Neutrino self-interaction 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 BBN and laboratory experiments such as K-meson and tau decay, double-neutrino beta decay etc. In this talk, I will discuss the cosmology of flavor specific neutrino self-interaction where only one or two neutrino flavor states are self-interacting. Such flavor-specific interactions are less constrained by laboratory experiments. I will show that CMB and other cosmological dataset favors strong flavor specific neutrino self-interaction. I will talk about the feasibility of addressing the Hubble tension in this framework. In this context, I will briefly discuss another avenue to alleviate the Hubble tension by introducing additional dark radiation species having isocurvature primordial perturbation. I will show that cosmological data prefers a blue-tilt of the dark radiation isocurvature spectrum which gives rise to a larger value of the Hubble constant.
