Examining the Effects of Theoretical Uncertainties in Nuclear Physics on the Constraints on Axion-Like Particles.*

Axions are well-motivated theoretical particles first proposed to explain the observed smallness of the neutron electric dipole moment. They may also be the dark matter that we observe on astrophysical scales. More generally, axion-like particles (ALPs) can interact with other standard-model particles, potentially violating symmetries of the Standard Model. For a particular choice of interactions, ALPs can permit the violation of lepton flavor, turning a muon into an electron in a way that is otherwise forbidden. ALPs are defined by their mass and the interactions that they have with standard-model particles. The fact that we have not yet detected axions in either laboratory experiments or in observations of astrophysical systems places strict constraints on these properties.

 

If the ALP is heavier than a muon, then many of the astrophysical and laboratory constraints no longer apply. Heavy, flavor-violating ALPs can exist momentarily as a muon is captured onto an atomic nucleus and is converted to an electron. The fact that this process has not been observed, despite significant experimental efforts, gives insight into how the ALP may interact with the muon, the electron, and the quarks inside the nucleus. In these experiments, the nucleus is used as a laboratory, introducing complicated nuclear physics. The aim of our project is to understand how theoretical uncertainties stemming from this nuclear physics affect the constraints obtained from these experiments.