Search

We perform a global analysis of neutrino data in the framework of three massive neutrinos with non-standard neutrino interactions which affect their evolution in the matter background. We focus on the effect of NSI in the present observables sensitive to leptonic CP violation and to the mass ordering. We consider complex neutral current neutrino interactions with quarks whose lepton-flavor structure is independent of the quark type. We quantify the status of the "hints" for CP violation, the mass-ordering and non-maximality of θ23 in these scenarios. We also present a parametrization-invariant formalism for leptonic CP violation in presence of a generalized matter potential induced by NSI., This work is supported by USA-NSF grant PHY-1620628, by EU Networks FP10 ITN ELUSIVES (H2020-MSCA-ITN-2015-674896) and INVISIBLES-PLUS (H2020-MSCA-RISE-2015-690575), by MINECO grant FPA2016-76005-C2-1-P and MINECO/FEDER-UE grants FPA2015-65929-P and FPA2016-78645-P, by Maria de Maetzu program grant MDM-2014-0367 of ICCUB, and by the "Severo Ochoa" program grant SEV-2016-0597 of IFT. I.E. acknowledges support from the FPU program fellowship FPU15/03697.

We quantify the effect of gauge bosons from a weakly coupled lepton flavor dependent U(1)' interaction on the matter background in the evolution of solar, atmospheric, reactor and long-baseline accelerator neutrinos in the global analysis of oscillation data. The analysis is performed for interaction lengths ranging from the Sun-Earth distance to effective contact neutrino interactions. We survey ~10000 set of models characterized by the six relevant fermion U(1)' charges and find that in all cases, constraints on the coupling and mass of the Z' can be derived. We also find that about 5% of the U(1)' model charges lead to a viable LMA-D solution but this is only possible in the contact interaction limit. We explicitly quantify the constraints for a variety of models including U(1) B - 3Le, U(1) B - 3Lµ, U(1) B - 3Lτ, U(1) B - 3/2 (Lµ+Lτ) , U(1) Le - Lµ , U(1) Le - Lτ , U(1) Le - 1/2 (Lµ+Lτ). We compare the constraints imposed by our oscillation analysis with the strongest bounds from fifth force searches, violation of equivalence principle as well as bounds from scattering experiments and white dwarf cooling. Our results show that generically, the oscillation analysis improves over the existing bounds from gravity tests for Z' lighter than ∼ 1e-8 → 1e-11 eV depending on the specific couplings. In the contact interaction limit, we find that for most models listed above there are values of g' and MZ' for which the oscillation analysis provides constraints beyond those imposed by laboratory experiments. Finally we illustrate the range of Z' and couplings leading to a viable LMA-D solution for two sets of models., The authors acknowledge use of the HPC facilities at the IFT (Hydra cluster). This work was supported by the Spanish grants FPA2016-76005-C2-1-P, FPA2016-78645-P, PID2019-105614GB-C21 and PID2019-110058GB-C21, by EU Network FP10 ITN HIDDEN (H2020-MSCA-ITN-2019-860881), by USA-NSF grant PHY-1915093, by AGAUR (Generalitat de Catalunya) grant 2017-SGR-929. The authors acknowledge the support of the Spanish Agencia Estatal de Investigación through the grant “IFT Centro de Excelencia Severo Ochoa SEV-2016-0597”. PC acknowledges funding from the Spanish MICINN through the “Ramon y Cajal” program under grant RYC2018-024240-I.

In this addendum we re-assess the constraints on Non-Standard Interactions (NSI) from the combined analysis of data from oscillation experiments and from COHERENT after including the new data released since the publication of ref. [1]., This work was supported by the spanish grants FPA2016-76005-C2-1-P, FPA2016-78645-P, PID2019-105614GB-C21 and PID2019-110058GB-C21, by USA-NSF grant PHY-1915093, – 5 – JHEP12(2020)071 by AGAUR (Generalitat de Catalunya) grant 2017-SGR-929, by EU ITN project H2020- MSCA-ITN-2019/870881-HIDDeN, and by the Spanish Agencia Estatal de Investigación through the grant “IFT Centro de Excelencia Severo Ochoa SEV-2016-0597”. IE acknowledges support from the FPU program fellowship FPU15/0369. The authors acknowledge use of the HPC facilities at the IFT (Hydra cluster)

We perform a global fit to neutrino oscillation and coherent neutrino-nucleus scattering data, using both timing and energy information from the COHERENT experiment. The results are used to set model-independent bounds on four-fermion effective operators inducing non-standard neutral-current neutrino interactions. We quantify the allowed ranges for their Wilson coefficients, as well as the status of the LMA-D solution, for a wide class of new physics models with arbitrary ratios between the strength of the operators involving up and down quarks. Our results are presented for the COHERENT experiment alone, as well as in combination with the global data from oscillation experiments. We also quantify the dependence of our results for COHERENT with respect to the choice of quenching factor, nuclear form factor, and the treatment of the backgrounds., This work was supported by the MINECO grant FPA2016-76005-C2-1-P, by the MINECO FEDER/UE grants FPA2015-65929-P, FPA2016-78645-P and FPA2017-85985-P, by PROMETEO/2019/083, by USA-NSF grants PHY-1620628, by EU Networks FP10 ITN ELUSIVES (H2020-MSCA-ITN-2015-674896) and INVISIBLES-PLUS (H2020-MSCA-RISE-2015-690575), by the “Severo Ochoa” program grant SEV-2016-0597 of IFT and by AGAUR (Generalitat de Catalunya) grant 2017-SGR-929. IE acknowledges support from the FPU program fellowship FPU15/0369.

We present the results of a global analysis of the neutrino oscillation data available as of fall 2018 in the framework of three massive mixed neutrinos with the goal at determining the ranges of allowed values for the six relevant parameters. We describe the complementarity and quantify the tensions among the results of the different data samples contributing to the determination of each parameter. We also show how those vary when combining our global likelihood with the χ map provided by Super-Kamiokande for their atmospheric neutrino data analysis in the same framework. The best fit of the analysis is for the normal mass ordering with inverted ordering being disfavoured with a Δχ = 4.7 (9.3) without (with) SK-atm. We find a preference for the second octant of θ , disfavouring the first octant with Δχ = 4.4 (6.0) without (with) SK-atm. The best fit for the complex phase is δ = 215° with CP conservation being allowed at Δχ = 1.5 (1.8). As a byproduct we quantify the correlated ranges for the laboratory observables sensitive to the absolute neutrino mass scale in beta decay, mνe , and neutrino-less double beta decay, m , and the total mass of the neutrinos, Σ, which is most relevant in Cosmology., This work is supported by USA-NSF grant PHY-1620628, by EU Networks FP10 ITN ELUSIVES (H2020-MSCA-ITN-2015-674896) and INVISIBLES-PLUS (H2020-MSCA-RISE2015-690575), by MINECO grant FPA2016-76005-C2-1-P and MINECO/FEDER-UE grants FPA2015-65929-P and FPA2016-78645-P, by Maria de Maetzu program grant MDM2014-0367 of ICCUB, and by the “Severo Ochoa” program grant SEV-2016-0597 of IFT. I.E. acknowledges support from the FPU program fellowship FPU15/03697.

We discuss the possibility to explain the anomalies in short-baseline neutrino oscillation experiments in terms of sterile neutrinos. We work in a 3+1 framework and pay special attention to recent new data from reactor experiments, IceCube and MINOS+. We find that results from the DANSS and NEOS reactor experiments support the sterile neutrino explanation of the reactor anomaly, based on an analysis that relies solely on the relative comparison of measured reactor spectra. Global data from the $\nu_e$ disappearance channel favour sterile neutrino oscillations at the $3\sigma$ level with $\Delta m^2_{41} \approx 1.3$ eV$^2$ and $|U_{e4}| \approx 0.1$, even without any assumptions on predicted reactor fluxes. In contrast, the anomalies in the $\nu_e$ appearance channel (dominated by LSND) are in strong tension with improved bounds on $\nu_\mu$ disappearance, mostly driven by MINOS+ and IceCube. Under the sterile neutrino oscillation hypothesis, the p-value for those data sets being consistent is less than $2.6\times 10^{-6}$. Therefore, an explanation of the LSND anomaly in terms of sterile neutrino oscillations in the 3+1 scenario is excluded at the $4.7\sigma$ level. This result is robust with respect to variations in the analysis and used data, in particular it depends neither on the theoretically predicted reactor neutrino fluxes, nor on constraints from any single experiment. Irrespective of the anomalies, we provide updated constraints on the allowed mixing strengths $|U_{\alpha 4}|$ ($\alpha = e,\mu,\tau$) of active neutrinos with a fourth neutrino mass state in the eV range., Comment: 32 pages, 7 figures, 6 tables

The detection of coherent neutrino-nucleus scattering by the COHERENT collaboration has set on quantitative grounds the existence of an irreducible neutrino background in direct detection searches of Weakly Interacting Massive Dark Matter candidates. This background leads to an ultimate discovery limit for these experiments: a minimum Dark Matter interaction cross section below which events produced by the coherent neutrino scattering will mimic the Dark Matter signal, the so-called \emph{neutrino floor}. In this work we study the modification of such neutrino floor induced by non-standard neutrino interactions within their presently allowed values by the global analysis of oscillation and COHERENT data. By using the full likelihood information of such global analysis we consistently account for the correlated effects of non-standard neutrino interactions both in the neutrino propagation in matter and in its interaction in the detector. We quantify their impact on the neutrino floor for five future experiments: DARWIN (Xe), ARGO (Ar), Super-CDMS HV (Ge and Si) and CRESST phase III (CaWO$_4$). Quantitatively, we find that non-standard neutrino interactions allowed at the $3\sigma$ level can result in an increase of the neutrino floor of up to a factor $\sim 5$ with respect to the Standard Model expectations and impact the expected sensitivities of the ARGO, CRESST phase III and DARWIN experiments., Comment: 21 pages, 4 figures. Matches version published in the JHEP. Corrected exposure and results for CRESST phase III

The $\sim 3\sigma$ discrepancy between the predicted and observed reactor anti-neutrino flux, known as the reactor anti-neutrino anomaly, continues to intrigue. The recent discovery of an unexpected bump in the reactor anti-neutrino spectrum, as well as indications that the flux deficit is different for different fission isotopes seems to disfavour the explanation of the anomaly in terms of sterile neutrino oscillations. We critically review this conclusion in view of all available data on electron (anti)neutrino disappearance. We find that the sterile neutrino hypothesis cannot be rejected based on global data and is only mildly disfavored compared to an individual rescaling of neutrino fluxes from different fission isotopes. The main reason for this is the presence of spectral features in recent data from the NEOS and DANSS experiments. If state-of-the-art predictions for reactor fluxes are taken at face value, sterile neutrino oscillations allow a consistent description of global data with a significance close to $3\sigma$ relative to the no-oscillation case. Even if reactor fluxes and spectra are left free in the fit, a $2\sigma$ hint in favour of sterile neutrinos remains, with allowed parameter regions consistent with an explanation of the anomaly in terms of oscillations., Comment: 25 pages, 5 figures. 1 page and table 4 added. Published in JHEP

In the presence of non-standard neutrino interactions (NSI), oscillation data are affected by a degeneracy which allows the solar mixing angle to be in the second octant (aka the dark side) and implies a sign flip of the atmospheric mass-squared difference. This leads to an ambiguity in the determination of the ordering of neutrino masses, one of the main goals of the current and future experimental neutrino program. We show that the recent observation of coherent neutrino--nucleus scattering by the COHERENT experiment, in combination with global oscillation data, excludes the NSI degeneracy at the $3.1\sigma$ ($3.6\sigma$) CL for NSI with up (down) quarks., Comment: 5 pages, 3 figures

In line with its terms of reference the ICFA Neutrino Panel has developed a roadmapfor the international, accelerator-based neutrino programme. A "roadmap discussion document" was presented in May 2016 taking into account the peer-group-consultation described in the Panel's initial report. The "roadmap discussion document" was used to solicit feedback from the neutrino community---and more broadly, the particle- and astroparticle-physics communities---and the various stakeholders in the programme. The roadmap, the conclusions and recommendations presented in this document take into account the comments received following the publication of the roadmap discussion document. With its roadmap the Panel documents the approved objectives and milestones of the experiments that are presently in operation or under construction. Approval, construction and exploitation milestones are presented for experiments that are being considered for approval. The timetable proposed by the proponents is presented for experiments that are not yet being considered formally for approval. Based on this information, the evolution of the precision with which the critical parameters governinger the neutrino are known has been evaluated. Branch or decision points have been identified based on the anticipated evolution in precision. The branch or decision points have in turn been used to identify desirable timelines for the neutrino-nucleus cross section and hadro-production measurements that are required to maximise the integrated scientific output of the programme. The branch points have also been used to identify the timeline for the R&D required to take the programme beyond the horizon of the next generation of experiments. The theory and phenomenology programme, including nuclear theory, required to ensure that maximum benefit is derived from the experimental programme is also discussed.

In presence of non-standard neutrino interactions the neutrino flavor evolution equation is affected by a degeneracy which leads to the so-called LMA-Dark solution. It requires a solar mixing angle in the second octant and implies an ambiguity in the neutrino mass ordering. Non-oscillation experiments are required to break this degeneracy. We perform a combined analysis of data from oscillation experiments with the neutrino scattering experiments CHARM and NuTeV. We find that the degeneracy can be lifted if the non-standard neutrino interactions take place with down quarks, but it remains for up quarks. However, CHARM and NuTeV constraints apply only if the new interactions take place through mediators not much lighter than the electroweak scale. For light mediators we consider the possibility to resolve the degeneracy by using data from future coherent neutrino-nucleus scattering experiments. We find that, for an experiment using a stopped-pion neutrino source, the LMA-Dark degeneracy will either be resolved, or the presence of new interactions in the neutrino sector will be established with high significance., Comment: 33 pages, 9 figures. Minor modifications. Version accepted for publication in JHEP

We compute a new generation of standard solar models (SSMs) that includes recent updates on some important nuclear reaction rates and a more consistent treatment of the equation of state. Models also include a novel and flexible treatment of opacity uncertainties based on opacity kernels, required in the light of recent theoretical and experimental works on radiative opacity. Two large sets of SSMs, each based on a different canonical set of solar abundances with high and low metallicity (Z), are computed to determine model uncertainties and correlations among different observables. We present detailed comparisons of high- and low-Z models against different ensembles of solar observables including solar neutrinos, surface helium abundance, depth of convective envelope and sound speed profile. A global comparison, including all observables, yields a p-value of 2.7$\sigma$ for the high-Z model and 4.7$\sigma$ for the low-Z one. When the sound-speed differences in the narrow region of $0.65 < r/R_{sun} < 0.70$ are excluded from the analysis, results are 0.9$\sigma$ and 3.0$\sigma$ for high- and low-Z models respectively. These results show that: high-Z models agree well with solar data but have a systematic problem right below the bottom of the convective envelope linked to steepness of molecular weight and temperature gradients, and that low-Z models lead to a much more general disagreement with solar data. We also show that, while simple parametrizations of opacity uncertainties can strongly alleviate the solar abundance problem, they are insufficient to substantially improve the agreement of SSMs with helioseismic data beyond that obtained for high-Z models due to the intrinsic correlations of theoretical predictions. All the detailed information of the new solar models, can be found online: http://www.ice.cat/personal/aldos/Solar_Data.html, Comment: 20 pages, 8 figures, 8 table. Accepted in ApJ. All the detailed information of the new solar models is available online: http://www.ice.cat/personal/aldos/Solar_Data.html

Solar neutrino studies triggered and largely motivated the major developments in neutrino physics in the last 50 years. Theory of neutrino propagation in different media with matter and fields has been elaborated. It includes oscillations in vacuum and matter, resonance flavor conversion and resonance oscillations, spin and spin-flavor precession, etc. LMA MSW has been established as the true solution of the solar neutrino problem. Parameters theta12 and Delta_m21^2 have been measured; theta13 extracted from the solar data is in agreement with results from reactor experiments. Solar neutrino studies provide a sensitive way to test theory of neutrino oscillations and conversion. Characterized by long baseline, huge fluxes and low energies they are a powerful set-up to search for new physics beyond the standard 3nu paradigm: new neutrino states, sterile neutrinos, non-standard neutrino interactions, effects of violation of fundamental symmetries, new dynamics of neutrino propagation, probes of space and time. These searches allow us to get stringent, and in some cases unique bounds on new physics. We summarize the results on physics of propagation, neutrino properties and physics beyond the standard model obtained from studies of solar neutrinos., Comment: 16 pages, 6 figures. Typos corrected. Review prepared for the European Physical Journal A (EPJA) issue on "The Solar Neutrinos"

We study the interplay of neutrino oscillation and invisible decay in atmospheric and long-baseline neutrinos experiments. We perform a global analysis of the full atmospheric data from Super-Kamiokande together with long-baseline K2K and MINOS in these scenarios. We find that the admixture of nu_mu -> nu_tau oscillations with parameters Delta_m32^2 = 2.6e-3 eV^2 and theta_23 ~ 34 degrees plus decay of the heavy neutrino, nu_3, with lifetime of the order tau_3/m_3 ~ 2.6e-12 s/eV provides a reasonable fit to atmospheric neutrinos, although this solution becomes more disfavored (dropping to the 99% CL) once long-baseline data are included. Other than this local minimum, the analysis shows no evidence in favor of a non-vanishing neutrino decay width and an lower bound on the decay lifetime tau_3/m_3 > 9.3e-11 s/eV is set at 99% CL. In the framework of Majoron models, this constraint can be translated into a bound on the Majoron coupling to nu_3 and an unmixed very light sterile state, |g_s3| < 8.6e-3 (2.2 eV/m_3)., LaTeX file using elsart style, 10 pages and 2 figures included. Final version

We study the modification of the detected flavor content of ultra high-energy astrophysical neutrinos in the presence of non-standard interactions of neutrinos with the Earth matter. Unlike the case of new physics affecting the propagation from the source to the Earth, non-standard Earth matter effects induce a dependence of the flavor content on the arrival direction of the neutrino. We find that, within the current limits on non-standard neutrino interaction parameters, large deviations from the standard 3-nu oscillation predictions can be expected, in particular for fluxes dominated by one flavor at the source. Conversely they do not give sizable corrections to the expectation of equalized flavors in the Earth for sources dominated by production via pion-muon decay-chain., 12 pages, 6 figures

5 pages, 2 figures.-- PACS nrs.: 14.16.Lm, 15.60.Pq.-- ISI Article Identifier: 000247074600068.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0608319, Printed version published on Jun 22, 2007., Also published in: Proceedings of the 2nd International Conference on Quantum Theories and Renormalization Group in Gravity and Cosmology, Barcelona, July 2006., Precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this contribution, we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates. The extraction is achieved by means of a combination of artificial neural networks as interpolants and Monte Carlo methods.

The precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this contribution we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates., Comment: 4 pages, 3 figs, to appear in the proceedings of the Multi-Messenger Approach to High-Energy Gamma-Ray Sources Conference, Barcelona July 2006

In this talk we discuss the implications that a non-vanishing value of Δ m 21 2 , as indicated by present solar and KamLAND data, has on the analysis of present and future atmospheric neutrino data. This talk is based on the work presented in Ref. [M.C. Gonzalez-Garcia, M. Maltoni, A.Yu. Smirnov, Phys. Rev. D 70 (2004) 093005].

We analyze the impact of recent solar and atmospheric data in the determination of the neutrino oscillation parameters, taking into account that both the solar nu_e and the atmospheric nu_mu may convert to a mixture of active and sterile neutrinos. Furthermore, in the context of the atmospheric neutrino problem we discuss an extended mechanism of neutrino propagation which combines both oscillations and non-standard neutrino-matter interactions. We use the most recent neutrino data, including the 1496-day Super-K solar and atmospheric data samples, the latest SNO spectral and day/night solar data, and the final MACRO atmospheric results. We confirm the clear preference of all the data for pure-active oscillation solutions, bounding the fraction of sterile neutrino involved in oscillations to be less than 52% in the solar sector and less than 40% in the atmospheric sector, at 3 sigma. For the atmospheric case we also derive a bound on the total amount of non-standard neutrino-matter interactions, bounding the flavor-changing component to -0.03, 6 pages, LaTeX file using espcrc2.sty, 1 table and 3 figures included. Talk given at the XXX International Meeting on Fundamental Physics (Jaca, Spain, 28/01-1/02/2002)

We summarize the determination of some neutrino properties from the global analysis of solar, atmospheric, reactor, and accelerator neutrino data in the framework of three-neutrino mixing as well as in some extended scenarios such as the mixing with eV-scale sterile neutrinos invoked for the interpretation of the short baseline anomalies, and the presence of non-standard neutrino interactions., Comment: 16 pages, 7 figures, 2 tables. Review prepared for the Nuclear Physics B Special Issue on "Neutrino Oscillations" celebrating the Nobel Prize in Physics 2015

A global analysis of solar (including the recent SNO result), atmospheric, and reactor neutrino data is presented in terms of three-and four-neutrino oscillations. We first present the allowed regions of solar and atmospheric oscillation parameters assuming three-neutrino families, showing that in this framework it is possible to reconcile the two anomalies and providing an unified fit of all the observables at a time. Then, we consider scenarios where a sterile neutrino is added to the three standard ones and the mass spectra present two separate doublets. We evaluate the allowed active-sterile admixture in both solar and atmospheric oscillations, showing that, although the Super-Kamiokande data disfavor both the pure νμ→νs atmospheric channel and, in combination with SNO, the pure νe→νs solar channel, the result from the combined analysis still favors close-to-pure active and sterile oscillations and disfavors oscillations into a near-maximal active-sterile admixture.

Prompted by recent solar and atmospheric data, we re-analyze the four-neutrino description of current global neutrino oscillation data, including the LSND evidence for oscillations. The higher degree of rejection for non-active solar and atmospheric oscillation solutions implied by the SNO neutral current result as well as by the latest 1489-day Super-K atmospheric neutrino data allows us to rule out (2+2) oscillation schemes proposed to reconcile LSND with the rest of current neutrino oscillation data. Using an improved goodness of fit (gof) method especially sensitive to the combination of data sets we obtain a gof of only 1.6 times 10^{-6} for (2+2) schemes. Further, we re-evaluate the status of (3+1) oscillations using two different analyses of the LSND data sample. We find that also (3+1) schemes are strongly disfavoured by the data. Depending on the LSND analysis we obtain a gof of 5.6 times 10^{-3} or 7.6 times 10^{-5}. This leads to the conclusion that all four-neutrino descriptions of the LSND anomaly, both in (2+2) as well as (3+1) realizations, are highly disfavoured. Our analysis brings the LSND hint to a more puzzling status., 21 pages, 7 figures

We present a global analysis of solar, atmospheric, reactor and accelerator neutrino data in the framework of three-neutrino oscillations based on data available in summer 2014. We provide the allowed ranges of the six oscillation parameters and show that their determination is stable with respect to uncertainties related to reactor neutrino and solar neutrino flux predictions. We find that the maximal possible value of the Jarlskog invariant in the lepton sector is $0.0329 \pm 0.0009$ ($\pm 0.0027$) at the $1\sigma$ ($3\sigma$) level and we use leptonic unitarity triangles to illustrate the ability of global oscillation data to obtain information on CP violation. We discuss "tendencies and tensions" of the global fit related to the octant of $\theta_{23}$ as well as the CP violating phase $\delta_\mathrm{CP}$. The favored values of $\delta_\mathrm{CP}$ are around $3\pi/2$ while values around $\pi/2$ are disfavored at about $\Delta\chi^2 \simeq 6$. We comment on the non-trivial task to assign a confidence level to this $\Delta\chi^2$ value by performing a Monte Carlo study of T2K data., Comment: 28 pages, 10 figures, 1 table. Typos corrected. Updated results of the global fit will be available at http://www.nu-fit.org/

We discuss the current status of neutrino oscillations in models with more than three light neutrino flavors. In particular, we present results of a global fit to short and long baseline oscillation data from reactor, accelerator, atmospheric, solar, and radioactive source experiments. We examine to what extent experimental hints for oscillations involving sterile neutrinos—in particular the reactor and gallium anomalies as well as the MiniBooNE and LSND results—are compatible with null results from other experiments. In all cases, we find severe tension in the global fit, which leads us to the conclusion that models augmenting the Standard Model only by one or several eV-scale sterile neutrinos are unable to explain all short-baseline anomalies simultaneously.

In this talk we present the update (including the recent SNO results) of our analysis of the neutrino oscillation solutions of the solar and atmospheric neutrino problems in the framework of four-neutrino mixing where a sterile neutrino is added to the three standard ones and the mass spectra present two separated doublets. Such scenarios allow for simultaneous transitions of solar $\nu_e$, as well as atmospheric $\nu_\mu$, into a combination of active and sterile neutrinos. We evaluate the allowed active-sterile admixture in both solar and atmospheric oscillations from the combined analysis. Our results show that, although the Super-Kamiokande data disfavour both the pure $\nu_\mu\to\nu_s$ atmospheric channel and, in combination with SNO, the pure $\nu_e\to\nu_s$ solar channel, the result from the combined analysis still favours close-to-pure active and sterile oscillations and disfavours oscillations into a near-maximal active-sterile admixture.

Using the computer code CompHEP we estimate the number of events and the background, at LEP II and TESLA, for the reaction $e^+ e^- \to N\bar{N}\gamma$, where $N$ is a hypothetical Dirac neutrino with mass of the order of 50 GeV., Comment: Standard LaTeX, 9 pages, 2 tables, 3 figures