Updated constraints on non-standard neutrino interactions from Planck

Abstract

We provide updated bounds on non-standard neutrino interactions based on data from the Planck satellite as well as auxiliary cosmological measurements. Two types of models are studied - A Fermi-like 4-point interaction and an interaction mediated by a light pseudoscalar - and we show that these two models are representative of models in which neutrinos either decouple or recouple in the early Universe. Current cosmological data constrain the effective 4-point coupling to be $G_X\le {\left(0.06\mathrm{GeV}\right)}^{-2}$, corresponding to $G_X\le 2.5\times 10^7{G}_F$. For non-standard pseudoscalar interactions we set a limit on the diagonal elements of the dimensionless coupling matrix, $g_{ij}$, of $g_{ii}\le 1.2\times 10^{-7}$. For the off-diagonal elements which induce neutrino decay the bound is significantly stronger, corresponding to $g_{ij}\le 2.3\times 10^{-11}(m/0.05\mathrm{eV}{)}^{-2}$, or a lifetime constraint of $\tau \ge 1.2\times 10^9\mathrm{s}(m/0.05\mathrm{eV}{)}^3$. This is currently the strongest known bound on this particular type of neutrino decay. We finally note that extremely strong neutrino self-interactions which completely suppress anisotropic stress over all of cosmic history are very highly disfavored by current data ($\Delta {\chi }^2\sim 10^4$).

Comments: 22 pages, 9 figures. Version published in JCAP