Neutrino Framework Research Articles

The violation of equivalence principle and four neutrino oscillations for long baseline neutrinos

Violation of equivalence principle predicts that neutrinos of different flavor couple differently with gravity. Such a scenario can give rise to gravity induced flavor oscillations in addition to the usual mass flavor neutrino oscillations during the neutrino propagation. Even if the equivalence principle is indeed violated, their measure will be extremely small. We explore the possibility to probe the violation of equivalence principle (VEP) for the case of long baseline (LBL) neutrinos in a 4-flavor neutrino framework (3 active + 1 sterile) where both mass and gravity induced oscillations are considered. To this end, we have explicitly calculated the oscillation probability in 4-flavor framework that includes in addition to the mass-flavor mixing in matter, the gravity-flavor mixing also. The energy eigenvalues are then obtained by diagonalizing such a 4-flavor mixing matrix. The formalism is then employed to estimate the wrong and right sign muon yields at a far detector for neutrinos produced in a neutrino factory and travel through the Earth matter. These results are compared with the similar estimations when the usual three active neutrinos are considered.

Flavor-specific interaction favors strong neutrino self-coupling in the early universe

Flavor-universal neutrino self-interaction has been shown to ease the tension between the values of the Hubble constant measured from early and late Universe data. We introduce a self-interaction structure that is flavor-specific in the three active neutrino framework. This is motivated by the stringent constraints on new secret interactions among electron and muon neutrinos from several laboratory experiments. Our study indicates the presence of a strongly interaction mode which implies a late-decoupling of the neutrinos just prior to matter radiation equality. Using the degeneracy of the coupling strength with other cosmological parameters, we explain the origin of this new mode as a result of better fit to certain features in the CMB data. We find that if only one or two of the three active neutrino flavors are interacting, then the statistical significance of the strongly-interacting neutrino mode increases substantially relative to the flavor-universal scenario. However, the central value of the coupling strength for this interaction mode does not change by any appreciable amount in the flavor-specific cases. We also briefly analyze a scenario with more than three neutrino species of which only one is self-interacting. In none of the cases, we find a large enough Hubble constant that could resolve the so-called Hubble tension.

CPT Violation in Four Flavor Neutrino Framework from Planck Scale Effects

The neutrino mass squared difference determine from the experimental solar neutrino data and ant-neutrino mass squared difference determine from the KamLAND reactor experiment. The best fit central value of the two case differ from each other by about $\left |{\Delta }_{21}-\bar {\Delta }_{21}\right |=$ 10− 5eV2and angle $\left |\theta _{12}-\bar {\theta }_{12}\right |=2^{0}$ in the mixing angle. CPT invariantindicates that the oscillation parameters for neutrino and anti-neutrino are to be identical. The non-zero difference between neutrino and ant-neutrino oscillation parameter and it provides a signal for CPT violation. Using this approach, we discuss the CPT violation in four flavor neutrino framework from Planck scale effects. We find that the non zero values of differencebetween mass squared $\left |{\Delta }_{ij}^{\prime }-\bar {\Delta }^{\prime }_{ij}\right |$ and mixing angles $\left |\theta _{ij}^{\prime }-\bar {\theta }^{\prime }_{ij}\right |$ of neutrinos and ant-neutrinos.

Sensitivity to sterile neutrino mixing using reactor antineutrinos

The reactor antineutrinos are used for the precise measurement of oscillation parameters in the 3-neutrino model, and also used to investigate active-sterile neutrino mixing sensitivity in the 3+1 neutrino framework. In the present work, we study the feasibility of sterile neutrino search with the indian scintillator matrix for reactor anti-neutrino (ISMRAN) experimental set-up using electron antineutrinos ({overline{nu }}_e) produced from reactor as a source. The so-called 3+1 scenario is considered for active-sterile neutrino mixing, which leads to projected exclusion curves in the sterile neutrino mass and mixing angle plane. The analysis is performed considering both the reactor and detector related parameters. It is found that, the ISMRAN set-up can observe the active-sterile neutrino mixing sensitivity for sin ^{2}2theta _{14} ge 0.064 and varDelta m^{2}_{41} = 1.0hbox {eV}^2 at 90% confidence level for an exposure of 1 ton-year by using neutrinos produced from the DHRUVA reactor with thermal power of 100 hbox {MW}_{{th}}. It is also observed that, there is a significant improvement of the active-sterile neutrino mixing parameter sin ^{2}2theta _{14} to sim 0.03 at the same varDelta m^{2}_{41} by putting the ISMRAN detector set-up at a distance of 20 m from the compact proto-type fast breeder reactor facility with thermal power of 1250 hbox {MW}_{{th}}.

A short travel for neutrinos in Large Extra Dimensions

Neutrino oscillations successfully explain the flavor transitions observed in neutrinos produced in natural sources like the center of the sun and the earth atmosphere, and also from man-made sources like reactors and accelerators. These oscillations are driven by two mass-squared differences, solar and atmospheric, at the sub-eV scale. However, longstanding anomalies at short-baselines might imply the existence of new oscillation frequencies at the eV-scale and the possibility of this sterile state(s) to mix with the three active neutrinos. One of the many future neutrino programs that are expected to provide a final word on this issue is the Short-Baseline Neutrino Program (SBN) at FERMILAB. In this letter, we consider a specific model of Large Extra Dimensions (LED) which provides interesting signatures of oscillation of extra sterile states. We started re-creating sensitivity analyses for sterile neutrinos in the 3+1 scenario, previously done by the SBN collaboration, by simulating neutrino events in the three SBN detectors from both muon neutrino disappearance and electron neutrino appearance. Then, we implemented neutrino oscillations as predicted in the LED model and also we have performed sensitivity analysis to the LED parameters. Finally, we studied the SBN power of discriminating between the two models, the 3+1 and the LED. We have found that SBN is sensitive to the oscillations predicted in the LED model and have the potential to constrain the LED parameter space better than any other oscillation experiment for m1D < 0.1 eV. In case SBN observes a departure from the three active neutrino framework, it also has the power of discriminating between sterile oscillations predicted in the 3+1 framework and the LED ones.

Probing direct and indirect unitarity violation in future accelerator neutrino facilities

The possible existence of light and heavy sterile neutrinos may give rise to direct and indirect unitarity violation of the 3×3 lepton mixing matrix respectively. In the current work we study the potential of future accelerator neutrino facilities in probing the unitarity violation effects. Taking DUNE, T2HK and a low-energy Neutrino Factory (LENF) as working examples of future accelerator neutrino facilities, we study the distinct effects of direct and indirect unitarity violation on the discovery reach of the leptonic CP violation and precision measurements of θ23 in the three neutrino framework. In addition, constraints on the additional mixing parameters of direct and indirect unitarity violation are also discussed. Finally, we stress that the combination of experiments with different oscillation channels, different neutrino beams and different detector techniques will be an effective solution to the parameter degeneracy problem and give the robust measurement of leptonic CP violation even if the direct and indirect unitarity violation are taken into account.

Determination of the neutrino mass hierarchy with a new statistical method

Nowadays neutrino physics is undergoing a change of perspective: the discovery period is almost over and the phase of precise measurements is starting. Despite the limited statistics collected for some variables, the three--flavour oscillation neutrino framework is strengthening well. In this framework a new method has been developed to determine the neutrino mass ordering, one of the still unknown and most relevant parameters. The method is applied to the 2015 results of the NOvA experiment for $\nu_\mu \rightarrow \nu_e$ appearance, including its systematic errors. A substantial gain in significance is obtained compared to the traditional $\Delta\chi^2$ approach. Perspectives are provided for future results obtainable by NOvA with larger exposures. Assuming the number of the 2015 $\nu_e$ observed events scales with the exposure, an increase in only a factor three would exclude the inverted hierarchy at more than 95\% C.L. over the full range of the CP violating phase. The preliminary 2016 NOvA measurement on \numunue appearance has also been analyzed.

The next challenge for neutrinos: the mass ordering

Neutrino physics is nowadays receiving more and more attention as a possible source of information for the long--standing investigation of new physics beyond the Standard Model. This is also supported by the recent change of perspectives in neutrino researches since the discovery period is almost over and we are entering the phase of precise measurements. Despite the limited statistics collected for some variables, the three--flavour neutrino framework seems well strengthening. However some relevant pieces of this framework are still missing. The amount of a possible CP violation phase and the mass ordering are among the most challenging and probably those that will be known in the near future. In this paper we will discuss these two correlated issues and a very recent new statistical method introduced to get reliable results on the mass ordering.

Large extra dimensions at the Deep Underground Neutrino Experiment

We investigate the potential of the long-baseline Deep Underground Neutrino Experiment (DUNE) to study large-extra-dimension (LED) models originally proposed to explain the smallness of neutrino masses by postulating that right-handed neutrinos, unlike all standard model fermion fields, can propagate in the bulk. The massive Kaluza-Klein (KK) modes of the right-handed neutrino fields modify the neutrino oscillation probabilities and can hence affect their propagation. We show that, as far as DUNE is concerned, the LED model is indistinguishable from a $(3 + 3N)$-neutrino framework for modest values of $N$; $N$ = 1 is usually a very good approximation. Nonetheless, there are no new sources of $CP$-invariance violation other than one $CP$-odd phase that can be easily mapped onto the $CP$-odd phase in the standard three-neutrino paradigm. We analyze the sensitivity of DUNE to the LED framework, and explore the capability of DUNE to differentiate the LED model from the three-neutrino scenario and from a generic $(3 + 1)$-neutrino model.

EXTRINSIC CPT VIOLATION WITH STERILE NEUTRINO

In this work, the matter induced CPT violating effects in neutrino oscillations are quantified with the help of Neutrino Factory setup. Here this extrinsic CPT violation is checked for the disappearance channel (ߥ ఓ → ߥ ఓ). The information of extrinsic CPT violation will help us in investigating pure CPT violation. The profile of interior density of earth from which the neutrinos passes is considered as step function matter density profile (PREM) in the present work. In the considered (3+1) neutrino framework, extrinsic CPT violation is checked for baselines 1300 km – 7500 km for energy range 4 to 50 GeV. In order to check sterile contribution in the total extrinsic CPT violation, we have selected few observables which can disentangle the contributions arising due to the presence of sterile neutrino from those which arises due to the presence of three active neutrinos. In the presence of sterile neutrino these observables promote higher energies (more than 20 GeV) especially 15 GeV for long baseline experiments to probe pure(intrinsic) CPT violation because sterile contribution to extrinsic CPT violation becomes very less at these energies. To give a realistic estimate of extrinsic CPT violation, the product of sterile angles ߠ ଶସ and ߠ ଷସ is constrained in our analysis. We get ߠ ଶସ .ߠ ଷସ≳ 0.006 rad 2 with liquid argon detector and ߠ ଶସ .ߠ ଷସ≳ 0.007 rad 2 with magnetized iron detector at 90% C.L. for the

Search for sterile neutrino mixing in the muon neutrino to tau neutrino appearance channel with the OPERA detector

The OPERA experiment observed νμ → ντ oscillations in the atmospheric sector. To this purpose the hybrid OPERA detector was exposed to the CERN Neutrinos to Gran Sasso beam from 2008 to 2012, at a distance of 730 km from the neutrino source. Charged-current interactions of ντ were searched for through the identification of τ lepton decay topologies. The five observed ντ interactions are consistent with the expected number of events in the standard three neutrino framework. Based on this result, new limits on the mixing parameters of a massive sterile neutrino may be set. Preliminary results of the analysis performed in the 3+1 neutrino framework are here presented.

Beyond six parameters: ExtendingΛCDM

Cosmological constraints are usually derived under the assumption of a $6$ parameters $\Lambda$-CDM theoretical framework or simple one-parameter extensions. In this paper we present, for the first time, cosmological constraints in a significantly extended scenario, varying up to $12$ cosmological parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the dark energy equation of state, the gravitational waves background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization) we found no significant indication for extensions to the standard $\Lambda$-CDM scenario, with the notable exception of the angular power spectrum lensing amplitude, $A_{\rm lens}$ that is larger than the expected value at more than two standard deviations even when combining the Planck data with BAO and supernovae type Ia external datasets. In our extended cosmological framework, we find that a combined Planck+BAO analysis constrains the value of the r.m.s. density fluctuation parameter to $\sigma_8=0.781_{-0.063}^{+0.065}$ at $95 \%$ c.l., helping to relieve the possible tensions with the CFHTlenS cosmic shear survey. We also find a lower value for the reionization optical depth $\tau=0.058_{-0.043}^{+0.040}$ at $95$ \% c.l. respect to the one derived under the assumption of $\Lambda$-CDM. The scalar spectral index $n_S$ is now compatible with a Harrison-Zeldovich spectrum to within $2.5$ standard deviations. Combining the Planck dataset with the HST prior on the Hubble constant provides a value for the equation of state $w < -1$ at more than two standard deviations while the neutrino effective number is fully compatible with the expectations of the standard three neutrino framework.

CP AND T VIOLATION AT LONG BASELINE EXPERIMENTS

Existing Universe is matter dominated. Baryonic matter and leptonic matter asymmetry is one of the profound mystries in particle physics. The CP violation can elucidate the above mystery. Extent of bound, neutrino experiments can impose on CP violation will enlighten the path of particle physicist to go beyond the standard model. The matter effect in itself give rise to CP variance therefore looking for T violation will reinforce our predictions. Atmospheric neutrino mass difference is found to be around 10 -3 ~ 10 -2 eV 2 . In order to make meaningful predictions with such small ∆m 2 , baseline of the order of 1000 Km to 100 Km for a neutrino of energy 1 GeV is required. In this work we have studied the menifestation of CP and T violation with the help of different proposed long baseline experiments for three neutrino framework.

Velocity-induced neutrino oscillation and its possible implications for long baseline neutrinos

If the three types of active neutrinos possess different maximum attainable velocities and the neutrino eigenstates in the velocity basis are different from those in the flavor (and mass) basis, then this will induce a flavor oscillation in addition to the normal mass-flavor oscillation. Here we study such an oscillation scenario in three neutrino framework including also the matter effect and apply our results to demonstrate its consequences for long baseline (LBL) neutrinos. We also predict the possible signatures in terms of yields in a possible LBL neutrino experiment.

Exact and approximate formulas for neutrino mixing and oscillations with non-standard interactions

We present, both exactly and approximately, a complete set of mappings between the vacuum (or fundamental) leptonic mixing parameters and the effective ones in matter with non-standard neutrino interaction (NSI) effects included. Within the three-flavor neutrino framework and a constant matter density profile, a full set of sum rules is established, which enables us to reconstruct the moduli of the effective leptonic mixing matrix elements, in terms of the vacuum mixing parameters in order to reproduce the neutrino oscillation probabilities for future long-baseline experiments. Very compact, but quite accurate, approximate mappings are obtained based on series expansions in the neutrino mass hierarchy parameter η ≡ Δm221/Δm231, the vacuum leptonic mixing parameter s13 ≡ sin θ13, and the NSI parameters eαβ. A detailed numerical analysis about how the NSIs affect the smallest leptonic mixing angle θ13, the deviation of the leptonic mixing angle θ23 from its maximal mixing value, and the transition probabilities useful for future experiments are performed using our analytical results.

Implications of neutrino data circa 2005

Adopting the 3 neutrino framework, we present an updated determination of the oscillation parameters. We perform a global analysis and offer simple arguments that give essentially the same result. We also discuss determinations of solar neutrino fluxes, capabilities of future experiments, tests of CPT, implications for neutrino-less double- β decay, β decay, cosmology.

Neutrino masses and mixing: evidence and implications

Measurements of various features of the fluxes of atmospheric and solar neutrinos have provided evidence for neutrino oscillations and therefore for neutrino masses and mixing. We review the phenomenology of neutrino oscillations in vacuum and in matter. We present the existing evidence from solar and atmospheric neutrinos as well as the results from laboratory searches, including the final status of the LSND experiment. We describe the theoretical inputs that are used to interpret the experimental results in terms of neutrino oscillations. We derive the allowed ranges for the mass and mixing parameters in three frameworks: First, each set of observations is analyzed separately in a two-neutrino framework; Second, the data from solar and atmospheric neutrinos are analyzed in a three active neutrino framework; Third, the LSND results are added, and the status of accommodating all three signals in the framework of three active and one sterile light neutrinos is presented. We review the theoretical implications of these results: the existence of new physics, the estimate of the scale of this new physics and the lessons for grand unified theories, for supersymmetric models with R-parity violation, for models of extra dimensions and singlet fermions in the bulk, and for flavor models.

Nonstandard neutrino properties and the high-energy cosmic neutrino flux

Recently, it has been shown that cosmic neutrino flux at the GRB/AGN source, $F_{\nu_e}^0 : F_{\nu_{\mu}}^0 : F_{\nu_{\tau}}^0 \simeq 1 :2 :0 $, inevitably oscillates (in the three neutrino framework) to 1 : 1: 1, irrespective of the mixing angle relevant to the solar data. It has also been pointed out that the intrinsic flux of the cosmic high-energy neutrinos may not have the standard ratio, in which case the cosmic neutrino flux in the far distance should be dependent of the mixing angle. For neutrinos with nonzero electromagnetic properties, we show in the latter case that matter effects on oscillations of high-energy cosmic neutrinos can substantially modify the vacuum oscillation probability, if the mass-squared difference is $\lsim 10^{-10}$ eV^2.

Analysis of atmospheric neutrino oscillations in three-flavor neutrinos

We analyze the atmospheric neutrino experiments of Super-Kamiokande (830--920 live days) using the three-flavor neutrino framework with the mass hierarchy ${m}_{1}\ensuremath{\approx}{m}_{2}\ensuremath{\ll}{m}_{3}.$ We study the sub-GeV, multi-GeV neutrinos and upward through-going and stopping muons zenith angle distributions taking into account the Earth matter effects thoroughly. We obtain the allowed regions of mass and mixing parameters $\ensuremath{\Delta}{m}_{23}^{2},$ ${\ensuremath{\theta}}_{13},$ and ${\ensuremath{\theta}}_{23}.$ In our present analysis, we used the solar neutrino small angle solution and large angle solution for $\ensuremath{\Delta}{m}_{12}^{2}$ and ${\ensuremath{\theta}}_{12}.$ $\ensuremath{\Delta}{m}_{23}^{2}$ is restricted to $0.002--0.01 {\mathrm{eV}}^{2}$ and ${\ensuremath{\theta}}_{13}&lt;13\ifmmode^\circ\else\textdegree\fi{},$ $35\ifmmode^\circ\else\textdegree\fi{}&lt;{\ensuremath{\theta}}_{23}&lt;55\ifmmode^\circ\else\textdegree\fi{}$ in 95% C.L. For ${\ensuremath{\theta}}_{12},$ there is no difference between the large angle solution and the small one. From the ${\ensuremath{\chi}}^{2}$ fit, the minimum ${\ensuremath{\chi}}^{2}=66$ (54 DOF) is obtained at $\ensuremath{\Delta}{m}_{23}^{2}=5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3} {\mathrm{eV}}^{2},$ ${\ensuremath{\theta}}_{13}=10\ifmmode^\circ\else\textdegree\fi{},$ and ${\ensuremath{\theta}}_{23}=50\ifmmode^\circ\else\textdegree\fi{}.$ In a two flavor mixing approximation $({\ensuremath{\theta}}_{13}=0),$ the minimum ${\ensuremath{\chi}}^{2}=80$ (54 DOF) is obtained at $\ensuremath{\Delta}{m}_{23}^{2}=3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3} {\mathrm{eV}}^{2}$ and ${\ensuremath{\theta}}_{23}=45\ifmmode^\circ\else\textdegree\fi{}.$ If ${\ensuremath{\theta}}_{13}=10\ifmmode^\circ\else\textdegree\fi{}$ is real, the detected ${\ensuremath{\nu}}_{e}$ events in the K2K experiment will be about 10 times as large as events expected in the ${\ensuremath{\theta}}_{13}=0$ case.

Experimental implications of leptonic CP-violation

We discuss the implications of a leptonic CP-violation in neutrino oscillation experiments and the prospects of observing it at a neutrino factory in the context of the standard three neutrino framework. If the large mixing angle MSW effect turned out to account for the solar neutrino deficit, we show that observing an asymmetry between the ν e→ν μ and ν ̄ e → ν ̄ μ oscillation probabilities would represent an exciting experimental challenge. We determine the portion of the parameter space where an evidence could be found as a function of the intensity of the muon source and of the detector size and efficiency for two different baselines. We address the problems associated with asymmetries induced by the experimental apparatus and by matter effects. Finally, we emphasize that measuring the oscillation probabilities in both the two CP-conjugated channels would help to determine θ 13 precisely.