Constraints on secret neutrino interactions after Planck
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, via Giuseppe Saragat 1, I-44122 Ferrara (Italy)
Neutrino interactions beyond the standard model of particle physics may affect the cosmological evolution and can be constrained through observations. We consider the possibility that neutrinos possess secret scalar or pseudoscalar interactions mediated by the Nambu-Goldstone boson of a still unknown spontaneously broken global U(1) symmetry, as in, e.g., Majoron models. In such scenarios, neutrinos still decouple at T≅ 1 MeV, but become tightly coupled again (''recouple'') at later stages of the cosmological evolution. We use available observations of the cosmic microwave background (CMB) anisotropies, including Planck 2013 and the joint BICEP2/Planck 2015 data, to derive constraints on the quantity γ{sub νν}{sup 4}, parameterizing the neutrino collision rate due to scalar or pseudoscalar interactions. We consider both a minimal extension of the standard ΛCDM model, and more complicated scenarios with extra relativistic degrees of freedom or non-vanishing tensor amplitude. For a wide range of dataset and model combinations, we find a typical constraint γ{sub νν}{sup 4} ∼< 0.9× 10{sup −27} (95% C.L.), implying an upper limit on the redshift z{sub νrec} of neutrino recoupling 0∼< 850, leaving open the possibility that the latter occured well before hydrogen recombination. In the framework of Majoron models, the upper limit on γ{sub νν} roughly translates on a constraint g ∼< 8.2× 10{sup −7} on the Majoron-neutrino coupling constant g. In general, the data show a weak (∼ 1σ) but intriguing preference for non-zero values of γ{sub νν}{sup 4}, with best fits in the range γ{sub νν}{sup 4} = (0.15–0.35)× 10{sup −27}, depending on the particular dataset. This is more evident when either high-resolution CMB observations from the ACT and SPT experiments are included, or the possibility of non-vanishing tensor modes is considered. In particular, for the minimal model ΛCDM+γ{sub νν} and including the Planck 2013, ACT and SPT data, we report γ{sub νν}{sup 4}=(0.44{sup +0.17}{sub −0.36})×10{sup −27} (0300 ∼< z{sub νrec} ∼< 550) at 68% confidence level.
- OSTI ID:
- 22525730
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2015, Issue 07; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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