Alternative mechanisms to end the EMDE before BBN

Investigate the two non-thermal-inflation mechanisms for restoring Standard Model radiation domination prior to Big Bang Nucleosynthesis in the dissipative dark sector considered here: (i) enable decay of the dark electron X outside collapsed structures while maintaining stability inside due to a substantial chemical potential or binding energy per X particle, and (ii) introduce a heavier dark component c that dominates the energy density and later decays into Standard Model radiation with a hierarchy ρ_c ≫ ρ_X. Determine whether either mechanism consistently produces the required transition without disrupting virialized primordial dark halos.

Background

The paper requires the early Universe to return to Standard Model radiation domination before BBN despite an early matter-dominated era (EMDE) driven by heavy, dissipative dark matter. Three potential routes are outlined: (1) a thermal phase transition (the focus of this work), (2) decay of X outside but stability within collapsed structures due to chemical potential or binding energy, and (3) a two-component sector in which a heavy c particle decays to SM radiation.

Only the first mechanism is developed in the paper. Assessing the remaining two options is necessary to establish the robustness of the cosmological history and the survival of early-formed dark halos through the transition back to radiation domination.