In a simplified ALP model with flavor-violating e-μ couplings, constraints from Δa_e, μ→3e, and other processes limit the branching ratio of μ⁻e⁻→e⁻e⁻ in aluminum muonic atoms to O(10^{-20}), with resonant regions more suppressed.
Red giant bound on the axion - electron coupling revisited
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abstract
If axions or other low-mass pseudoscalars couple to electrons (``fine structure constant'' $\alpha_a$) they are emitted from red giant stars by the Compton process $\gamma+e\to e+a$ and by bremsstrahlung $e+(Z,A)\to (Z,A)+e+a$. We construct a simple analytic expression for the energy-loss rate for all conditions relevant for a red giant and include axion losses in evolutionary calculations from the main sequence to the helium flash. We find that $\alpha_a\lapprox0.5\mn(-26)$ or $m_a\lapprox 9\,\meV/\cos^2\beta$ lest the red giant core at helium ignition exceed its standard mass by more than $0.025\,\MM_\odot$, in conflict with observational evidence. Our bound is the most restrictive limit on $\alpha_a$, but it does not exclude the possibility that axion emission contributes significantly to the cooling of ZZ~Ceti stars such as G117--B15A for which the period decrease was recently measured.
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Derives bremsstrahlung production rates and T-dependent energy-loss scalings for leptophilic bosons in NS cores to enable coupling constraints from cooling data.
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Axion-like Particles and Lepton Flavor Violation in Muonic Atoms
In a simplified ALP model with flavor-violating e-μ couplings, constraints from Δa_e, μ→3e, and other processes limit the branching ratio of μ⁻e⁻→e⁻e⁻ in aluminum muonic atoms to O(10^{-20}), with resonant regions more suppressed.
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Production of Leptophilic Bosons in Ultradegenerate Relativistic Matter
Derives bremsstrahlung production rates and T-dependent energy-loss scalings for leptophilic bosons in NS cores to enable coupling constraints from cooling data.