Elastic scattering of transversely polarized electron antineutrino beam off unpolarized electrons can be used to detect the CP-violating effects by measuring the azimuthal asymmetry of recoil electrons caused by the interference terms between the standard vector $c_{V}^{L}$, axial $c_{A}^{L}$ couplings of left-chirality antineutrinos and exotic scalar $c_{S}^{R}$ coupling of right-chirality ones in the differential cross section. It would be a positive evidence for the existence of the exotic antineutrino states. Moreover, we also show that the differential cross section for the $\overlineν e^- $ scattering can be obtained from the one for the $νe$ scattering, if one makes the substitution $c_{T}^{R} \to -c_{T}^{R}$, $c_{A}^{L} \to -c_{A}^{L}$, ${\bf q}\to -{\bf q}$, ${\boldmath $\hatη_ν$}\to -{\boldmath $\hatη_ν$}$.
Tests of Lorentz and CPT violation in the medium baseline reactor antineutrino experiment are presented in the framework of the Standard Model Extension (SME). Both the spectral distortion and sidereal variation are employed to derive the limits of Lorentz violation (LV) coefficients. We do the numerical analysis of the sensitivity of LV coefficients by taking the Jiangmen Underground Neutrino Observatory (JUNO) as an illustration, which can improve the sensitivity by more than two orders of magnitude compared with the current limits from reactor antineutrino experiments.
The effects of perturbative Lorentz and CPT violation on neutrino oscillations are studied. Features include neutrino-antineutrino oscillations, direction dependence, and unconventional energy behavior. Leading-order corrections arising from renormalizable operators are derived in the general three-flavor effective field theory. The results are applied to neutrino-beam experiments with long baselines, which offer excellent sensitivity to the accompanying effects. Key signatures of Lorentz and CPT violation using neutrino beams include sidereal variations in the oscillation probabilities arisin…
If massive neutrinos are Majorana particles, then the lepton number should be violated and neutrino-antineutrino oscillations will take place. In this talk, we present the properties of CP violation in neutrino-antineutrino oscillations with a non-unitary leptonic flavor mixing matrix, which naturally arises in the type-I seesaw model due to the mixing between light and heavy Majorana neutrinos. Taking into account current experimental bounds on the leptonic unitarity violation, we show that the CP asymmetries induced by the non-unitary mixing parameters can significantly deviate from those in…
Discussing the recent MINOS data on muon anti-neutrino disappearance and the MiniBooNE data on muon anti-neutrino to electron anti-neutrino oscillation, we show that the while the respective best fits are inconsistent with each other, significant overlap of allowed regions does exist. Assuming only three neutrino species, the data indicates a discrepancy of mass levels and mixing angles between the neutrino and the antineutrino sectors. We show that the existing data can be reconciled with a model of explicit CPT violation in the neutrino sector and estimate the magnitude of the required viola…
Elastic scattering of neutrinos and antineutrinos on nucleons is considered. It is shown that the measurement of the neutrino-antineutrino asymmetry would allow to obtain model independent informations on the strange axial and vector form factors. The ratio of the magnetic form factors of the proton and neutron, on which the asymmetry depends, is investigated in detail. The asymmetry is calculated under different assumptions on the behavior of the strange vector and axial form factors.
If massive neutrinos are Majorana particles, then the lepton number should be violated in nature and neutrino-antineutrino oscillations $ν^{}_α\leftrightarrow \overlineν^{}_β$ (for $α, β= e, μ, τ$) will definitely take place. In the present paper, we study the properties of CP violation in neutrino-antineutrino oscillations with the non-unitary leptonic flavor mixing matrix, which is actually a natural prediction in the canonical seesaw model due to the mixing between light and heavy Majorana neutrinos. The oscillation probabilities $P(ν^{}_α\to \overlineν^{}_β)$ and $P(\overlineν^{}_α\to ν^{}…
We investigate the recently suggested scheme of independent mass matrices for neutrinos and antineutrinos. Such a CPT violating scheme is able to account for all neutrino data with the three known flavors. For atmospheric neutrinos this means that it is possible to have different mass squared differences driving the oscillation for neutrinos and antineutrinos. We analyze the atmospheric and K2K data within the simplest scheme of two neutrino oscillation, neglecting electron neutrino oscillation. We find that the preferred region is close to the CPT conserving mass spectra. However the spectra …
If finite but tiny masses of the three active neutrinos are generated via the canonical seesaw mechanism with three heavy sterile neutrinos, the 3\times 3 Pontecorvo-Maki-Nakagawa-Sakata neutrino mixing matrix V will not be exactly unitary. This kind of indirect unitarity violation can be probed in a precision reactor antineutrino oscillation experiment, but it may be entangled with terrestrial matter effects as both of them are very small. We calculate the probability of \overlineν_e \to \overlineν_e oscillations in a good analytical approximation, and find that, besides the zero-distance eff…
We analyzed the electron neutrino data of the Gallium radioactive source experiments and the electron antineutrino data of the reactor Bugey and Chooz experiments in terms of neutrino oscillations allowing for a CPT-violating difference of the squared-masses and mixings of neutrinos and antineutrinos. We found that the discrepancy between the disappearance of electron neutrinos indicated by the data of the Gallium radioactive source experiments and the limits on the disappearance of electron antineutrinos given by the data of reactor experiments reveal a positive CPT-violating asymmetry of the…
The next generation of long baseline neutrino oscillation experiments will aim at determining the unknown mixing angle $θ_{13}$, the type of neutrino mass hierarchy and CP-violation. We discuss the separation of these properties by means of the energy dependence of the oscillation probability and we consider an hybrid setup which combines the electron capture and the $β^+$ decay from the same radioactive ion with the same boost. We study the sensitivity to the mixing angle and the CP-phase, the CP discovery potential and the reach to determine the type of neutrino mass hierarchy. The analysis …
We searched for a sidereal modulation in the rate of neutrinos observed by the MINOS far detector. The detection of these signals could be a signature of neutrino-antineutrino mixing due to Lorentz and CPT violation as described by the Standard-Model Extension framework. We found no evidence for these sidereal signals and we placed limits on the coefficients in this theory describing the effect.
The long-baseline experiment T2K in Japan has collected data in the neutrino mode corresponding to an exposure of $6.57 \times 10^{20}$ POT (Protons on Target) and currently it is running in the antineutrino mode. The main aim of the antineutrino run is to measure the leptonic phase $δ_{CP}$ which may help to understand the matter-antimatter asymmetry of the universe. In this work we show that in T2K, antineutrinos are required only for removing the wrong octant solutions which in turn improves the CP sensitivity. If however the octant is known then pure neutrino run is capable of giving the m…
The main aim of the T2K experiment in Japan is to discover CP violation in the leptonic sector by measuring the Dirac phase $δ_{CP}$. For that purpose T2K has already started collecting data in both neutrino and antineutrino mode. But in this work we will show that, in T2K the main role of the antineutrinos is to resolve the octant degeneracy. If the octant is known then the pure neutrino run of T2K is capable to give the maximum CP sensitivity. On the other hand in the experiment like NO$ν$A, antineutrinos are still useful even when octant is known. Thus we propose that let T2K run in the dom…
The effect of the second class currents with and without time reversal invariance has been studied in the quasielastic production of nucleons and hyperons induced by neutrinos and antineutrinos from the nucleons. The numerical results are presented for the total scattering cross section~($σ$) as well as for the longitudinal, perpendicular and transverse components of the polarization of the final baryons ($p$, $n$, $Λ$, $Σ^-$, $Σ^0$) and muon produced in the quasielastic (anti)neutrino-nucleon scattering induced by the weak charged current. In the case of the production of $Λ$ hyperon, which i…
Violations of CPT invariance can induce neutrino-to-antineutrino transitions. We study this effect for solar neutrinos and use the upper bound on the solar neutrino-to-antineutrino transition probability from the KamLAND experiment to constrain CPT-symmetry-violating coefficients of the general Standard-Model Extension. The long propagation distance from the Sun to the Earth allows us to improve existing limits by factors ranging from about a thousand to $10^{11}$.
We discuss the nuclear interactions of neutrinos versus those of antineutrinos, a relevant comparison for CP violation experiments in the neutrino sector. We consider the MiniBooNE quasielastic-like double differential neutrinos and antineutrinos cross sections which are flux dependent and hence specific to the MiniBooNE set-up. We combine them introducing their sum and their difference. We show that the last combination can bring a general information, which can be exploited in other experiments, on the nuclear matrix elements of the axial vector interference term. Our theoretical model repro…
Neutrino-antineutrino conversion is an important new physics process. The observation of this phenomenon could indicate total lepton number violation and potential CPT-violation. Searching for the appearance of electron antineutrinos from solar neutrinos from $\rm^8B$ decay allows us to hunt for this rare process, although it can also be explained by other mechanisms or hypotheses. This analysis examines the capabilities of observing neutrino-antineutrino transition from $\rm^8B$ unoscillated solar neutrinos using different liquid scintillator detector configurations. High energy reactor neutr…
If the massive neutrinos are the Majorana particles, how to pin down the Majorana CP-violating phases will eventually become an unavoidable question relevant to the future neutrino experiments. We argue that a study of neutrino-antineutrino oscillations will greatly help in this regard, although the issue remains purely academic at present. In this work we first derive the probabilities and CP-violating asymmetries of neutrino-antineutrino oscillations in the three-flavor framework, and then illustrate their properties in two special cases: the normal neutrino mass hierarchy with m_1 = 0 and t…
The first hint of the leptonic CP phase $δ_{CP}=-90^\circ$ has already came from the long-baseline neutrino oscillation experiment T2K. This hint is derived from the neutrino data of T2K and currently it is running in the antineutrino mode. In this work we ask the question what should be the proportion of neutrino and antineutrino running of the T2K experiment to discover CP violation in the leptonic sector.
A recently developed Standard-Model Extension (SME) formalism for neutrino oscillations that includes Lorentz and CPT violation is used to analyze the sidereal time variation of the neutrino event excess measured by the Liquid Scintillator Neutrino Detector (LSND) experiment. The LSND experiment, performed at Los Alamos National Laboratory, observed an excess, consistent with neutrino oscillations, of ${\barν}_e$ in a beam of ${\barν}_μ$. It is determined that the LSND oscillation signal is consistent with no sidereal variation. However, there are several combinations of SME coefficients that …
We consider searching for light sterile fermions and new forces by using long baseline oscillations of neutrinos and antineutrinos. A new light sterile state and/or a new force can lead to apparent CPT violation in muon neutrino and antineutrino oscillations. As an example, we present an economical model of neutrino masses containing a sterile neutrino. The potential from the Standard Model neutral current gives rise to a difference between the disappearance probabilities of neutrinos and antineutrinos, when mixing with a light sterile neutrino is considered. The addition of a B-L interaction …
We hunt for and discuss manifestly CP-violating effects which are mediated by Majorana phases. These phases are present if the Standard Model neutrinos are Majorana particles. We argue that while Majorana phases do affect the strength of neutrinoless double beta decay (a well known fact), they do so in a way that involves no manifest violation of CP. The conditions for manifestly CP-violating phenomena -- differences between the rates for CP-mirror-image processes -- are presented, and three examples are discussed: (i) neutrino-antineutrino oscillation; (ii) rare decays of K and B mesons and t…
A recent work [Y. Huang and B.-Q. Ma, Commun. Phys. {\bf 1}, 62 (2018)] associated all four PeV neutrinos observed by IceCube to gamma-ray bursts (GRBs), and revealed a regularity which indicates a Lorentz violation scale $E_{\rm LV}=(6.5\pm0.4)\times10^{17}$ GeV with opposite sign factors $s=\pm 1$ between neutrinos and antineutrinos. The association of "time delay" and "time advance" events with neutrinos and antineutrinos (or vice versa) is only a hypothesis since the IceCube detector cannot tell the chirality of the neutrinos, and further experimental tests are needed to verify this hypoth…
We consider elastic antineutrino-electron scattering taking into account possible effects of neutrino masses and mixing and of neutrino magnetic moments and electric dipole moments. Having in mind antineutrinos produced in a nuclear reactor we compute, in particular, the weak-electromagnetic interference terms which are linear in the magnetic (electric dipole) moments and also in the neutrino masses. We show that these terms are, however, suppressed compared to the pure weak and electromagnetic cross section. We also comment upon the possibility of using the electromagnetic cross section to in…
The Double Chooz reactor-based oscillation experiment searches for an electron antineutrino disappearance signal to investigate the neutrino mass matrix mixing angle theta 13. Double Chooz's reported evidence for this disappearance is generally interpreted as mass-driven mixing through this parameter. However, the electron antineutrino candidates collected by the experiment can also be used to search for a signature of the violation of Lorentz invariance. We study the sidereal time dependence of the antineutrino signal rate and probe Lorentz violation within the Standard-Model Extension (SME) …
We discuss a possibility that the so-called reactor antineutrino anomaly can be, at least in part, explained by applying a quantum field-theoretical approach to neutrino oscillations, which in particular predicts a small deviation from the classical inverse-square law at short but macroscopic distances between the neutrino source and detector. An extensive statistical analysis of the reactor data is performed to examine this speculation.
According to different effects on neutrino oscillations, the unitarity violation in the MNSP matrix can be classified into the direct unitarity violation and the indirect unitarity violation which are induced by the existence of the light and the heavy sterile neutrinos respectively. Of which sub-eV sterile neutrinos are of most interesting. We study in this paper the possibility of searching for sub-eV sterile neutrinos in the precision reactor antineutrino oscillation experiments with three different baselines at around 500 m, 2 km and 60 km. We find that the antineutrino survival probabilit…
The 96.4 day exposure of a 3 kg ultra-low noise germanium detector to the high flux of antineutrinos from a power nuclear reactor is described. A very strong preference ($p<1.2\times10^{-3}$) for the presence of a coherent elastic neutrino-nucleus scattering (CE$ν$NS) component in the data is found, when compared to a background-only model. No such effect is visible in 25 days of operation during reactor outages. The best-fit CE$ν$NS signal is in good agreement with expectations based on a recent characterization of germanium response to sub-keV nuclear recoils. Deviations of order 60\% from t…
We develop a non-adiabatic perturbation theory for oscillations involving an arbitrary number of neutrino and antineutrino species, including the possibility of lepton number violation which we treat as a small effect. We interpret the physics of such an approach for the one generation case by introducing the notion of adiabaticity for neutrino and antineutrino oscillations in analogy to flavor oscillations. We find that in a CP-odd matter environment a small lepton number violation in vacuo can be enhanced. Eventually, we apply the perturbation theory to the two generation case and work out a…
We study the consequences of CPT and lepton number violation in neutrino sector. For CPT violation we take gravity with which neutrino and antineutrino couple differently. Gravity mixes neutrino and antineutrino in an unequal ratio to give two mass eigenstates. Lepton number violation interaction together with CPT violation gives rise to neutrino-antineutrino oscillation. Subsequently, we study the neutrino flavor mixing and oscillation under the influence of gravity. It is found that gravity changes flavor oscillation significantly which influences the relative abundance of different flavors …
Neutrino-nucleus $νA\to νA$ and antineutrino-nucleus $\barνA\to \barνA$ interactions, when the nucleus conserves its integrity, are discussed with coherent (elastic) and incoherent (inelastic) scattering regimes taken into account. In the first regime the nucleus remains in the same quantum state after the scattering and the cross-section depends on the quadratic number of nucleons. In the second regime the nucleus changes its quantum state and the cross-section has an essentially linear dependence on the number of nucleons. The coherent and incoherent cross-sections are driven by a nuclear nu…
The p-value or statistical significance of a CP conservation null hypothesis test is determined from counting electron neutrino and antineutrino appearance oscillation events. The statistical estimates include cases with background events and different data sample sizes, graphical plots to interpret results and methods to combine p-values from different experiments. These estimates are useful for optimizing the search for CP violation with different amounts of neutrino and antineutrino beam running, comparing results from different experiments and for simple cross checks of more elaborate stat…
Short distance reactor antineutrino experiments measure an antineutrino spectrum a few percent lower than expected from theoretical predictions. In this work we study the potential of low energy threshold reactor experiments in the context of a light sterile neutrino signal. We discuss the perspectives of the recently detected coherent elastic neutrino-nucleus scattering in future reactor antineutrino experiments. We find that the expectations to improve the current constraints on the mixing with sterile neutrinos are promising. We also analyse the measurements of antineutrino scattering off e…
A MINOS result seemed to hint a different anti-neutrino mass splitting and mixing angle with respect to the neutrino ones, offering a hint for a CPT violation in lepton sector. However more recent MINOS data reduced the neutrino-antineutrino differences leading to a narrow discrepancy almost compatible with no CPT violation, hard to be disentangled. Moreover last a few years of OPERA activity on tau appearance is still un-probed (one unique event). Both flavor muon-tau mixing, tau appearance and eventual CPT violation disentanglement need more tools to be enhanced. Atmospheric muon neutrino sp…
We show the existence of dynamical zeros in the helicity amplitudes for neutrino-electron elastic scattering at lowest order in the standard theory. In particular, the $λ=1/2$ non-flip electron helicity amplitude in the electron antineutrino process vanishes for an incident neutrino energy $E_ν=m_{e}/(4sin^{2}θ_{W})$ and forward electrons (maximum recoil energy). The rest of helicity amplitudes show kinematical zeros in this configuration and therefore the cross section vanishes. Prospects to search for neutrino magnetic moment are discussed.
We investigate neutrino-nucleus interactions at energies around 1 GeV. In this regime, the main contributions to the cross sections come from quasi-elastic and $Δ$ production processes. Our formalism, based on the Impulse Approximation is well suited to describe both types of interactions. We focus on a series of important nuclear effects in the interaction of electron neutrinos with $^{16}O$, also relevant to future $β$-Beams. Our results show that the Fermi gas model, widely used in data analysis of neutrino experiments, overestimates the total cross sections by as much as 20 %.
The analysis of the recent neutral-current elastic neutrino and antineutrino-nucleus scattering cross sections measured by the MiniBooNE Collaboration requires relativistic theoretical descriptions also accounting for the role of final-state interactions. In this work we investigate the sensitivity to final-state interactions and compare the MiniBooNE data with the results obtained in the relativistic Green's function model with different parameterizations for the phenomenological relativistic optical potential.
In this paper, we indicate the theoretical possibility of using the decay of polarized muons at rest as a source of the transversely polarized electron antineutrino beam. Such a beam can be used to probe new effects beyond standard model. We mean here new tests concerning CP violation, Lorentz structure and chirality structure of the charged current weak interactions. The main goal is to show how the energy and angular distribution of the electron antineutrinos in the muon rest frame depends on the transverse components of the antineutrino beam polarization. Our analysis is model-independent a…
The quasielastic weak production of $Λ$ and $Σ$ hyperons from nucleons and nuclei induced by antineutrinos is studied in the energy region of some ongoing neutrino oscillation experiments in the intermediate energy region. The hyperon nucleon transition form factors determined from neutrino nucleon scattering and an analysis of high precision data on semileptonic decays of neutron and hyperons using SU(3) symmetry have been used. The nuclear effects due to Fermi motion and final state interaction effects due to hyperon nucleon scattering have also been studied. The numerical results for differ…
We study both the elastic ($νe \rightarrow νe$) and the radiative process ($νe \rightarrow νe γ$) and discuss how these processes can shed light on some current topics in neutrino physics such as a neutrino magnetic moment and neutrino oscillations. The radiative process allows to reach low values of $Q^2$ without the need to operate at very small energies of recoil electrons, a favourable scenario to search for a neutrino magnetic moment. The elastic cross section contains a dynamical zero at $E_ν=m/(4 sin^2θ_{W})$ and forward electrons for the electron antineutrino channel, which is reachabl…
The Standard Model differential cross section for $\barν_e-e^-$ elastic scattering vanishes exactly, at lowest order, for forward electrons and incident $\barν_e$ energy close to the rest energy of the electron. This dynamical zero is not induced by a fundamental symmetry of the Lagrangian but by a destructive interference between the left- and right-handed chiral couplings of the electron in the charged and neutral current amplitudes. We show that lowest order analyses based on this favorable kinematic configuration are only mildly affected by the inclusion of the $O(α)$ radiative corrections…
Recent experimental results and developments in the theoretical treatment of neutrino-nucleus interactions in the energy range of 1-10 GeV are discussed. Difficulties in extracting neutrino-nucleon cross sections from neutrino-nucleus scattering data are explained and significance of understanding nuclear effects for neutrino oscillation experiments is stressed. Detailed discussions of the status of two-body current contribution in the kinematic region dominated by quasi-elastic scattering and specific features of partonic nuclear effects in weak DIS scattering are presented.
Starting from a short range expansion of the inelastic overlap function, capable of describing quite well the elastic pp and $\bar{p}p$ scattering data, we obtain extensions to the inelastic channel, through unitarity and an impact parameter approach. Based on geometrical arguments we infer some characteristics of the elementary hadronic process and this allows an excellent description of the inclusive multiplicity distributions in $pp$ and $\bar{p}p$ collisions. With this approach we quantitatively correlate the violations of both geometrical and KNO scaling in an analytical way. The physical…
Data from the MINOS experiment has been used to search for mixing between muon neutrinos and muon antineutrinos using a time-independent Lorentz-violating formalism derived from the Standard-Model Extension (SME). MINOS is uniquely capable of searching for muon neutrino-antineutrino mixing given its long baseline and ability to distinguish between neutrinos and antineutrinos on an event-by-event basis. Neutrino and antineutrino interactions were observed in the MINOS Near and Far Detectors from an exposure of 10.56$\times10^{20}$ protons-on-target from the NuMI neutrino-optimized beam. No evid…
We calculate the total and differential quasielastic cross sections for neutrino and antineutrino scattering on nucleons using up to date fits to the nucleon elastic electromagnetic form factors $G_E^p$, $G_E^n$, $G_M^p$, $G_M^n$, and weak and pseudoscalar form factors. We find that using the updated non-zero value of $G_E^n$ has a significant effect on both the total and differential neutrino and antineutrino quasielastic cross sections. Previous extractions of the weak axial form factor from neutrino scattering data are sensitive to the assumptions that were used for the vector form factors.…
We study the elastic scattering of the lightest neutralino with a nucleus in the framework of the minimal supersymmetric standard model (MSSM) with explicit flavor preserving CP violation, including the one-loop CP-violating neutral Higgs-boson mixing effects induced dominantly by the CP phases in the top and bottom (s)quark sectors. We construct the most general form of the effective Lagrangian for the neutralino-nucleus scattering in the limit of vanishing momentum transfers and then we perform a comprehensive analysis of the effects of the complex CP phases on the mass spectra of the lighte…
In this paper we consider a Beta Beam setup that tries to leverage at most existing European facilities: i.e. a setup that takes advantage of facilities at CERN to boost high-Q ions (8Li and 8B) aiming at a far detector located at L = 732 Km in the Gran Sasso Underground Laboratory. The average neutrino energy for 8Li and 8B ions boosted at γ~ 100 is in the range E_ν= [1,2] GeV, high enough to use a large iron detector of the MINOS type at the far site. We perform, then, a study of the neutrino and antineutrino fluxes needed to measure a CP-violating phase delta in a significant part of the pa…
In the last years the Lorentz Violation scheme was implemented in QFT, in special in standard model of particle physics, in an attempt to explain our actual open problems. In this work we analyze nonminimal couplings between a Lorentz-violating 4-vector and the photon field and the leptonic current of QED. The 1-loop contribution of the elastic photon-photon scattering is showed and the novel characteristics which arose are pointed out.
New measurements of the coherent elastic neutrino-nucleus scattering (CEvNS) are expected to be achieved in the near future by using two neutrino production channels with different energy distributions: the very low energy electron antineutrinos from reactor sources and the muon and electron neutrinos from spallation neutron sources (SNS) with a relatively higher energy. Although precise measurements of this reaction would allow an improved knowledge of standard and beyond the Standard Model physics, it is important to distinguish the different new contributions to the process. We illustrate t…
Previous studies on high-energy gamma-ray burst neutrinos from IceCube suggest a neutrino speed variation at the Lorentz violation~(LV) scale of $\sim 6.4\times 10^{17}$~GeV, with opposite velocity variances between neutrinos and antineutrinos. Within a space-time foam model, inspired by string theory, we develop an approach to describe the suggested neutrino/antineutrino propagation properties with both Lorentz invariance and CPT symmetry breaking. A threshold analysis on the bremsstrahlung of electron-positron pair~($ν\rightarrowνee^{+}$) for the superluminal~(anti)neutrino is performed. We …
