Atacama Cosmology Telescope: The persistence of neutrino self-interaction in cosmological measurements
Christina D. Kreisch, Minsu Park, Erminia Calabrese, Francis-Yan Cyr-Racine, Rui An, J. Richard Bond, Olivier Doré, Jo Dunkley, Patricio A. Gallardo, Vera Gluscevic, J. Colin Hill, Adam D. Hincks, Mathew S. Madhavacheril, J. J. McMahon, Kavilan Moodley, Thomas W. Morris, F. Nati, Lyman A. Page, Bruce Partridge, Maria Salatino, Cristobál Sifón, David N. Spergel, Cristian Vargas, Edward J. Wollack
Abstract
We use data from the Atacama Cosmology Telescope (ACT) DR4 to search for the presence of neutrino self-interaction in the cosmic microwave background. Consistent with prior works, the posterior distributions we find are bimodal, with one mode consistent with $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ and one where neutrinos strongly self-interact. By combining ACT data with large-scale information from WMAP, we find that a delayed onset of neutrino free streaming caused by significantly strong neutrino self-interaction is compatible with these data at the $2\ensuremath{-}3\ensuremath{\sigma}$ level. As seen in the past, the preference shifts to $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ with the inclusion of Planck data. We determine that the preference for strong neutrino self-interaction is largely driven by angular scales corresponding to $700\ensuremath{\lesssim}\ensuremath{\ell}\ensuremath{\lesssim}1000$ in the ACT E-mode polarization data. This region is expected to be key to discriminate between neutrino self-interacting modes and will soon be probed with more sensitive data.