Better late than never: What comparing two models that delay cosmic neutrino free-streaming can tell us

Despite the best efforts of particle physicists, the true nature of neutrinos remains a mystery. Their feeble interaction strengths make directly measuring their properties phenomenally difficult, but cosmology offers another probe. In the radiation-dominated epoch, neutrinos make up over 40% of the energy density of the universe, meaning their interactions–including any nonstandard interactions–become cosmologically significant. In this talk, I will introduce two models that produce stronger neutrino self-interactions: one simple and one more complex. By comparing how these models fare when confronted with data, we can explore why this intriguing scenario with stronger neutrino interactions is allowed and work towards improving our neutrino models. By generalizing these conclusions, we can further add to our understanding of both the Hubble and Sigma-8 tensions, aiding in the work toward a single solution to the biggest problems in modern cosmology.