Sub-galactic dark forces can reopen the fermion DM mass window

A weak attractive interaction confined to dark matter can outweigh gravity over subgalactic distances. This talk studies its effects on collapse and stable bound structures when the force is screened beyond roughly kiloparsec scales. Delaying its onset until low cosmic density avoids early-Universe and galaxy-structure constraints. For fermionic matter, the additional attraction can support much lighter particles against degeneracy pressure; a density-triggered phase transition provides a concrete delayed-activation mechanism.