Zach Weiner (Perimeter Institute)

10:00am Wednesday Oct 22, 2025
Webinar

Light neutrinos and dark forces

Among the numerous, extant hints of physics beyond the standard cosmological model, perhaps the most surprising is the incompatibility of observations with the neutrino masses expected from neutrino oscillations. In fact, current data seem to prefer excess structure and a deficit of matter at late times, both the opposite of what nonzero neutrino masses predict. I will assess the potential to explain these puzzles with an additional long-range force acting on dark matter, which one might expect to enhance structure growth. I will explain why scalar-mediated dark forces in fact only exacerbate $\Lambda$CDM’s underpredicted degree of CMB lensing. Their expansion-history effects, however, are favored by current baryon acoustic oscillation data and relax neutrino mass limits. The counterintuitive phenomenology of dark forces exemplifies the nuances in the interpretation of physical effects on cosmological observables; drawing upon these lessons and analytic insight, I will conclude by exploring how one might engineer nonminimal models that genuinely enhance structure growth.