Positronium decays with a dark Z and fermionic dark matter

We investigate the invisible decay of positronium to probe the fermionic light dark matter mediated by the dark Z boson. The invisible decay rate of positronium through weak interaction in the standard model is too small to be detected in the experiment. We show that it can be enhanced to be observed in the future if the dark matter is lighter than the electron in the dark Z model. We also compute the relic abundance of such light dark matter and discuss the big bang nucleosynthesis constraint with an alternative thermal history scenario.

Automated summary

We investigate the invisible decay of positronium to study the fermionic light dark matter mediated by the dark Z boson. The standard model predicts a very small invisible decay rate for positronium through weak interaction, making it undetectable in experiments. However, we demonstrate that this can be enhanced and observed in the future if the dark matter is lighter than the electron in the dark Z model. Additionally, we calculate the relic abundance of such light dark matter and discuss its implications on the big bang nucleosynthesis under an alternative thermal history scenario.