BBN Constraints on Universally Coupled Ultralight Dark Matter

Ultralight scalar dark matter (DM) can gain an interaction to all massive Standard Model (SM) particles through a universal coupling. Such a coupling can modify the properties of said SM particles through the generation of an effective mass. Flambaum and Stadnik already exploited this effect in a similar model to constrain the DM phase space through its effect on Big Bang Nucleosynthesis (BBN). However there is also a back-reaction from SM to DM particles which modifies the DM mass. Due to the ultra low DM mass this effect, which has not been studied previously in the literature, can be substantial. By including this back-reaction in the DM evolution we derive new BBN constraints and find them to deviate significantly from those derived in previous work.