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Abstract |
The electron neutrino degeneracy parameter, xi(ve) = mu(ve)/T, is tightly constrained by Big Bang Nucleosynthesis (BBN), while the degeneracy parameters of the other neutrino species, xi(vx), remain weakly constrained by cosmological observations alone. In this manuscript we shall compute up-to-date bounds on xi(ve) and xi(vx) assuming that either they are constant free-parameters along the cosmic history or that they are redshift dependent quantities. In the latter case we employ a model-independent reconstruction approach based on the Piecewise Cubic Hermite Interpolating Polynomial (PCHIP) formalism with four nodes, located at z similar or equal to 10, 100, 1000 and 10(8). We shall also consider two scenarios for neutrinos, specifically three degenerate neutrinos (xi(ve) = xi(vx)) and the case in which we actually differentiate between xi(ve) and xi(vx). We perform a cosmological analysis combining CMB data from Planck, SPT, and ACT with BAO measurements from DESI, showing the impact of including BBN observables from either EMPRESS results, which allow for a non-zero chemical potential, or from LBT observations, compatible with the standard xi(v) = 0 prediction. We explicitly show that the BBN data, via the change in neutron-to-proton inter-conversion rates, mostly constrain xi(ve), a parameter for which we observe a preferred non-zero positive value at 95% C.L. in the non-degenerate neutrino case at the BBN period. Since the Hubble constant is correlated with xi(v), through N-eff, a larger value of H-0 is allowed within these models, making them really interesting scenarios where to test non-standard physics models. |
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Address |
[Ghedini, Pietro] UV, Inst Fis Corpuscular IFIC, CSIC, Valencia, Spain; [Ghedini, Pietro] UV, Dept Fis Teor, Valencia, Spain; [Impavido, Riccardo] Univ Ferrara, Dipartimento Fis & Sci Terra, Via Giuseppe Saragat 1, I-44122 Ferrara, Italy; [Impavido, Riccardo] Sez Ferrara, INFN, Via Giuseppe Saragat 1, I-44122 Ferrara, Italy; [Gariazzo, Stefano] Univ Valencia, Inst Fis Corpuscular IFIC, CSIC, Valencia, Spain; [Gariazzo, Stefano; Mena, Olga; Wang, Deng] Univ Turin, Phys Dept, Via P Giuria 1, I-10125 Turin, Italy; [Gariazzo, Stefano; Mena, Olga; Wang, Deng] INFN, Sez Torino, Via P Giuria 1, I-10125 Turin, Italy, Email: pietro.ghedini@ific.uv.es; |
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