The Muon Abundance In The Primordial Universe

Muon abundance is required for the understanding of several fundamental questions regarding properties of the primordial Universe. In this paper, we evaluate the production and decay rates of muons in the cosmic plasma as a function of temperature. This allows us to determine when exactly the muon abundance disappears. When the Universe cools below the temperature kT(disappear) approximate to 4:135 MeV, the muon decay rate overwhelms production rates and muons vanish quasi-instantaneously from the Universe. Interestingly, we show that at Tdisappear, the muon number is nearly equal to baryon abundance.