Physics
Scientific paper
Oct 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987phrvd..36.2211r&link_type=abstract
Physical Review D (Particles and Fields), Volume 36, Issue 8, 15 October 1987, pp.2211-2225
Physics
110
Stellar Structure, Interiors, Evolution, Nucleosynthesis, Ages, Giant And Subgiant Stars, Elementary Particle Processes
Scientific paper
We consider in detail the effect of the emission of ``hadronic'' invisible axions (which do not couple to electrons) from the interior of stars on stellar evolution. To this end we calculate plasma emission rates for axions due to the Primakoff process for the full range of conditions encountered in a giant star. Much attention is paid to plasma, degeneracy, and screening effects. We reconsider the solar bound by evolving a 1.0 Msolar star to solar age and lowering the presolar helium abundance so as to obtain the correct present-day luminosity of the Sun. The previous bound on the axion-photon coupling of G9<~2.5 (corresponding to ma<~17 eV R where R is a model-dependent factor of order unity) is confirmed, where G9 is the coupling constant G in units of 10-9 GeV-1. We then follow the evolution of a 1.3Msolar star from zero age to the top of the giant branch. Helium ignites for all values of G consistent with the solar bound; however, the core mass, surface temperature, and luminosity at the helium flash exceed the standard values. The luminosity at the helium flash is larger than about twice the standard value unless G9<~0.3 (corresponding to ma<~2 eV R), in conflict with observational data, which are statistically weak, however. We find our most stringent limits from the helium-burning lifetime. In the absence of axion cooling we calculate a lifetime of 1.2×108 yr which corresponds well with the value 1.5×108 yr derived from the number of red giants in the ``clump'' of the open cluster M67 and with the value 1.3×108 yr derived from the number of such stars in the old galactic disk population. We obtain a conservative limit of G9<0.3 which, at saturation, results in a helium-burning lifetime an order of magnitude low. We believe that G9<~0.1 (ma<~0.7 eV R) is a reasonably safe limit which, if saturated, leads to a calculated helium-burning lifetime a factor of 2 below the observed value. Our results exclude the recently suggested possibility of detecting cosmic axions through their 2γ decay and probably the possibility of measuring the solar hadronic axion flux which, according to our bounds, must be less than 2×10-3 of the solar luminosity. There remains a narrow range of parameters (0.01<~G9<~0.1, ma<~10-4 eV) in which a recently proposed laboratory experiment might still measure axionlike particles.
Dearborn David S. P.
~Raffelt Georg G.
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