Search results for "sterile"
showing 10 items of 164 documents
Four species neutrino oscillations at nu-Factory: sensitivity and CP-violation
1999
The prospects of measuring the leptonic angles and CP-odd phases at a {\em neutrino factory} are discussed in the scenario of three active plus one sterile neutrino. We consider the $\nu_\mu \raw \nu_e$ LSND signal. Its associated large mass difference leads to observable neutrino oscillations at short ($\sim 1$ km) baseline experiments. Sensitivities to the leptonic angles down to $10^{-3}$ can be easily achieved with a 1 Ton detector. Longer baseline experiments ($\sim 100$ km) with a 1 Kton detector can provide very clean tests of CP-violation especially through tau lepton detection.
Reconciling dark matter and solar neutrinos
1993
Abstract We present a simple model for neutrino dark matter in which neutrino masses arise radiatively and the solar neutrino data are explained via the MSW effect. The dark matter scale arises at the one-loop level with the MSW scale arises only in two loops. The model is compatible with all observational facts and allows observable ν e ν τ or ν μ ν τ oscillation rates in the laboratory if the limits from primordial big bang nucleosynthesis (BBN) are taken conservatively. In addition, it can be probed by searching for muon number violating processes such as μ → e + γ , and μ →3 e . These rates can well lie within the sensitivities of present experiments. Finally, if we ignore BBN limits we…
Reconstructing Neutrino Properties from Collider Experiments in a Higgs Triplet Neutrino Mass Model
2003
We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a pair of Higgs triplet superfields. The neutral components of the Higgs triplets develop small vacuum expectation values (VEVs) quadratic in the bilinear R-parity breaking parameters. In this scheme the atmospheric neutrino mass scale arises from bilinear R-parity breaking while for reasonable values of parameters the solar neutrino mass scale is generated from the small Higgs triplet VEVs. We calculate neutrino masses and mixing angles in this model and show how the model can be tested at future colliders. The branching ratios of the doubly charged triplet decays are related to the solar neutri…
Status of the MSW solutions of the solar neutrino problem
2000
We present an updated global analysis of two-flavor MSW solutions to the solar neutrino problem in terms of conversions of nu_e into active or sterile neutrinos. We perform a fit to the full data set corresponding to the 825-day Super-Kamiokande data sample as well as to Chlorine, GALLEX and SAGE experiments. We use all measured total event rates as well as Super-Kamiokande data on the zenith angle dependence, energy spectrum and seasonal variation of the events. For conversions into active neutrinos we find that, although the data on the total event rates favours the Small Mixing Angle (SMA) solution, once the full data set is included both SMA and Large Mixing Angle (LMA) solutions give a…
Oscillations of Dirac and Majorana neutrinos in matter and a magnetic field
2008
We study the evolution of massive mixed Dirac and Majorana neutrinos in matter under the influence of a transversal magnetic field. The analysis is based on relativistic quantum mechanics. We solve exactly the evolution equation for relativistic neutrinos, find the neutrino wave functions, and calculate the transition probability for spin-flavor oscillations. We analyze the dependence of the transition probability on the external fields and compare the cases of Dirac and Majorana neutrinos. The evolution of Majorana particles in vacuum is also studied and correction terms to the standard oscillation formula are derived and discussed. As a possible application of our results we discuss the s…
Sterile neutrino signals from supernovae
2007
We investigate the effects of a mixing of active and sterile neutrinos on the ratios of supernova electron neutrino flux ($F_e$) and antineutrino flux ($F_{\bar e}$) to the total flux of the other neutrino and antineutrino flavours ($F_a$). We assume that the heaviest (in the normal hierarchy) Standard Model neutrino $\nu_3$ mixes with a sterile neutrino resulting in a pair of mass eigenstates with a small mass gap. Using the density matrix formalism we solve numerically the the evolution of neutrino states in the envelope of a supernova and determine the flux ratios $F_e/F_a$ and $F_{\bar{e}}/F_a$ as a function of the active-sterile mixing angle and for the experimentally allowed range of …
Minimal models with light sterile neutrinos
2011
We study the constraints imposed by neutrino oscillation experiments on the minimal extensions of the Standard Model (SM) with $n_R$ gauge singlet fermions ("right-handed neutrinos"), that can account for neutrino masses. We consider the most general coupling to SM fields of the new fields, in particular those that break lepton number and we do not assume any a priori hierarchy in the mass parameters. We proceed to analyze these models starting from the lowest level of complexity, defined by the number of extra fermionic degrees of freedom. The simplest choice that has enough free parameters in principle (i.e. two mass differences and two angles) to explain the confirmed solar and atmospher…
Low-scale seesaw models versusNeff
2014
We consider the contribution of the extra sterile states in generic low-scale seesaw models to extra radiation, parametrized by ${N}_{\text{eff}}$. We find that the value of ${N}_{\text{eff}}$ is roughly independent of the seesaw scale within a wide range. We explore the full parameter space in the case of two extra sterile states and find that these models are strongly constrained by cosmological data for any value of the seesaw scale below $\mathcal{O}(100\text{ }\text{ }\mathrm{MeV})$.
The Minimal 3 + 2 Neutrino Model vs. Higgs Decays
2016
Abstract The minimal 3+2 neutrino model is a Type-I seesaw model with two Weyl fermions, singlets under the Standard Model. Apart from light neutrino masses and mixings, this model can be fully described by four additional parameters. In this work, we study the minimal 3+2 neutrino model in scenarios where the singlets have masses at the GeV scale. This can lead to Higgs decays into heavy neutrinos, which could be observable as displaced vertices at the LHC.
Neutrino conversions in hot plasma
1995
We discuss the excitation of sterile neutrinos in the early universe using general quantum kinetic equations, which also incorporate a possible primordial magnetic field $B$. We find a new contribution to the excitation propability, which has its origin in the shrinkage of the spin vector. In the absence of $B$ nucleosynthesis implies the constraint $\mid \Delta m^2\mid\sin^22\theta_0\lsim 1.6\times 10^{-6}~{\rm eV}^2$ which is more restrictive than previous estimates. We also present examples of possible stringent limits for $B\ne 0$.