Licentiate Thesis defense: Axionlike particles, quantum loops, and supernovae: The role of quantum loop corrections for astrophysical ALPs

In this thesis the quantum field theory and astrophysical phenomenology of axionlike particles (ALPs) are studied. The effective field theory of ALPs is reviewed with a special focus on quantum loops, the renormalization group equations, and the equivalent forms of the interaction between ALPs and fermions.

To study the phenomenology of ALPs, both as dark matter candidate in the first paper that this thesis is based on, and as they are produced in supernova explosions in the second paper, an effective coupling between ALPs and photons is defined. In this way, the full one-loop effect of ALP-electron interactions can straightforwardly be incorporated in phenomenological analyses.

It is pointed out that the effective coupling is different in decay and ALP-photon conversion processes. Importantly, the resulting loop-induced ALP-photon conversion rate does not vanish for ALPs much lighter than the electron, as was often stated in the literature.

With this field theoretical basis, it is pointed out in the first paper that the decay of ALPs into photons via quantum loops has severe consequences for direct detection searches of ALP dark matter. In a large part of the parameter space that these experiments are sensitive to, the ALP would either not be long-lived enough to be dark matter, or the x-rays or gamma-rays originating from the decays of the ALP relic density should have been observed by indirect detection searches. Hence, while more heavy and strongly interacting ALPs coupled to electrons cannot be dark matter, many relatively lighter and weaker interacting models are ruled out already by indirect detection constraints.

Furthermore, ALPs can be produced efficiently in supernovae even if they interact only very weakly. The absence of anomalous cooling in SN1987A constrains the ALP-photon and ALP-electron interactions. Similarly, since no gamma-rays arrived on earth directly after the observation of the neutrino burst of SN1987A, further constraints can be derived.

Using the effective loop-induced coupling, some of the strongest bounds on the coupling between electrons and ALPs in the keV and MeV mass range are calculated in the second paper. Additionally, some technical details of the calculation are discussed and improved.