We point out that stars in the mass window ~ 8-12 Msun can serve as sensitive probes of the axion-photon interaction, g_{Agammagamma}. Specifically, for these stars axion energy losses from the helium-burning core would shorten and eventually elimina
te the blue loop phase of the evolution. This would contradict observational data, since the blue loops are required, e.g., to account for the existence of Cepheid stars. Using the MESA stellar evolution code, modified to include the extra cooling, we conservatively find g_{Agammagamma} <~ 0.8 * 10^{-10} GeV^{-1}, which compares favorably with the existing bounds.
We study the radiative corrections to all Kl3 decay modes to leading non-trivial order in the chiral effective field theory, working with a fully inclusive prescription on real photon emission. We present new results for Kmu3 modes and update previou
s results on Ke3 modes. Our analysis provides important theoretical input for the extraction of the CKM element Vus from Kl3 decays.
