Seckel (1992) studied astrophysical axion bounds when quantum gravity
effects are taken seriously.