Influence of a keV sterile neutrino on neutrino-less double beta decay -- how things changed in the recent years

Earlier studies of the influence of Dark Matter keV sterile neutrinos on neutrino-less double beta decay concluded that there is no significant modification of the decay rate. These studies have focused only on a mass of the keV sterile neutrino above 2 and 4 keV, respectively, as motivated by certain production mechanisms. On the other hand, alternative production mechanisms have been proposed, which relax the lower limit for the mass, and new experimental data are available, too. For this reason, an updated study is timely and worthwhile. We focus on the most recent data, i.e., the newest Chandra and XMM-Newton observational bounds on the X-ray line originating from radiative keV sterile neutrino decay, as well as the new measurement of the previously unknown leptonic mixing angle $\theta_{13}$. While the previous works might have been a little short-sighted, the new observational bounds do indeed render any influences of keV sterile neutrinos on neutrino-less double beta decay small. This conclusion even holds in case not all the Dark Matter is made up of keV sterile neutrinos.Comment: 24 pages, 5 figures, text reorganized, numerical analysis improved, figures added, conclusions unchange

Una asociación desigual: los proveedores de servicios de reasentamiento en Australia

La relación entre los proveedores de servicios de reasentamiento de refugiados del gobierno y los contratados por el gobierno australiano debe basarse más en autonomía y confianza

New Production Mechanism for keV Sterile Neutrino Dark Matter by Decays of Frozen-In Scalars

We propose a new production mechanism for keV sterile neutrino Dark Matter. In our setting, we assume the existence of a scalar singlet particle which never entered thermal equilibrium in the early Universe, since it only couples to the Standard Model fields by a really small Higgs portal interaction. For suitable values of this coupling, the scalar can undergo the so-called freeze-in process, and in this way be efficiently produced in the early Universe. These scalars can then decay into keV sterile neutrinos and produce the correct Dark Matter abundance. While similar settings in which the scalar does enter thermal equilibrium and then freezes out have been studied previously, the mechanism proposed here is new and represents a versatile extension of the known case. We perform a detailed numerical calculation of the DM production using a set of coupled Boltzmann equations, and we illustrate the successful regions in the parameter space. Our production mechanism notably can even work in models where active-sterile mixing is completely absent

Statistical tests of sterile neutrinos using cosmology and short-baseline data

In this paper we revisit the question of the information which cosmology provides on the scenarios with sterile neutrinos invoked to describe the SBL anomalies using Bayesian statistical tests. We perform an analysis of the cosmological data in $\Lambda$CDM$+r+\nu_s$ cosmologies for different cosmological data combinations, and obtain the marginalized cosmological likelihood in terms of the two relevant parameters, the sterile neutrino mass $m_s$ and its contribution to the energy density of the early Universe $N_{\rm eff}$. We then present an analysis to quantify at which level a model with one sterile neutrino is (dis)favoured with respect to a model with only three active neutrinos, using results from both short-baseline experiments and cosmology. We study the dependence of the results on the cosmological data considered, in particular on the inclusion of the recent BICEP2 results and the SZ cluster data from the Planck mission. We find that only when the cluster data is included the model with one extra sterile neutrino can become more favoured that the model with only the three active ones provided the sterile neutrino contribution to radiation density is suppressed with respect to the fully thermalized scenario. We have also quantified the level of (in)compatibility between the sterile neutrino masses implied by the cosmological and SBL results.Comment: 23 pages, 4 figure

A consistent model for leptogenesis, dark matter and the IceCube signal

We discuss a left-right symmetric extension of the Standard Model in which the three additional right-handed neutrinos play a central role in explaining the baryon asymmetry of the Universe, the dark matter abundance and the ultra energetic signal detected by the IceCube experiment. The energy spectrum and neutrino flux measured by IceCube are ascribed to the decays of the lightest right-handed neutrino $N_1$, thus fixing its mass and lifetime, while the production of $N_1$ in the primordial thermal bath occurs via a freeze-in mechanism driven by the additional $SU(2)_R$ interactions. The constraints imposed by IceCube and the dark matter abundance allow nonetheless the heavier right-handed neutrinos to realize a standard type-I seesaw leptogenesis, with the $B-L$ asymmetry dominantly produced by the next-to-lightest neutrino $N_2$. Further consequences and predictions of the model are that: the $N_1$ production implies a specific power-law relation between the reheating temperature of the Universe and the vacuum expectation value of the $SU(2)_R$ triplet; leptogenesis imposes a lower bound on the reheating temperature of the Universe at 7\times10^9\,\mbox{GeV}. Additionally, the model requires a vanishing absolute neutrino mass scale $m_1\simeq0$.Comment: 19 pages, 4 figures. Constraints from cosmic-ray antiprotons and gamma rays added, with hadrophobic assignment of the matter multiplets to satisfy bounds. References added. Matches version published in JHE

Enhancing Dark Matter Annihilation into Neutrinos

We perform a detailed and quasi model-independent analysis of direct annihilation of Dark Matter into neutrinos. Considering different cases for scalar and fermionic Dark Matter, we identify several settings in which this annihilation is enhanced, contrary to some statements in the literature. They key point is that several restrictions of, e.g., a supersymmetric framework do not hold in general. The mass generation mechanism of the neutrinos plays an important role, too. We illustrate our considerations by two examples that are not (as usually) suppressed by the smallness of the neutrino mass, for which we also present a numerical analysis. Our results can be easily used as guidelines for model building.Comment: 33 pages, 2 figure

Leptophilic Dark Matter in Direct Detection Experiments and in the Sun

Dark matter interacting predominantly with leptons instead of nuclear matter has received a lot of interest recently. In this talk, we investigate the signals expected from such 'leptophilic Dark Matter' in direct detection experiments and in experiments looking for Dark Matter annihilation into neutrinos in the Sun. In a model-independent framework, we calculate the expected interaction rates for different scattering processes, including elastic and inelastic scattering off atomic electron shells, as well as loop-induced scattering off atomic nuclei. In those cases where the last effect dominates, leptophilic Dark Matter cannot be distinguished from conventional WIMPs. On the other hand, if inelastic scattering off the electron shell dominates, the expected event spectrum in direct detection experiments is different and would provide a distinct signal. However, we find that the signals in DAMA and/or CoGeNT cannot be explained by invoking leptophilic DM because the predicted and observed energy spectra do not match, and because of neutrino bounds from the Sun.Comment: 7 pages, 3 figures, prepared for the Proceedings of the 8th International Workshop on Identification of Dark Matter (IDM 2010), July 26-30, 2010, University of Montpellier II, Montpellier, Franc