Dark matter origins of neutrino masses

We propose a simple scenario that directly connects the dark matter (DM) and neutrino mass scales. Based on an interaction between the DM particle $chi$ and the neutrino $ u$ of the form $chichi u u/Lambda^2$, the DM annihilation cross section into the neutrino is determined and a neutrino mass is radiatively induced. Using the observed neutrino mass scale and the DM relic density, the DM mass and the effective scale $Lambda$ are found to be of the order MeV and GeV, respectively. We construct an ultraviolet-complete toy model based on the inverse seesaw mechanism which realizes this potential connection between DM and neutrino physics.

On the Minimum Dark Matter Mass Testable by Neutrinos from the Sun

We discuss a limitation on extracting bounds on the scattering cross section of dark matter with nucleons, using neutrinos from the Sun. If the dark matter particle is sufficiently light (less than about 4 GeV), the effect of evaporation is not negligible and the capture process goes in equilibrium with the evaporation. In this regime, the flux of solar neutrinos of dark matter origin becomes independent of the scattering cross section and therefore no constraint can be placed on it. We find the minimum values of dark matter masses for which the scattering cross section on nucleons can be probed using neutrinos from the Sun. We also provide simple and accurate fitting functions for all the relevant processes of GeV-scale dark matter in the Sun.

Dark Matter From Weak Polyplets

The addition of new multiplets of fermions charged under the Standard Model gauge group is investigated, with the aim of identifying a possible dark matter candidate. These fermions are charged under $SU(2)times U(1)$, and their quantum numbers are determined by requiring all new particles to obtain masses via Yukawa couplings and all triangle anomalies to cancel as in the Standard Model; more than one multiplet is required and we refer to such a set of these multiplets as a polyplet. For sufficiently large multiplets, the stability of the dark matter candidate is ensured by an accidental symmetry; for clarity, however, we introduce a model with a particularly simple polyplet structure and stabilize the dark matter by imposing a new discrete symmetry. We then explore the features of this model; constraints from colliders, electroweak precision measurements, the dark matter relic density, and direct detection experiments are considered. We find that the model can accommodate a viable dark matter candidate for large Higgs boson masses; for $m_Hsim 125$ GeV, a subdominant contribution to the dark matter relic density can be achieved.

Pseudo-Dirac Neutrinos in the New Standard Model

The addition of gauge singlet fermions to the Standard Model Lagrangian renders the neutrinos massive and allows one to explain all that is experimentally known about neutrino masses and lepton mixing by varying the values of the Majorana mass parameters M for the gauge singlets and the neutrino Yukawa couplings. Here we explore the region of parameter space where M values are much smaller than the neutrino Dirac masses. In this region, neutrinos are pseudo-Dirac fermions. We find that current solar data constrain M values to be less than at least 1E-9 eV, and discuss the sensitivity of future experiments to tiny gauge singlet fermion masses. We also discuss a useful basis for analyzing pseudo-Dirac neutrino mixing effects. In particular, we identify a simple relationship between elements of M and the induced enlarged mixing matrix and new mass-squared differences. These allow one to directly relate bounds on the new mass-squared differences to bounds on the singlet fermion Majorana masses.