Cosmological impact of $\nu$DM interactions enhanced in narrow redshift ranges

The impact of dark matter-neutrino ($\nu$DM) interactions on cosmological perturbations has regained attention, spurred by indications of non-zero couplings from high-multipole cosmic microwave background data, weak lensing, and Lyman-$\alpha$ observations. We demonstrate that a similar observational preference is obtained if $\nu$DM interactions are primarily enhanced during a specific epoch, $z\sim ({10}^4-{10}^5)$, leading to $>3\sigma$ preference for a non-zero interaction in the combined Atacama Cosmology Telescope and cosmic shear data. This redshift-limited enhancement circumvents other cosmological and astrophysical bounds and can be achieved within a neutrino portal dark matter framework incorporating resonantly enhanced scattering rates.