Description
Models with neutrino nonstandard interactions (NSI) have the potential to solve cosmological tensions and experimental anomalies. In this work, we focus on studying the cosmological implications of the neutrino NSI with a light hypothetical scalar particle. In the first part, we study the effects of the NSI induced neutrino effective mass due to coherent forward scattering processes. A large neutrino effective mass suppresses the neutrino production in the early Universe ultimately implying a smaller than expected effective number of relativistic species $N_{\rm eff}$. This permits us to set bounds on the NSI parameter space using BBN, for a scalar mass in the range $10^{-15} {\rm eV}< m_{\phi}< 10^{-5}{\rm eV}$, our neutrino-scalar coupling constraint is more restrictive than any previous result. In the second part, we study massive neutrino self-interactions with large-scale structure data. While our results are consistent with previous studies using light mediators, we find that including the neutrino mass, $\sum m_{\nu}$, into the analysis eases the now withstanding $H_0$ tension.
