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Stars as Laboratories for Fundamental Physics - MPP Theory Group

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Particles Interacting with Electrons and Baryons 111<br />

Tab. 3.1. Astrophysical bounds on the Yukawa coupling ga of pseudoscalars (axions) to electrons.<br />

Upper limit Astrophysical Dominant emission Detailed<br />

αa = g a/4π 2 observable process discussion<br />

1.7×10 −22 Solar age Bremsstrahlung (75%), Compton (25%) here<br />

e + X → X + e + a (X = e, p, 4 He)<br />

γ + e → e + a<br />

1.0×10 −26 Galactic age inferred from break Bremsstrahlung (degenerate) Sect. 2.2.4<br />

in white-dwarf luminosity function e + 12 C ( 16 O) → 12 C ( 16 O) + e + a<br />

similar Period decre<strong>as</strong>e in DAV star G117–B15A same Sect. 2.2.5<br />

1.6×10 −26 Helium-burning lifetime of Compton Sect. 3.2.6<br />

horizontal-branch stars γ + e → e + a<br />

0.5×10 −26 Core m<strong>as</strong>s at helium ignition in Bremsstrahlung (degenerate) Sect. 2.5.2<br />

low-m<strong>as</strong>s red giants e + A → A + e + a Sect. 3.5.5<br />

(A = 4 He, 12 C, 16 O)

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