Speaker
Description
Axion-like particles (ALPs) with flavour violating couplings could be produced via freeze-in from the decays and scatterings of heavy quarks in the hot early universe. In the right region of parameter space ($f_a\gtrsim 10^{9}$ GeV and $m_a\gtrsim 0.1$ MeV) this population of axions would be weakly interacting and stable for the lifetime of the universe; an interesting dark matter candidate. However, certain decays and scatterings are infrared divergent; for example, $b+g\to s+\text{ALP}$ has a $t$ channel singularity when the intermediate $s$ quark goes on shell. These divergences must be cancelled before the relic density can be calculated and further phenomenology of the model discussed. In this talk I will discuss how these infrared divergences can be approached, first at zero temperature using the KLN theorem and then at finite temperature inside the collision term of the Boltzmann equation. I will demonstrate that disconnected diagrams are necessary for the zero temperature cancellation, and virtual corrections involving the finite temperature gluon propagator are vital for the finite temperature cancellation.