Search

We consider invisible neutrino decay ν H → ν l + ϕ in the ultra-relativistic limit and compute the neutrino anisotropy loss rate relevant for the cosmic microwave background (CMB) anisotropies. Improving on our previous work which assumed massless ν l and ϕ , we reinstate in this work the daughter neutrino mass m ν l in a manner consistent with the experimentally determined neutrino mass splittings. We find that a nonzero m ν l introduces a new phase space factor in the loss rate Γ T proportional to (Δ m ν 2 / m ν H 2) 2 in the limit of a small squared mass gap between the parent and daughter neutrinos, i.e., Γ T ∼ (Δ m ν 2 / m ν H 2) 2 (m ν H / E ν) 5 (1 / τ 0) , where τ 0 is the ν H rest-frame lifetime. Using a general form of this result, we update the limit on τ 0 using the Planck 2018 CMB data. We find that for a parent neutrino of mass m ν H ≲ 0.1 eV, the new phase space factor weakens the constraint on its lifetime by up to a factor of 50 if Δ m ν 2 corresponds to the atmospheric mass gap and up to 10 5 if the solar mass gap, in comparison with naïve estimates that assume m ν l = 0 . The revised constraints are (i) τ 0 ≳ (6 → 10) × 10 5 s and τ 0 ≳ (400 → 500) s if only one neutrino decays to a daughter neutrino separated by, respectively, the atmospheric and the solar mass gap, and (ii) τ 0 ≳ (2 → 6) × 10 7 s in the case of two decay channels with one near-common atmospheric mass gap. In contrast to previous, naïve limits which scale as m ν H 5 , these mass spectrum-consistent τ 0 constraints are remarkably independent of the parent mass and open up a swath of parameter space within the projected reach of IceCube and other neutrino telescopes in the next two decades. [ABSTRACT FROM AUTHOR]

The density of relic neutrinos is expected to be enhanced due to clustering in our local neighbourhood at Earth. We introduce a novel analytical technique to calculate the neutrino overdensity, based on kinetic field theory. Kinetic field theory is a particle-based theory for cosmic structure formation and in this work we apply it for the first time to massive neutrinos. The gravitational interaction is expanded in a perturbation series and we take into account the first-order contribution to the local density of relic neutrinos. For neutrino masses that are consistent with cosmological neutrino mass bounds, our results are in excellent agreement with state-of-the-art calculations. [ABSTRACT FROM AUTHOR]

We investigate how a lepton asymmetry impacts the cosmic trajectory in the QCD phase diagram. We study the evolution of chemical potentials during the QCD epoch of the early Universe using susceptibilities from lattice QCD to interpolate between an ideal quark gas and an ideal hadron resonance gas. The lepton asymmetry affects the evolution of all chemical potentials. The standard cosmic trajectory is obtained assuming tiny lepton and baryon asymmetries. For larger lepton asymmetry, the charge chemical potential exceeds the baryon chemical potential before pion annihilation. [ABSTRACT FROM AUTHOR]