Springer : Precision CMB constraints on eV-scale bosons coupled to neutrinos

Sandner, Stefan; Witte, Samuel J.; Escudero, Miguel

doi:10.1140/epjc/s10052-023-11864-6

Article
Report number	arXiv:2305.01692 ; IFIC/23-13 ; FTUV-23-0413.0599 ; CERN-TH-2023-073
Title	Precision CMB constraints on eV-scale bosons coupled to neutrinos
Author(s)	Sandner, Stefan (Valencia U., IFIC) ; Escudero, Miguel (CERN) ; Witte, Samuel J. (Amsterdam U. ; U. Amsterdam, GRAPPA ; ICC, Barcelona U.)
Publication	2023-08-09
Imprint	2023-05-02
Number of pages	19
Note	9 + 8 pages, 14 figures, added minor comment on Hubble tension, matches published version
In:	Eur. Phys. J. C 83 (2023) 709
DOI	10.1140/epjc/s10052-023-11864-6
Subject category	astro-ph.CO ; Astrophysics and Astronomy ; hep-ph ; Particle Physics - Phenomenology
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, $\nu\bar{\nu} \rightarrow X$, and suppress neutrino free streaming near recombination -- even for couplings as small as $\lambda_\nu \sim \mathcal{O}(10^{-13})$. 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_{\rm 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 $U(1)_{L_\mu-L_\tau}$ gauge boson, and find that they represent the leading constraints for masses $m_X\sim 1\, {\rm eV}$. 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.
Copyright/License	publication: © 2023-2024 The Author(s) (License: CC-BY-4.0), sponsored by SCOAP³ preprint: (License: CC BY 4.0)

$Parameter space for neutrino interactions with a scalar (\textit{left panel}) and vector (\textit{right panel}) boson $X$ with mass $m_X$. The bounds are interpreted within the singlet majoron model, where $\lambda_\nu = m_\nu/v_L$ and for a light $U(1)_{L_\mu-L_\tau}$ gauge boson, for which $\lambda_\nu \simeq g_{\mu-\tau}$, respectively. An analysis of Planck legacy data excludes blue regions with $3\sigma$ confidence. Grey regions represent current cosmological, astrophysical and laboratory constraints, see Section~\ref{sec:otherconstraints} for details. In pink we indicate constraints coming from the out-of-equilibrium decay of the new $X$ boson which apply if a primordial abundance was generated before BBN. We also indicate the region of parameter space which will be tested by the Simons Observatory. In particular, the region above the purple dashed-dotted line will be tested because the thermalization of the $X$ boson leads to an observable excess of $\Delta N_{\rm{eff}} \geq 0.1$. Finally, we also highlight in red the best fit region of parameter space for the scenario of the $X$ boson being of scalar type and interacting with one neutrino family, $N_{\rm int} = 1$. This region is of particular interest because it indicates that non-trivial neutrino interactions are statistically slightly preferred over $\Lambda$CDM.$ $\textit{Left:} Effective interaction rates at the background level (solid lines) as well as at the perturbation level (dashed lines) for different values of $K_{\rm{eff}}$. The scenario considered consists of all $3$ neutrinos interacting with the scalar type boson. \textit{Right:} Evolution of the normalized $X$ boson energy density for the same scenarios as before. For reference, we highlight in dashed the photon energy density.$ $\textit{Left:} Effective interaction rates at the background level (solid lines) as well as at the perturbation level (dashed lines) for different values of $K_{\rm{eff}}$. The scenario considered consists of all $3$ neutrinos interacting with the scalar type boson. \textit{Right:} Evolution of the normalized $X$ boson energy density for the same scenarios as before. For reference, we highlight in dashed the photon energy density.$ Show more plots

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Record created 2023-05-05, last modified 2024-09-13

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