Cornering (quasi) degenerate neutrinos with cosmology

In light of the improved sensitivities of cosmological observations, we examine the status of quasi-degenerate neutrino mass scenarios. Within the simplest extension of the standard cosmological model with massive neutrinos, we find that quasi-degenerate neutrinos are severely constrained by present cosmological data and neutrino oscillation experiments. We find that Planck 2018 observations of cosmic microwave background (CMB) anisotropies disfavour quasi-degenerate neutrino masses at 2.4 Gaussian σ’s, while adding baryon acoustic oscillations (BAO) data brings the rejection to 5.9σ’s. The highest statistical significance with which one would be able to rule out quasi-degeneracy would arise if the sum of neutrino masses is ∑mv = 60 meV (the minimum allowed by neutrino oscillation experiments); indeed a sensitivity of 15 meV, as expected from a combination of future cosmological probes, would further improve the rejection level up to 17σ. We discuss the robustness of these projections with respect to assumptions on the underlying cosmological model, and also compare them with bounds from β decay endpoint and neutrinoless double beta decay studies.

Update constraints on neutrino mass and mass hierarchy in light of dark energy models

Combining cosmic microwave (CMB) background data from Planck satellite data, Baryon Acoustic Oscillations (BAO) measurements and Type Ia supernovae (SNe Ia) data, we obtain the bounds on total neutrino masses [Formula: see text] with the approximation of degenerate neutrino masses and for three dark energy models: the cosmological constant ([Formula: see text]CDM) model, a phenomenological emergent dark energy (PEDE) model and a model-independent quintessential parametrization (HBK). The bounds on the sum of neutrino masses [Formula: see text] depend on the dark energy (DE) models. In the HBK model, we confirm the conclusion from some previous work that the quintessence prior of DE tends to tighten the cosmological constraint on [Formula: see text]. On the other hand, the PEDE model leads to larger [Formula: see text] and a nonzero lower bound. Besides, we also explore the correlation between three different neutrino hierarchies and DE models.

Leptogenesis in quasi-degenerate neutrino mass models with non-zero θ13

In the context of neutrino oscillation experiments, six different quasi-degenerate neutrino (QDN) mass models, which we parameterized recently, are found equally relevant. The present attempt tries to explore the possibilities for the discrimination of the six QDN models in the light of baryogenesis via leptogenesis. In this work we investigate all six models to predict observable baryon asymmetry. If leptogenesis is unflavoured or single flavoured, a significant difference is found. Then, only QD-NH-IA and QD-IH-IA are dominant. To get specific results, the choice of Dirac neutrino mass matrix as down-quark type is found most favourable.

Dark matter in the local group of galaxies

We describe the neutrino flavor ([Formula: see text], [Formula: see text], [Formula: see text]) masses as [Formula: see text] [Formula: see text] with [Formula: see text] and probably [Formula: see text]. The quantity [Formula: see text] is the degenerate neutrino mass. Because neutrino flavor is not a quantum number, this degenerate mass appears in the neutrino equation-of-state [P. D. Morley and D. J. Buettner, Int. J. Mod. Phys. D (2014), doi:10.1142/s0218271815500042.]. We apply a Monte Carlo computational physics technique to the Local Group (LG) of galaxies to determine an approximate location for a Dark Matter embedding Condensed Neutrino Object (CNO) [P. D. Morley and D. J. Buettner, Int. J. Mod. Phys. D (2016), doi:10.1142/s0218271816500899.]. The calculation is based on the rotational properties of the only spiral galaxies within the LG: M31, M33 and the Milky Way. CNOs could be the Dark Matter everyone is looking for and we estimate the CNO embedding the LG to have a mass 5.17[Formula: see text] M[Formula: see text] and a radius 1.316 Mpc, with the estimated value of [Formula: see text] eV[Formula: see text]/c2. The up-coming KATRIN experiment [https://www.katrin.kit.edu.] will either be the definitive result or eliminate condensed neutrinos as a Dark Matter candidate.

SHM of galaxies embedded within condensed neutrino matter

We re-examine the question of condensed neutrino objects (degenerate neutrino matter) based on new calculations. The potential show-stopper issue of free-streaming light neutrinos inhibiting galaxy formation is addressed. We compute the period associated with simple harmonic motion (SHM) of galaxies embedded within condensed neutrino objects. For observational consequences, we examine the rotational velocities of embedded galaxies using Hickson 88A (N6978) as the prototype. Finally, we point out that degenerate neutrino objects repel each other in overlap and we compute directly the repulsive force between two interesting and relevant configurations. An outstanding issue is whether the accompanying tidal forces generated by condensed neutrino matter on embedded galaxies give rise to galactic bulges and halos.

EVOLUTION OF DISTRIBUTION FUNCTION FOR COSMOLOGICAL NEUTRINO

Recent experimental evidences show that the universe is accelerating. There are many modified cosmological models to explain this accelerating phase including ΛCDM, quintessence model, Brans-Dicke, f(R) gravity, and others. In this talk we want to check the possibility of explaining the current accelerating phase using standard cosmological model with degenerate neutrino. We will study the evolution of distribution function of degenerate neutrinos with standard Friedmann-Lemaître-Roberston-Walker(FLRW) background.