Stars as Laboratories for Fundamental Physics - MPP Theory Group

Anomalous Stellar Energy Losses Bounded by Observations 81
Fig. 2.24. Average values of ρ n and T n for the HB star model of Fig. 2.4
where ρ 4 = ρ/10 4 g cm −3 and T 8 = T/10 8 K.
core I find ⟨T 7 8 /ρ 4 ⟩ ≈ 0.3 which leads to ϵ ≈ g 2 10 30 erg g −1 s −1 . Thus,
for g 10 = 1 one concludes that the helium-burning lifetime should be
reduced by a factor 80/(80 + 30) = 0.7.
This result may be compared with numerical evolution sequences
for 1.3 M ⊙ stars with an initial helium abundance of 25% and a metallicity
of Z = 0.02 (Raffelt and Dearborn 1987). The helium-burning
lifetime was found to be 1.2×10 8 yr which was modified to 0.7×10 8 yr
for g 10 = 1. This means that the axion losses on the HB led to a t He
reduction by a factor 0.6, in good agreement with the analytic estimate.
This comparison corroborates that the analytic criterion represents the
claimed impact of a novel energy loss on the helium-burning lifetime
with a reasonable precision.
Equation (2.40) may now be applied to many different cases. An
overview over the most salient results is given in Tab. 2.5 where the
original references are given, and the sections of this book are indicated
where a more detailed discussion can be found. Apart from the
listed examples, the argument has also been applied to low-mass supersymmetric
particles (Fukugita and Sakai 1982; Bouquet and Vayonakis
1982; Ellis and Olive 1983). However, it is now thought that supersymmetric
particles, if they exist, are probably not light enough to be
produced in stars whence the interest in this case has waned.