A Hypothesis on the Internal Structure of Primordial Black Holes: Selection of Degrees of Freedom as the Origin of Dark Matter

The hypothesis that primordial black holes (PBHs) constitute a significant fraction of dark matter (DM) is a fascinating possibility, though it faces strict observational constraints. We propose a new, complementary thesis: during the gravitational collapse of the early universe's dense plasma, which forms PBHs, a physical "distillation" process occurs. This process selects and filters fundamental degrees of freedom based on their coupling strength. Only the constituents that interact primarily through gravity (e.g., gravitons or graviton-like collective states) remain within the PBH's inner structure or in the resulting stable remnants. Other degrees of freedom (like quarks, leptons, or photons) are effectively expelled or confined to outer regions. This concept would explain the observed weakness of DM interactions at a fundamental level and strengthen the PBH-DM hypothesis by imbuing these objects with an intrinsically "dark" nature. We outline the measurable predictions that arise from this mechanism and propose concrete pathways to test this hypothesis.