Self-interacting neutrinos as a solution to the Hubble tension?

Self-interaction among the neutrinos in the early Universe has been proposed as a solution to the Hubble tension, a discrepancy between the measured values of the Hubble constant from CMB and low-redshift data. However, flavor-universal neutrino self-interaction is highly constrained by Big Bang Nucleosynthesis and other laboratory experiments such as, tau and K-meson decay, double-neutrino beta decay etc. We study the cosmology when only one or two neutrino states are self-interacting. Such flavor-specific interactions are less constrained by the laboratory experiments. Lastly, we address the feasibility of resolving the Hubble tension within the framework of such flavor-specific neutrino self-interaction.