A precision calculation of the effective number of cosmological neutrinos

By G. Mangano, G. Miele, S. Pastor, Marco Peloso. 2001

244 citations recorded by the source corpus.

Abstract The neutrino energy density of the Universe can be conveniently parametrized in terms of the so-called effective number of neutrinos, Nνeff. This parameter enters in several cosmological observables. In particular it is an important input in those numerical codes, like CMBFAST, which are used to study the Cosmic Microwave Background anisotropy spectrum. By studying the neutrino decoupling with Boltzmann equations, one can show that this quantity differs from the number of massless neutrino species for an additional contribution due to a partial heating of neutrinos during the e± annihilations, leading to non-thermal features in their final distributions. In this Letter we review the different results obtained in the literature and perform a new analysis which takes into account, in a fully consistent way, the QED corrections at finite temperature to the photon and e± plasma equation of state. The value found for three massless active neutrinos is Nνeff=3.0395, in perfect agreement with the recommended value used in CMBFAST, Nνeff=3.04. We also discuss the case of additional relativistic relics and massive active neutrinos.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/0045bad0bc7af2e45b0a346f1f3fc33fd4f85880

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Citations in the corpus

FIVE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2008, unknown): “With other subtle corrections included, the current standard value is N standardeff = 3.04 (Dicus et al. 1982; Gnedin & Gnedin 1998; Dolgov et al. 1999; Mangano et al. 2002).”
The Cardassian expansion revisited: constraints from updated Hubble parameter measurements and type Ia supernova data (2017, background): “We compute Ωr0 = 2.469 × 10−5h−2(1 + 0.2271Neff ) (Komatsu et al. 2011), where Neff = 3.04 is the standard number of relativistic species (Mangano et al. 2002).”
Flavor structures of charged fermions and massive neutrinos (2019, background): “046 predicted by the standard cosmological model [333, 334].”
Phases of new physics in the CMB (2015, background): “046 [20]), but also characterizes any free-streaming radiation density beyond the SM expectation (including additional energy in neutrinos).”
Neutrino decoupling including flavour oscillations and primordial nucleosynthesis (2020, background): “However, in the context of neutrino decoupling in the early universe, one seeks a generalization of the Boltzmann equation for neutrino distribution functions [3–7], which describes the evolution of densities under two-body collisions.”
Relic neutrino decoupling with flavour oscillations revisited (2016, methodology): “In previous analyses of neutrino decoupling, this system was solved either using a discretization in a grid for the neutrino momenta yi as in [6–9, 12, 14] or expanding the non-thermal distortions of the neutrino distribution functions in moments as in [10, 11, 13].”
Neutrino decoupling beyond the Standard Model: CMB constraints on the Dark Matter mass with a fast and precise Neff evaluation (2018, methodology): “The agreement between the observations of the Cosmic Microwave Background (CMB) [1, 2], and the primordial element abundances [3, 4] with the SM prediction [5–15] of three relativistic neutrino species represents a success of the Standard Model, and constitues a non-trivial test for some of its exte”
Non-Abelian dark matter and dark radiation (2015, unknown): “46 at 95% confidence to be compared with the SM prediction [43] N eff = 3.”
Alleviating the H0 and σ8 anomalies with a decaying dark matter model (2019, background): “sity ˆ rad of relativistic species in terms of the photon energy density ˆ is ˆ rad = " 1 + 7 8 N e 4 11 4=3 # ˆ : (2.8) This includes standard model (SM) neutrinos (for which N ;e = 3:046) [42,43], and characterizes any free-streaming radiation beyond the SM expectation. Then, any departure ”