  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.
