Understand
We investigate the joint effect of the cosmological phase transitions, thermal light dark matter, and the lepton asymmetry on the big bang nucleosynthesis and cosmic microwave background.
- We find that all of them can modify the predictions of the effective number of neutrino species and primordial nucleosynthesis.
- In turn, we observe that: 1) the cosmological observations can exclude slow and strong phase transitions with strength even smaller than $\mathcal{O}(10^{-3}-10^{-2})$; 2) a much larger portion of dark matter mass region is excluded when the phase transition temperature is closer to 1 MeV; and 3) the magnitude of the non-vanishing neutrino lepton asymmetry is limited to be around $\mathcal{O}(10^{-2}-10^{-1})$ depending on the phase transition strength.
- These phase transitions can produce stochastic gravitational wave background to be probed by pulsar timing array experiments.