Massive neutrino self-interactions and the Hubble tension

Abstract We consider flavour independent neutrino self-interactions among massive neutrinos mediated by a heavy scalar against cosmological data. Such a model had previously shown to have potential in completely resolving the Hubble tension for the very strong interaction case with coupling strength ∼ 109 times the Fermi constant, by delaying the onset of neutrino free-streaming until matter-radiation equality. Our cosmological model consists of a total nine parameters which includes the six ACDM parameters and three parameters related to neutrinos: sum of neutrino masses (Σmν ), neutrino energy density (Neff ), and the effective coupling strength, log10 [GeffMeV2]. With the latest CMB data from the Planck 2018 data release as well as auxiliary data, we find that the region in parameter space with such strong interactions is still present in the posterior distribution. However, high-l polarisation data from the Planck 2018 release disfavours this strongly interacting mode even though it cannot yet be excluded. Our resuts show that the neutrino mass bounds obtained from cosmological data remain robust against when considering neutrino self-interactions. We also find that the high-l polarisation data also does not allow for high values of H 0 that can solve the current Hubble discrepancy, i.e. this model is not a viable solution to the same.