Addendum: Towards a precision calculation of the effective number of neutrinos N
               <sub>eff</sub> in the Standard Model: the QED equation of state

Bennett, Jack L.; Buldgen, Gilles; Drewes, Marco; Wong, Yvonne Y. Y.

doi:10.1088/1475-7516/2021/03/a01

Cited by 15 publications

(36 citation statements)

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“…with the energy density in photons ρ γ and active plus sterile neutrinos (ρ ν + ρ s ). They can be computed from the integrated distribution functions, and for negligible contributions from the sterile we recover the standard value N 3ν eff = 3.043−3.045 [78,[80][81][82]84]. On the other hand, if the mixing parameters are sufficiently large, there is time for neutrino oscillations to fully bring the fourth neutrino to equilibrium with the active flavors.…”

Section: Light Sterile Neutrinos In Cosmologysupporting

confidence: 54%

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Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches

Hagstotz,

de Salas,

Gariazzo

et al. 2020

Preprint

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We provide a consistent framework to set limits on properties of light sterile neutrinos coupled to all three active neutrinos using a combination of the latest cosmological data and terrestrial measurements from oscillations, β-decay and neutrinoless double-β decay (0νββ) experiments. We directly constrain the full 3 + 1 active-sterile mixing matrix elements |U α4 | 2 , with α ∈ (e, µ, τ ), and the mass-squared splitting ∆m 2 41 ≡ m 2 4 − m 2 1 . We find that results for a 3 + 1 case differ from previously studied 1 + 1 scenarios where the sterile is only coupled to one of the neutrinos, which is largely explained by parameter space volume effects. Limits on the mass splitting and the mixing matrix elements are currently dominated by the cosmological data sets. The exact results are slightly prior dependent, but we reliably find all matrix elements to be constrained below |U α4 | 2 10 −3 .Short-baseline neutrino oscillation hints in favor of eV-scale sterile neutrinos are in serious tension with these bounds, irrespective of prior assumptions. We also translate the bounds from the cosmological analysis into constraints on the parameters probed by laboratory searches, such as m β or m ββ , the effective mass parameters probed by β-decay and 0νββ searches, respectively. When allowing for mixing with a light sterile neutrino, cosmology leads to upper bounds of m β < 0.09 eV and m ββ < 0.07 eV at 95% C.L, more stringent than the limits from current laboratory experiments.

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Section: Light Sterile Neutrinos In Cosmologysupporting

confidence: 54%

“…The final momentum distribution function for the active neutrinos is very close, but not exactly equal, to a Fermi-Dirac shape with the neutrino temperature T ν (see e.g. [78][79][80][81][82]).…”

Section: Light Sterile Neutrinos In Cosmologymentioning

confidence: 84%

Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches

Hagstotz,

de Salas,

Gariazzo

et al. 2020

Preprint

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“…3 Given that the reaction rate which keeps the neutrinos in thermal equilibrium scales as T 5 , it is a good approximation to assume that neutrino decoupling happens instantaneously when T 5 /H reaches the value it has at neutrino decoupling only considering the SM degrees of freedom, i.e. T 5 νd /H(T νd ) 1.62 × 10 −10 GeV 4 taking T SM νd 1.4 MeV [37,38]. After decoupling, the neutrino temperature T ν redshifts as 1/R.…”

Section: Evolution Of the Decaying Particle φmentioning

confidence: 99%

Updated BBN constraints on electromagnetic decays of MeV-scale particles

Depta¹,

Hufnagel

Schmidt-Hoberg³

2021

J. Cosmol. Astropart. Phys.

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In this work, we revise and update model-independent constraints from Big Bang Nucleosynthesis on MeV-scale particles ϕ which decay into photons and/or electron-positron pairs. We use the latest determinations of primordial abundances and extend the analysis in [1] by including all spin-statistical factors as well as inverse decays, significantly strengthening the resulting bounds in particular for small masses. For a very suppressed initial abundance of ϕ, these effects become ever more important and we find that even a pure `freeze-in' abundance can be significantly constrained. In parallel to this article, we release the public code ACROPOLIS which numerically solves the reaction network necessary to evaluate the effect of photodisintegration on the final light element abundances. As an interesting application, we re-evaluate a possible solution of the lithium problem due to the photodisintegration of beryllium and find that e.g. an ALP produced via freeze-in can lead to a viable solution.

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“…The excess over 3 encodes the effective heating of neutrinos during e + e − annihilation. The remaining theoretical uncertainty comes from approximations made in the treatment of finite temperature and/or higher-loop QED effects [330], non-perturbative effects, etc. The deviations of N eff from 3 reflects the fact that the active neutrinos are not described by an exact Fermi-Dirac distribution with T std ν = (4/11) 1/3 T .…”

Section: Number Of Neutrinosmentioning

confidence: 99%

Sterile Neutrinos

Dasgupta,

Kopp

2021

Preprint

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Neutrinos, being the only fermions in the Standard Model of Particle Physics that do not possess electromagnetic or color charges, have the unique opportunity to communicate with fermions outside the Standard Model through mass mixing. Such Standard Modelsinglet fermions are generally referred to as "sterile neutrinos". In this review article, we discuss the theoretical and experimental motivation for sterile neutrinos, as well as their phenomenological consequences. With the benefit of hindsight in 2020, we point out potentially viable and interesting ideas. We focus in particular on sterile neutrinos that are light enough to participate in neutrino oscillations, but we also comment on the benefits of introducing heavier sterile states. We discuss the phenomenology of eVscale sterile neutrinos in terrestrial experiments and in cosmology, we survey the global data, and we highlight various intriguing anomalies. We also expose the severe tension that exists between different data sets and prevents a consistent interpretation of the global data in at least the simplest sterile neutrino models. We discuss non-minimal scenarios that may alleviate some of this tension. We briefly review the status of keV-scale sterile neutrinos as dark matter and the possibility of explaining the matter-antimatter asymmetry of the Universe through leptogenesis driven by yet heavier sterile neutrinos.

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Addendum: Towards a precision calculation of the effective number of neutrinos N _eff in the Standard Model: the QED equation of state

Cited by 15 publications

References 0 publications

Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches

Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches

Updated BBN constraints on electromagnetic decays of MeV-scale particles

Sterile Neutrinos

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Addendum: Towards a precision calculation of the effective number of neutrinos N eff in the Standard Model: the QED equation of state

Cited by 15 publications

References 0 publications

Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches

Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches

Updated BBN constraints on electromagnetic decays of MeV-scale particles

Sterile Neutrinos

Contact Info

Product

Resources

About

Addendum: Towards a precision calculation of the effective number of neutrinos N _eff in the Standard Model: the QED equation of state