Limits on Neutrino-Neutrino Scattering in the Early Universe

By F. Cyr-Racine, K. Sigurdson. 2013

137 citations recorded by the source corpus.

In the standard model neutrinos are assumed to have streamed across the Universe since they last scattered when the standard-model plasma temperature was ∼MeV. The shear stress of free-streaming neutrinos imprints itself gravitationally on the cosmic microwave background (CMB) and makes the CMB a sensitive probe of neutrino scattering. Yet, the presence of nonstandard physics in the neutrino sector may alter this standard chronology and delay neutrino free streaming until a much later epoch. We use observations of the CMB to constrain the strength of neutrino self interactions G_(eff) and put limits on new physics in the neutrino sector from the early Universe. Within the context of conventional Λ CDM parameters cosmological data are compatible with G_(eff)≲1/(56 MeV)^2 and neutrino free streaming might be delayed until their temperature has cooled to as low as ∼25 eV. Intriguingly, we also find an alternative cosmology compatible with cosmological data in which neutrinos scatter off each other until z∼10^4 with a preferred interaction strength in a narrow region around G_(eff)≃1/(10 MeV)^2≃8.6×10^8G_F, where G_F is the Fermi constant. This distinct self-interacting neutrino cosmology is characterized by somewhat lower values of both the scalar spectral index and the amplitude of primordial fluctuations. While we phrase our discussion here in terms of a specific scenario, our constraints on the neutrino visibility function are very general.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/ffde1c536f250ad1610c2b900d981b3e93238254

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Citations in the corpus

CMB-S4 Science Case, Reference Design, and Project Plan (2019, background): “A radiation fluid whose fluctuations do not exceed the sound speed of the plasma [179, 180] could arise from large neutrino self-interactions [181, 182, 183, 184, 185], neutrino-dark sector interactions [186, 187], or dark radiation self-coupling [188, 189, 190].”
A tale of two modes: neutrino free-streaming in the early universe (2017, methodology): “[44], we find that the posterior is bimodal, with a first mode characterized by small values of the effective neutrino coupling constant and consistent with the standard ΛCDM paradigm, and a second mode characterized by large values of the effective coupling constant and corresponding to a cosmology”
The Atacama Cosmology Telescope: DR4 maps and cosmological parameters (2020, unknown): “Two examples are introducing a self-interaction between neutrinos that delays free-streaming until shortly before recombination [15, 78], or introducing a period of early dark energy soon before recombination [16, 79].”
Phases of new physics in the CMB (2015, background): “[30, 39–42]), in general, do not produce a phase shift (at least as long as the fluctuations are adiabatic and their sound speed is not larger than that of the photons).”