Presence Of Sterile Neutrinos Research Articles

θ23 Octant sensitivity in presence of light sterile and active ν and [formula omitted] oscillations using beamline experiments

We examine the octant sensitivity of the long-baseline neutrino oscillation experiments in view of light sterile neutrino flavors with masses in the 1 eV range. Considering the active-sterile mixing, we explore the possible preferred running modes either neutrino or anti-neutrino for a long-baseline experiment to avoid the octant degeneracy and will show the θ23 sensitivity for different values of active and sterile neutrino phase angles. We simulated different Long baseline experiments for the different possible combinations of mixing angles and phases and will show whether an experiment can probe the right octant in presence of sterile neutrino by choosing the suitable beam either in neutrino or antineutrino running mode.

Impact of CP violation searches at MOMENT experiment with sterile neutrino

We examine the scope of the MOMENT experiment in the context of CP violation searches with the presence of extra eV scale sterile neutrino. MOMENT is a proposed medium baseline neutrino oscillation experiment using muon beams for neutrinos production, making it advantageous over π0 background and other technical difficulties. We work over the first oscillation maxima which matches the peak value of flux with a run time of 5 years for both neutrino and anti-neutrino modes. We perform the bi-probability studies for both 3 and 3+1 flavor mixing schemes. The CP violation sensitivities arising from the fundamental CP phase δ13 and unknown CP phase δ14 are explored at the firm footing. Slight deteriorations are observed in CP violations induced by δ13 as the presence of sterile neutrino is considered. We also look at the reconstruction of CP violations phases δ13 and δ14 and the MOMENT experiment shows significant capabilities in the precise measurement of δ13 phase.

Sterile neutrinos: propagation in matter and sensitivity to sterile mass ordering

We analytically calculate the neutrino conversion probability Pμe in the presence of sterile neutrinos, with exact dependence on Delta {m}_{41}^2 and with matter effects explicitly included. Using perturbative expansion in small parameters, the terms involving the small mixing angles θ24 and θ34 can be separated out, with θ34 dependence only arising due to matter effects. We express Pμe in terms of the quantities of the form sin(x)/x, which helps in elucidating its dependence on matter effects and a wide range of Delta {m}_{41}^2 values. Our analytic expressions allow us to predict the effects of the sign of Delta {m}_{41}^2 at a long baseline experiment like DUNE. We numerically calculate the sensitivity of DUNE to the sterile mass ordering and find that this sensitivity can be significant in the range mid Delta {m}_{41}^2mid sim left({10}^{-4}-{10}^{-2}right) eV2, for either mass ordering of active neutrinos. The dependence of this sensitivity on the value of Delta {m}_{41}^2 for all mass ordering combinations can be explained by investigating the resonance-like terms appearing due to the interplay between the sterile sector and matter effects.

Light sterile neutrinos and lepton-number-violating kaon decays in effective field theory

We investigate lepton-number-violating decays K∓ → π±l∓l∓ in the presence of sterile neutrinos. We consider minimal interactions with Standard-Model fields through Yukawa couplings as well as higher-dimensional operators in the framework of the neutrino-extended Standard Model Effective Field Theory. We use SU(3) chiral perturbation theory to match to mesonic interactions and compute the lepton-number-violating decay rate in terms of the neutrino masses and the Wilson coefficients of higher-dimensional operators. For neutrinos that can be produced on-shell, the decay rates are highly enhanced and higher-dimensional interactions can be probed up to very high scales around mathcal{O} (30) TeV.

Exploring the new physics phases in 3+1 scenario in neutrino oscillation experiments

The various global analyses of available neutrino oscillation data indicate the presence of the standard 3 + 0 neutrino oscillation picture. However, there are a few short baseline anomalies that point to the possible existence of a fourth neutrino (with mass in the eV-scale), essentially sterile in nature. Should sterile neutrino exist in nature and its presence is not taken into consideration properly in the analyses of neutrino data, the interference terms arising due to the additional CP phases in presence of a sterile neutrino can severely impact the physics searches in long baseline (LBL) neutrino oscillation experiments. In the current work we consider one light (eV-scale) sterile neutrino and probe all the three CP phases (δ13, δ24, δ34) in the context of the upcoming Deep Underground Neutrino Experiment (DUNE) and also estimate how the results improve when data from NOvA, T2K and T2HK are added in the analysis. We illustrate the ∆χ2 correlations of the CP phases among each other, and also with the three active-sterile mixing angles. Finally, we briefly illustrate how the relevant parameter spaces in the context of neutrinoless double beta decay get modified in light of the bounds in presence of a light sterile neutrino.

Sterile neutrinos and neutrinoless double beta decay in effective field theory

We investigate neutrinoless double beta decay (0νββ) in the presence of sterile neutrinos with Majorana mass terms. These gauge-singlet fields are allowed to interact with Standard-Model (SM) fields via renormalizable Yukawa couplings as well as higher-dimensional gauge-invariant operators up to dimension seven in the Standard Model Effective Field Theory extended with sterile neutrinos. At the GeV scale, we use Chiral effective field theory involving sterile neutrinos to connect the operators at the level of quarks and gluons to hadronic interactions involving pions and nucleons. This allows us to derive an expression for 0νββ rates for various isotopes in terms of phase-space factors, hadronic low-energy constants, nuclear matrix elements, the neutrino masses, and the Wilson coefficients of higher-dimensional operators. The required hadronic low-energy constants and nuclear matrix elements depend on the neutrino masses, for which we obtain interpolation formulae grounded in QCD and chiral perturbation theory that improve existing formulae that are only valid in a small regime of neutrino masses. The resulting framework can be used directly to assess the impact of 0νββ experiments on scenarios with light sterile neutrinos and should prove useful in global analyses of sterile-neutrino searches. We per- form several phenomenological studies of 0νββ in the presence of sterile neutrinos with and without higher-dimensional operators. We find that non-standard interactions involving sterile neutrinos have a dramatic impact on 0νββ phenomenology, and next-generation experiments can probe such interactions up to scales of mathcal{O} (100) TeV.

Sterile neutrinos with altered dispersion relations revisited

In this paper we investigate neutrino oscillations with altered dispersion relations in the presence of sterile neutrinos. Modified dispersion relations represent an agnostic way to parameterize new physics. Models of this type have been suggested to explain global neutrino oscillation data, including deviations from the standard three-neutrino paradigm as observed by a few experiments. We show that, unfortunately, in this type of models new tensions arise turning them incompatible with global data.

Degeneracy Resolution Capabilities of NOνA and DUNE in the Presence of Light Sterile Neutrino

We investigate the implications of a sterile neutrino on the physics potential of the proposed experiment DUNE and future runs of NOνA using latest NOνA results. Using combined analysis of the disappearance and appearance data, NOνA reported preferred solutions at normal hierarchy (NH) with two degenerate best-fit points: one in the lower octant (LO) and δ13 = 1.48π and the other in higher octant (HO) and δ13 = 0.74π. Another solution of inverted hierarchy (IH), which is 0.46σ away from best fit, was also reported. We discuss chances of resolving these degeneracies in the presence of sterile neutrino.

Prospects for detecting eV-scale sterile neutrinos from a galactic supernova

Future neutrino detectors will obtain high-statistics data from a nearby core-collapse supernova. We study the mixing with eV-mass sterile neutrinos in a supernova environment and its effects on the active neutrino fluxes as detected by Hyper-Kamiokande and IceCube. Using a Markov Chain Monte Carlo analysis, we make projections for how accurately these experiments will measure the active-sterile mixing angle θs given that there are substantial uncertainties on the expected luminosity and spectrum of active neutrinos from a galactic supernova burst. We find that Hyper-Kamiokande can reconstruct the sterile neutrino mixing and mass in many different situations, provided the neutrino luminosity of the supernova is known precisely. Crucially, we identify a degeneracy between the mixing angle and the overall neutrino luminosity of the supernova. This means that it will only be possible to determine the luminosity if the presence of sterile neutrinos with θs ≳ 0.1̂ can be ruled out independently. We discuss ways in which this degeneracy may be broken in the future.

Recent Borexino results and perspectives of the SOX measurement

Borexino is a liquid scintillator detector sited underground in the Laboratori Nazionali del Gran Sasso (Italy). Its physics program, until the end of this year, is focussed on the study of solar neutrinos, in particular from the Beryllium, pp, pep and CNO fusion reactions. Knowing the reaction chains in the sun provides insights towards physics disciplines such as astrophysics (star physics, star formation, etc.), astroparticle and particle physics. Phase II started in 2011 and its aim is to improve the phase I results, in particular the measurements of the neutrino fluxes from the pep and CNO processes. By the end of this year, data taking from the sun will be over and a new project is scheduled to launch: Short distance Oscillation with boreXino (SOX), which uses a Cerium source for neutrinos (100÷150 kCi of activity) and aims to confirm or rule out the presence of sterile neutrinos. This particle is hypothesised to justify the reactor, Gallium and LSND anomalies found and can reject extensions to the standard model. The work presented is a summary of the solar neutrino results achieved so far, which lead not only to a precise study of the processes in the sun, but also to more Standard Model oriented measurements (such as the stability of the charge, i.e. the life time of the electron). Furthermore, the perspectives of the SOX program are discussed showing the experiment sensitivity to a fourth neutrino state covering almost entirely 3σ of the preferred region of the anomalous neutrino experiments, and additional applications of the detector such as the study of geo-neutrinos.

Can we probe intrinsic CP and T violations and nonunitarity at long baseline accelerator experiments?

One of the fundamental parameters entering neutrino oscillation framework is the leptonic CP phase $\delta_{13}$ and its measurement is an important goal of the planned long baseline experiments. It should be noted that ordinary matter effects complicate the determination of this parameter and there are studies in literature that deal with separation of intrinsic versus extrinsic CP violation. It is important to investigate the consequences of new physics effects that can not only hamper the measurement of $\delta_{13}$, but also impact the consequences of discrete symmetries such as CP, T and unitarity in different oscillation channels. In the present work, we explore these discrete symmetries and implications on unitarity in presence of two new physics scenarios (non-standard interaction in propagation and presence of sterile neutrinos) that serve as good examples of going beyond the standard scenario in different directions. We uncover the impact of new physics scenarios on disentangling intrinsic and extrinsic CP violation.

Probing light sterile neutrinos in medium baseline reactor experiments

Medium-baseline reactor experiments (Double Chooz, Daya Bay and RENO) provide a unique opportunity to test the presence of light sterile neutrinos. We analyze the data of these experiments in the search of sterile neutrinos and also test the robustness of ${\ensuremath{\theta}}_{13}$ determination in the presence of sterile neutrinos. We show that existence of a light sterile neutrino state improves the fit to these data moderately. We also show that the measured value of ${\ensuremath{\theta}}_{13}$ by these experiments is reliable even in the presence of sterile neutrinos, and the reliability owes significantly to the Daya Bay and RENO data. From the combined analysis of the data of these experiments, we constrain the mixing of a sterile neutrino with $\ensuremath{\Delta}{m}_{41}^{2}\ensuremath{\sim}({10}^{\ensuremath{-}3}--{10}^{\ensuremath{-}1})\text{ }\text{ }{\mathrm{eV}}^{2}$ to ${sin}^{2}2{\ensuremath{\theta}}_{14}\ensuremath{\lesssim}0.1$ at 95% C.L.

A proposed search for sterile neutrinos with the ICARUS detector at the CERN-PS

An experiment to search for sterile neutrinos beyond the Standard Model with the CERN-PS 19.2 GeV beam and the technology of imaging in ultra-pure cryogenic liquid Argon is proposed. The superior quality of the LAr-TPC, now widely demonstrated experimentally and in particular its unique e/π0 discrimination allows a full rejection of backgrounds, offers the possibility to explore the neutrino conversion into sterile components as recently suggested by the analysis of different observed neutrino anomalies.The experiment is based on two identical LAr-TPC detectors observing the electron-neutrino signal in the Near and Far positions, the first of about 150 tons at 127 m from the proton target, the second one of about 600 tons placed 850 m away. This project will exploit the largest LAr-TPC ever built, ICARUS T600 now running underground at LNGS exposed to CNGS neutrino beam, by moving it from Gran Sasso to the CERN Far position. An additional 150 t detector will be constructed in the Near position. The intrinsic νE beam spectra are expected practically identical in the two positions; in addition all cross-sections and experimental biases cancel out in the comparison of the two detector signals allowing to perform a sensitive search for neutrino oscillations in the presence of sterile neutrinos.

Sterile neutrinos and IceCube

Although the framework for oscillations of the three neutrino flavors in the Standard Model has been convincingly established, indications persist that it may be incomplete. Challenges are coming from the LSND and MiniBooNe short-baseline experiments, from the neutrino sources used in the Gallex and Sage solar neutrino experiments and, more recently, from an a-posteriori analysis of reactor neutrino experiments. One way to accommodate the reported "anomalies", if real, is to introduce one or more sterile neutrinos in the mass range δm2 ~ 1eV2. TeV atmospheric neutrinos propagating through the Earth undergo resonant oscillations in the presence of sterile neutrinos; a clear signature in a neutrino telescope like IceCube is the the change in shape of the zenith-energy distribution of the atmospheric neutrinos.IceCube detects more than 100,000 atmospheric neutrinos per year. Statistics do not limit such a measurement, but the uncertainties in modeling the expectations of the conventional 3-flavor scenario, including the systematics of the detector, do. We review the status and future perspectives of understanding the zenith and energy response of IceCube in the TeV energy range.

Tree-level lepton universality violation in the presence of sterile neutrinos: impact for R K and R π

Abstract We consider a tree-level enhancement to the violation of lepton flavour universality in light meson decays arising from modified Wℓν couplings in the standard model minimally extended by sterile neutrinos. Due to the presence of additional mixings between the active (left-handed) neutrinos and the new sterile states, the deviation from unitarity of the leptonic mixing matrix intervening in charged currents might lead to a tree-level enhancement of R P = Γ(P → eν)/Γ(P → μν), with P = K, π. We illustrate these enhancements in the case of the inverse seesaw model, showing that one can saturate the current experimental bounds on Δr K (and Δr π ), while in agreement with the different experimental and observational constraints.

Implications of sterile neutrinos for medium/long-baseline neutrino experiments and the determination ofθ13

We revisit some of the recent neutrino observations and anomalies in the context of sterile neutrinos. Based on a general parametrization motivated in the presence of sterile neutrinos, the consistency of the MINOS disappearance data with additional sterile neutrinos is discussed. We also explore the implications of sterile neutrinos for the measurement of $|U_{\mu3}|$ in this case. Regarding the determination of $|U_{e3}|$, we observe that the existence of sterile neutrinos may induce a significant modification of the $\theta_{13}$ angle in neutrino appearance experiments like T2K and MINOS, over and above the ambiguities and degeneracies that are already present in 3-neutrino parameter extractions. The modification is less significant in reactor neutrino experiments like Double-CHOOZ, Daya Bay and RENO and therefore the extracted $|U_{e3}|$ value when sterile neutrinos are present is close to the one that would be obtained in the 3-neutrino case. We also conclude that the results from T2K imply a 90% C.L. lower-bound on $|U_{e3}|$, in the "$\,3+2$" neutrino case, which is still within the sensitivity of future reactor neutrino experiments like Daya Bay, and consistent with the one-$\sigma$ range of $\sin^22\theta_{13}$ recently reported by the Double-CHOOZ experiment. Finally, we argue that for the recently determined best-fit parameters, the results in the "$\,3+1$" scenario would be very close to the medium/long baseline results obtained in the "$\,3+2$" case analyzed in this work.

Impact of eV-mass sterile neutrinos on neutrino-driven supernova outflows

Motivated by recent hints for sterile neutrinos from the reactor anomaly, we study active-sterile conversions in a three-flavor scenario (2 active + 1 sterile families) for three different representative times during the neutrino-cooling evolution of the proto-neutron star born in an electron-capture supernova. In our ``early model'' (0.5 s post bounce), the νe-νs MSW effect driven by Δm2 = 2.35eV2 is dominated by ordinary matter and leads to a complete νe-νs swap with little or no trace of collective flavor oscillations. In our ``intermediate'' (2.9 s p.b.) and ``late models'' (6.5 s p.b.), neutrinos themselves significantly modify the νe-νs matter effect, and, in particular in the late model, νν refraction strongly reduces the matter effect, largely suppressing the overall νe-νs MSW conversion. This phenomenon has not been reported in previous studies of active-sterile supernova neutrino oscillations. We always include the feedback effect on the electron fraction Ye due to neutrino oscillations. In all examples, Ye is reduced and therefore the presence of sterile neutrinos can affect the conditions for heavy-element formation in the supernova ejecta, even if probably not enabling the r-process in the investigated outflows of an electron-capture supernova. The impact of neutrino-neutrino refraction is strong but complicated, leaving open the possibility that with a more complete treatment, or for other supernova models, active-sterile neutrino oscillations could generate conditions suitable for the r-process.

Light sterile neutrinos: models and phenomenology

Motivated by recent hints in particle physics and cosmology, we study the realization of eV-scale sterile neutrinos within both the seesaw mechanism and flavor symmetry theories. We show that light sterile neutrinos can rather easily be accommodated in the popular A_4 flavor symmetry models. The exact tri-bimaximal mixing pattern is perturbed due to active-sterile mixing, which we discuss in detail for one example. In addition, we find an interesting extension of the type I seesaw, which can provide a natural origin for eV-scale sterile neutrinos as well as visible admixtures between sterile and active neutrinos. We also show that the presence of sterile neutrinos would significantly change the observables in neutrino experiments, specifically the oscillation probabilities in short-baseline experiments and the effective mass in neutrino-less double beta decay. The latter can prove particularly helpful to strengthen the case for eV-scale sterile neutrinos.

Neutrinos from CNO cycle at the present epoch of the solar neutrino research

The CNO cycle contributes only a small fraction to the energy generated in the Sun but there’s still no experimental data on exactly how small this contribution is. After the results of Borexino experiment the CNO neutrinos it is the last missing chain to compose the total picture of the energy generation of the Sun. To get precision in the evaluation of the flux of pp-neutrinos one needs to measure the flux of CNO neutrinos. Then it will be possible to address the question on the presence of still unknown (hidden) sources of solar energy and/or on the presence of sterile neutrinos. The future experimental program to measure the effect from CNO neutrinos is discussed.

Confusing sterile neutrinos with deviation from tribimaximal mixing at neutrino telescopes

We expound on the impact of extra sterile species on the ultra high energy neutrino fluxes in neutrino telescopes. We use three types of well-known flux ratios and compare the values of these flux ratios in the presence of sterile neutrinos, with those predicted by deviation from the tribimaximal mixing scheme. We show that in the upcoming neutrino telescopes, it is easy to confuse the signature of sterile neutrinos with that of the deviation from tribimaximal mixing. We also show that if the measured flux ratios acquire a value well outside the range predicted by the standard scenario with three active neutrinos only, it might be possible to tell the presence of extra sterile neutrinos by observing ultra high energy neutrinos in future neutrino telescopes.