Interacting neutrinos in cosmology: exact description and constraints

Abstract

We consider the impact of neutrino self-interactions described by an effective four-fermion coupling on cosmological observations. Implementing the exact Boltzmann hierarchy for interacting neutrinos first derived in [arxiv:1409.1577] into the Boltzmann solver CLASS, we perform a detailed numerical analysis of the effects of the interaction on the cosmic microwave background (CMB) anisotropies, and compare our results with known approximations in the literature. While we find good agreement between our exact approach and the relaxation time approximation used in some recent studies, the popular $\left(c_{\text{eff}}^2,c_{\text{vis}}^2\right)$-parameterisation fails to reproduce the correct scale dependence of the CMB temperature power spectrum. We then proceed to derive constraints on the effective coupling constant $G_{\text{eff}}$ using currently available cosmological data via an MCMC analysis. Interestingly, our results reveal a bimodal posterior distribution, where one mode represents the standard $\Lambda$CDM limit with $G_{\mathrm{eff}}\lesssim 10^8{G}_{\mathrm{F}}$, and the other a scenario in which neutrinos self-interact with an effective coupling constant $G_{\mathrm{eff}}\simeq 3\times 10^9{G}_{\mathrm{F}}$.

25 pages, 11 figures; accepted for publication in JCAP

References in corpus (11)

• The Clustering of the SDSS DR7 Main Galaxy Sample I: A 4 per cent Distance Measure at z=0.15
• Is dark matter with long-range interactions a solution to all small-scale problems of ΛCDM cosmology?
• Cosmic neutrino cascades from secret neutrino interactions
• IceCube PeV-EeV Neutrinos and Secret Interactions of Neutrinos
• Limits on Majoron-emitting double-beta decays of Xe-136 in the KamLAND-Zen experiment
• Revising Limits on Neutrino-Majoron Couplings
• Natural Inflation: Consistency with Cosmic Microwave Background Observations of Planck and BICEP2
• Are cosmological neutrinos free-streaming?
• Dark Radiation and interacting scenarios
• Nonlinear dynamics from the relativistic Boltzmann equation in the Friedmann-Lemaître-Robertson-Walker spacetime
• Constraining Models of Neutrino Mass and Neutrino Interactions with the Planck Satellite

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