Precision CMB constraints on eV-scale bosons coupled to neutrinos

Abstract

The cosmic microwave background (CMB) has proven to be an invaluable tool for studying the properties and interactions of neutrinos, providing insight not only into the sum of neutrino masses but also the free streaming nature of neutrinos prior to recombination. The CMB is a particularly powerful probe of new eV-scale bosons interacting with neutrinos, as these particles can thermalize with neutrinos via the inverse decay process, $$\nu \bar{\nu } \rightarrow X$$ ν ν ¯ → X , and suppress neutrino free streaming near recombination – even for couplings as small as $$\lambda _{\nu } \sim {\mathcal {O}}(10^{-13})$$ λ ν ∼ O ( 10 - 13 ) . Here, we revisit CMB constraints on such bosons, improving upon a number of approximations previously adopted in the literature and generalizing the constraints to a broader class of models. This includes scenarios in which the boson is either spin-0 or spin-1, the number of interacting neutrinos is either $$N_{\textrm{int}} = 1,2 $$ N int = 1 , 2 or 3, and the case in which a primordial abundance of the species is present. We apply these bounds to well-motivated models, such as the singlet majoron model or a light $$U(1)_{L_{\mu }-L_{\tau }}$$ U ( 1 ) L μ - L τ gauge boson, and find that they represent the leading constraints for masses $$m_X\sim 1\, {\textrm{eV}}$$ m X ∼ 1 eV . Finally, we revisit the extent to which neutrino-philic bosons can ameliorate the Hubble tension, and find that recent improvements in the understanding of how such bosons damp neutrino free streaming reduces the previously found success of this proposal.

Review of Hubble tension solutions with new SH0ES and SPT-3G data

“…[5], both the ΛCDM+m e and Majoron models did pass the 3σ-compatibility test. According to this work, they no longer appear as plausible solutions, with the Majoron results being in accordance with the findings of [74]. The ΛCDM+m e +Ω K and EDE models barely pass our tests and with a worse tension level than in ref.…”

A cosmological sandwiched window for lepton-number breaking scale

“…Such effects have been studied in refs. [26][27][28][29][30] where the constraints of N eff from the CMB measurements have been applied to derive the upper bound of the majoron-neutrino coupling in terms of the majoron mass.…”

“…Therefore, we concentrate on f > 1 GeV. Also, it is worthwhile to mention that for a lighter majoron around the eV scale, the nonrelativistic decay could occur after the epochs of matter-radiation equality and recombination when effects on, e.g., the structure formation and the neutrino free-streaming become significant [29]. On the other hand, for a heavier majoron above the MeV scale, the decay channel to electron-positron pairs opens.…”

“…The constraints on the lepton-number breaking scale from N eff have been noticed for a while [26][27][28][29][30], mostly in a model-independent setup. In previous works, the primordial abundance of the majoron was usually neglected such that the majoron abundance was initialized via the effective interaction between the active neutrinos and the majoron.…”

Non-minimally coupled Natural Inflation: Palatini and Metric formalism with the recent BICEP/Keck

“…We refer the reader to e.g. Refs [42,[53][54][55][56][57][58][59][60][61]. for a more detailed discussion.…”