Speaker
Description
We investigate the effect of quantum loops on the theory of
axionlike particles (ALPs) coupled to electrons. Contrary to some statements in the
recent literature, the effective ALP-photon coupling induced by an electron loop
can be sizeable in the plasma of a supernova. We define a general effective
coupling that depends on the kinematics of the specific process in which an ALP
scatters, decays, or is produced. Using this effective coupling, it can be shown that
production of ALPs by loop processes is in fact slightly more efficient than the
respective tree-level processes in a numerical model of SN1987A. We update the
bound on $ g_{ae} $ imposed by the observed duration of the neutrino burst of
SN1987A. Moreover, we derive a new bound, which does not exist at tree-level for
ALPs only coupled to electrons, from the non-observation of gamma-rays from
ALP decays directly after the initial neutrino burst was observed in 1987. These are
the leading constraints on $ g_{ae} $ in the ALP-mass range of roughly 30 keV to
240 MeV. Using the effective coupling, we furthermore point out that ALP dark
matter coupled to electrons is not stable in the keV mass range due to
loop-induced decays into photons. Large parts of the parameter space that direct
detection experiments are sensitive to are therefore either (i) incompatible with the
assumption of ALPs being dark matter as their lifetime is shorter than the age of
the universe, or are (ii) already excluded by indirect detection searches for x-rays
and gamma-rays as products of ALP decays.
