Stars as Laboratories for Fundamental Physics - MPP Theory Group

192 Chapter 5
an optical cavity in a strong transverse magnetic field (Sect. 5.4.4).
The dotted line marks roughly the expected range of sensitivity of the
PVLAS experiment (Sect. 5.4.4).
The solar limit (Eq. 5.22) is based on the Primakoff energy loss and
the requirement that axions must not exceed the photon luminosity;
otherwise the Sun could not have reached its present-day age.
The HB-star limit (Eq. 5.23) comes from the requirement that these
objects do not spend their nuclear fuel so fast that their observable
number in globular clusters is reduced by more than a factor of ≈ 2.
The “axion line” refers to models where E/N = 8/3 or ξ = 1 in
Eq. (14.24).
For very low-mass bosons (m a ∼ < 10 −10 eV) the SN 1987A flux of
pseudoscalars would be efficiently converted into γ-rays, leading to a
limit g aγ ∼ < 10 −11 GeV −1 (Sect. 5.5.3).
Fig. 5.9. Bounds on the photon coupling g aγ as a function of m a for arbitrary
pseudoscalars; see the text for details. (Adapted from Cameron et al. 1993.)