UCLA

Nearly all of the particles discovered to date have Compton wavelengths that are much too small to mediate long-range forces between atoms. In the early Universe, prior to the formation of atoms, the size of the observable Universe was significantly smaller than today. This difference in scales allows particles with small Compton wavelengths to mediate forces in the earliest stages of the Universe. The forces that mediate attractive interactions between particles, such as Yukawa forces, are of particular interest in that era. Yukawa forces, unlike other particle interactions, are always attractive, and generally such forces are much stronger than gravity. The strength of these forces allows for the swift collection and clustering of heavy particles into structures, even during radiation domination. The same Yukawa forces facilitate the removal of energy and angular momentum from these newly formed halos through radiation of scalar particles. This process initiates rapid collapse of the over-dense regions formed by long-range forces. This early structure formation and collapse has a rich phenomenology and can potentially address many open questions in physics and cosmology.