Kavli Affiliate: David N. Spergel
| First 5 Authors: Christina D. Kreisch, Minsu Park, Erminia Calabrese, Francis-Yan Cyr-Racine, Rui An
| Summary:
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 $Lambda$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
$2-3sigma$ level. As seen in the past, the preference shifts to $Lambda$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
$700 lesssim ell lesssim 1000$ 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.
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