Stars as Laboratories for Fundamental Physics - MPP Theory Group

The Energy-Loss Argument 17
Table 1.1. Initial helium abundance for solar models with axion losses.
g 10 Y initial δ x X c
0 0.274 0.00 0.362
10 0.266 0.16 0.307
15 0.256 0.32 0.292
20 0.241 0.51 0.245
25 0.224 0.65 0.151
Sect. 5.2. For the present discussion the axion losses represent some
generic energy-loss mechanism with a rate proportional to the square
of the axion-photon coupling strength g aγ .
Without exotic losses a presolar helium abundance of Y initial = 0.274
was needed to reproduce the present-day Sun. For several values of
g 10 ≡ g aγ /10 −10 GeV −1 Raffelt and Dearborn found the initial helium
values given in Tab. 1.1 necessary to produce the present-day luminosity.
The values for δ x in Tab. 1.1 are defined as in Eq. (1.15) with L x
the axion luminosity of the (perturbed) present-day solar model which
has L γ = L ⊙ . Also, the central hydrogen abundance X c of the presentday
model is given. For g 10 = 30, corresponding to δ x ≈ 0.75, no
present-day Sun could be constructed for any value of Y initial .
The primordial helium abundance is thought to be about 23%, and
the presolar abundance is certainly larger. Still, a value of δ x less than
about 0.5 is hard to exclude on the basis of this calculation. Therefore,
the approximate solar constraint remains δ x ∼ < 1
2 or L x ∼ < L ⊙ as found
from the analytic treatment in the previous section.
One may be able to obtain an interesting limit by considering the
oscillation frequencies of the solar pressure modes. Because of the excellent
agreement between standard solar models and the observed p-mode
frequencies there is little leeway for a modified solar structure and composition.
This method has been used to constrain a hypothetical time
variation of Newton’s constant (Sect. 15.2.3).
1.3.3 Radiative Energy Transfer
If novel particles are so weakly interacting that they escape freely from
the star once produced their role is that of a local energy sink. Neutrinos
are of that nature, except in supernova cores where they are
“trapped” for several seconds. One could imagine new particles with