Search

The muon decay-at-rest ($\mu$-DAR) facility provides us with an ideal platform to probe purely muonic charged-current nonstandard neutrino interactions (NSIs). We propose to probe this class of NSI effects using antineutrinos from a $\mu$-DAR source in conjunction with neutrinos from the future Tokai to Kamioka superbeam experiment with megaton Hyper Kamiokande detector (T2HK). Even though muonic NSIs are absent in neutrino production at T2HK, we show that our proposed hybrid setup comprising $\mu$-DAR and T2HK helps in alleviating the parameter degeneracies that can arise in data. Analytic considerations reveal that the oscillation probability is most sensitive to the NSI parameter in the $\mu$-e sector. For this parameter, we show that the $\mu$-DAR setup can improve on the existing bounds down to around 0.01, especially when the data are combined with neutrino data from T2HK experiment due to the lifting of parameter degeneracies. The high precision with which $\mu$-DAR can measure $\delta_{\rm{CP}}$ is shown to be robust even in the presence of the considered NSIs. Finally, we show that the combination of $\mu$-DAR along with T2HK can also be used to put mild constraints on the NSI phase in the vicinity of the maximal CP-violating value for the chosen benchmark value of $\varepsilon^{\mu e}_{\mu e}=0.01$., Comment: Matches version published in Phys. Rev. D

Recent $\nu_e$ appearance data from the Mini Booster Neutrino Experiment (MiniBooNE) are in support of the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND), which provides an indirect hint for the existence of eV-scale sterile neutrino. As these sterile neutrinos can mix with the standard active neutrinos, in this paper we explore the effect of such active-sterile mixing on the determination of various oscillation parameters by the currently running long-baseline neutrino experiments T2K and NO$\nu$A. We find that the existence of sterile neutrino can lead to new kind of degeneracies among these parameters which would substantially deteriorate the mass hierarchy sensitivity of NO$\nu$A experiment. We further notice that the inclusion of data from T2K experiment helps in resolving the degeneracies. The impact of new CP violating phases $\delta_{14}$ and $\delta_{34}$ on the maximal CP-violation exclusion sensitivity for NO$\nu$A experiment has also been illustrated. Finally, we discuss the implication of such light sterile neutrinos on neutrinoless double beta decay processes in line with recent experimental results, as well as on the sensitivity reach of future experiments., Comment: 22 pages, 8 figures, published version

Neutrinos are the fundamental particles, blind to all kind of interactions except the weak and gravitational. Hence, they can propagate very long distances without any deviation. This characteristic property can thus provide an ideal platform to investigate Planck suppressed physics through their long distance propagation. In this work, we intend to investigate CPT violation through Lorentz invariance violation (LIV) in the long-baseline accelerator based neutrino experiments. Considering the simplest four-dimensional Lorentz violating parameters, for the first time, we obtain the sensitivity limits on the LIV parameters from the currently running long-baseline experiments T2K and NO$\nu$A. In addition to this, we show their effects on mass hierarchy and CP violation sensitivities by considering NO$\nu$A as a case study. We find that the sensitivity limits on LIV parameters obtained from T2K are much weaker than that of NO$\nu$A and the synergy of T2K and NO$\nu$A can improve these sensitivities. All these limits are slightly weaker ($2 \sigma$ level) compared to the values extracted from Super-Kamiokande experiment with atmospheric neutrinos. Moreover, we observe that the mass hierarchy and CPV sensitivities are either enhanced or deteriorated significantly in the presence of LIV as these sensitivities crucially depend on the new CP-violating phases. We also present the correlation between $\sin^2 \theta_{23}$ and the LIV parameter $|a_{\alpha \beta}|$, as well as $\delta_{CP}$ and $|a_{\alpha \beta}|$., Comment: 27 pages, 10 figures, version to appear in EPJC

Recent $\nu_e$ appearance data from the Mini Booster Neutrino Experiment (MiniBooNE) are in support of the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND), which provides an indirect hint for the existence of eV-scale sterile neutrino. As these sterile neutrinos can mix with the standard active neutrinos, in this paper we explore the effect of such active-sterile mixing on the determination of various oscillation parameters by the currently running long-baseline neutrino experiments T2K and NO$\nu$A. We find that the existence of sterile neutrino can lead to new kind of degeneracies among these parameters which would substantially deteriorate the mass hierarchy sensitivity of NO$\nu$A experiment. We further notice that the inclusion of data from T2K experiment helps in resolving the degeneracies. The impact of new CP violating phases $\delta_{14}$ and $\delta_{34}$ on the maximal CP-violation exclusion sensitivity for NO$\nu$A experiment has also been illustrated. Finally, we discuss the implication of such light sterile neutrinos on neutrinoless double beta decay processes in line with recent experimental results, as well as on the sensitivity reach of future experiments., Comment: 22 pages, 8 figures, published version

The muon decay-at-rest ($\mu$-DAR) facility provides us with an ideal platform to probe purely muonic charged-current nonstandard neutrino interactions (NSIs). We propose to probe this class of NSI effects using antineutrinos from a $\mu$-DAR source in conjunction with neutrinos from the future Tokai to Kamioka superbeam experiment with megaton Hyper Kamiokande detector (T2HK). Even though muonic NSIs are absent in neutrino production at T2HK, we show that our proposed hybrid setup comprising $\mu$-DAR and T2HK helps in alleviating the parameter degeneracies that can arise in data. Analytic considerations reveal that the oscillation probability is most sensitive to the NSI parameter in the $\mu$-e sector. For this parameter, we show that the $\mu$-DAR setup can improve on the existing bounds down to around 0.01, especially when the data are combined with neutrino data from T2HK experiment due to the lifting of parameter degeneracies. The high precision with which $\mu$-DAR can measure $\delta_{\rm{CP}}$ is shown to be robust even in the presence of the considered NSIs. Finally, we show that the combination of $\mu$-DAR along with T2HK can also be used to put mild constraints on the NSI phase in the vicinity of the maximal CP-violating value for the chosen benchmark value of $\varepsilon^{\mu e}_{\mu e}=0.01$., Comment: Matches version published in Phys. Rev. D

Neutrinos are the fundamental particles, blind to all kind of interactions except the weak and gravitational. Hence, they can propagate very long distances without any deviation. This characteristic property can thus provide an ideal platform to investigate Planck suppressed physics through their long distance propagation. In this work, we intend to investigate CPT violation through Lorentz invariance violation (LIV) in the long-baseline accelerator based neutrino experiments. Considering the simplest four-dimensional Lorentz violating parameters, for the first time, we obtain the sensitivity limits on the LIV parameters from the currently running long-baseline experiments T2K and NO$\nu$A. In addition to this, we show their effects on mass hierarchy and CP violation sensitivities by considering NO$\nu$A as a case study. We find that the sensitivity limits on LIV parameters obtained from T2K are much weaker than that of NO$\nu$A and the synergy of T2K and NO$\nu$A can improve these sensitivities. All these limits are slightly weaker ($2 \sigma$ level) compared to the values extracted from Super-Kamiokande experiment with atmospheric neutrinos. Moreover, we observe that the mass hierarchy and CPV sensitivities are either enhanced or deteriorated significantly in the presence of LIV as these sensitivities crucially depend on the new CP-violating phases. We also present the correlation between $\sin^2 \theta_{23}$ and the LIV parameter $|a_{\alpha \beta}|$, as well as $\delta_{CP}$ and $|a_{\alpha \beta}|$., Comment: 27 pages, 10 figures, version to appear in EPJC

In this paper, we consider the low-energy scale inverse seesaw mechanism in which the observed neutrino mass and lepton mixing are explained by introducing right handed neutrinos and the gauge-singlet fermions with experimentally testable energy scale. Moreover, the presence of such new fermions leads to unitarity violation in lepton mixing due to significantly large mixing between active neutrinos and the heavy fermions. In addition to this, such large lepton mixing also gives rise to potentially large lepton flavor violation, which allows to constrain the non-unitarity parameters via lepton flavor violating decays ($l_i \to l_j \gamma$). We make use of these constraints on non-unitarity parameters and investigate their effects on the determination of current unknown oscillation parameters at long-baseline experiments. We find that non-unitarity parameters are sensitive to NO$\nu$A experiment. However, it is observed that NO$\nu$A experiment is not expected to improve the current knowledge of non-unitarity parameter $\eta_{21}$. We also find that the sensitivities to current unknowns are deteriorated significantly in presence of non-unitary lepton mixing and these sensitivities crucially depend upon the new CP-violating phase in the non-unitary mixing. Further, we find that the degeneracy resolution capability of NO$\nu$A experiment is reduced in the presence of non-unitarity parameters. However, the synergy between the currently running experiments T2K and NO$\nu$A can improve the parameter degeneracy resolution and hence there is enhancement in the sensitivities of unknowns., Comment: 29 pages, 14 figures, typos corrected, included analysis on degeneracy resolution

The observation of neutrino oscillation as well as the recent experimental result on lepton flavor universality (LFU) violation in $B$ meson decays are indications of new physics beyond the Standard Model. Many theoretical models, which are introduced in the literature as an extension of SM to explain these observed deviations in LFU, lead to new kind of interactions so-called non-standard interaction (NSI) between the elementary particles. In this paper, we consider a model with an additional $Z'$ boson (which is quite successful in explaining the observed LFU anomalies) and analyze its effect in the lepton flavour violating (LFV) $B_d\to \tau^\pm e^\mp$ decay modes. From the present upper bound of the $B_d\to \tau^\pm e^\mp$ branching ratio, we obtain the constraints on the new physics parameters, which are related to the corresponding NSI parameters in the neutrino sector by $SU(2)_L$ symmetry. These new parameters are expected to have potential implications in the neutrino oscillation studies and in this work we investigate the possibility of observing the effects of these interactions in the currently running and upcoming long-baseline experiments, i.e., NOvA and DUNE respectively., Comment: 20 pages, 7 figures, to appear in EPJC. arXiv admin note: substantial text overlap with arXiv:1603.02184

In this paper, we consider the low-energy scale inverse seesaw mechanism in which the observed neutrino mass and lepton mixing are explained by introducing right handed neutrinos and the gauge-singlet fermions with experimentally testable energy scale. Moreover, the presence of such new fermions leads to unitarity violation in lepton mixing due to significantly large mixing between active neutrinos and the heavy fermions. In addition to this, such large lepton mixing also gives rise to potentially large lepton flavor violation, which allows to constrain the non-unitarity parameters via lepton flavor violating decays ($l_i \to l_j \gamma$). We make use of these constraints on non-unitarity parameters and investigate their effects on the determination of current unknown oscillation parameters at long-baseline experiments. We find that non-unitarity parameters are sensitive to NO$\nu$A experiment. However, it is observed that NO$\nu$A experiment is not expected to improve the current knowledge of non-unitarity parameter $\eta_{21}$. We also find that the sensitivities to current unknowns are deteriorated significantly in presence of non-unitary lepton mixing and these sensitivities crucially depend upon the new CP-violating phase in the non-unitary mixing. Further, we find that the degeneracy resolution capability of NO$\nu$A experiment is reduced in the presence of non-unitarity parameters. However, the synergy between the currently running experiments T2K and NO$\nu$A can improve the parameter degeneracy resolution and hence there is enhancement in the sensitivities of unknowns., Comment: 29 pages, 14 figures, typos corrected, included analysis on degeneracy resolution

The observation of neutrino oscillation as well as the recent experimental result on lepton flavor universality (LFU) violation in $B$ meson decays are indications of new physics beyond the Standard Model. Many theoretical models, which are introduced in the literature as an extension of SM to explain these observed deviations in LFU, lead to new kind of interactions so-called non-standard interaction (NSI) between the elementary particles. In this paper, we consider a model with an additional $Z'$ boson (which is quite successful in explaining the observed LFU anomalies) and analyze its effect in the lepton flavour violating (LFV) $B_d\to \tau^\pm e^\mp$ decay modes. From the present upper bound of the $B_d\to \tau^\pm e^\mp$ branching ratio, we obtain the constraints on the new physics parameters, which are related to the corresponding NSI parameters in the neutrino sector by $SU(2)_L$ symmetry. These new parameters are expected to have potential implications in the neutrino oscillation studies and in this work we investigate the possibility of observing the effects of these interactions in the currently running and upcoming long-baseline experiments, i.e., NOvA and DUNE respectively., Comment: 20 pages, 7 figures, to appear in EPJC. arXiv admin note: substantial text overlap with arXiv:1603.02184

Recently, the reactor mixing angle $\theta_{13}$ has been measured precisely by Daya Bay, RENO and T2K experiments with a moderately large value. However, the standard form of neutrino mixing patterns such as bimaximal, tri-bimaximal, golden ratio of types A and B, hexagonal etc., which are based on certain flavor symmetries, predict vanishing $\theta_{13}$. Using the fact that the neutrino mixing matrix can be represented as $V_{\rm PMNS}=U_l^{\dagger} U_\nu P_\nu$, where $U_l$ and $U_\nu$ result from the diagonalization of the charged lepton and neutrino mass matrices and $P_\nu$ is a diagonal matrix containing Majorana phases, we explore the possibility of accounting for the large reactor mixing angle by considering deviations both in the charged lepton and neutrino sector. In the charged lepton sector we consider the deviation as an additional rotation in the (12) and (13) planes, whereas in neutrino sector we consider deviations to various neutrino mixing patterns through (13) and (23) rotations. We find that with the inclusion of these deviations it is possible to accommodate the observed large reactor mixing angle $\theta_{13}$, and one can also obtain limits on the CP violating Dirac phase $\delta_{CP}$ and Jarlskog invariant $J_{CP}$ for most of the cases. We then explore whether our findings can be tested in the currently running NO$\nu$A experiment with 3 years of data taking in neutrino mode followed by 3 years with anti-neutrino mode., Comment: 23 pages, 5 figures, revised version, to appear in New Journal of Physics

Recently, the reactor mixing angle $\theta_{13}$ has been measured precisely by Daya Bay, RENO and T2K experiments with a moderately large value. However, the standard form of neutrino mixing patterns such as bimaximal, tri-bimaximal, golden ratio of types A and B, hexagonal etc., which are based on certain flavor symmetries, predict vanishing $\theta_{13}$. Using the fact that the neutrino mixing matrix can be represented as $V_{\rm PMNS}=U_l^{\dagger} U_\nu P_\nu$, where $U_l$ and $U_\nu$ result from the diagonalization of the charged lepton and neutrino mass matrices and $P_\nu$ is a diagonal matrix containing Majorana phases, we explore the possibility of accounting for the large reactor mixing angle by considering deviations both in the charged lepton and neutrino sector. In the charged lepton sector we consider the deviation as an additional rotation in the (12) and (13) planes, whereas in neutrino sector we consider deviations to various neutrino mixing patterns through (13) and (23) rotations. We find that with the inclusion of these deviations it is possible to accommodate the observed large reactor mixing angle $\theta_{13}$, and one can also obtain limits on the CP violating Dirac phase $\delta_{CP}$ and Jarlskog invariant $J_{CP}$ for most of the cases. We then explore whether our findings can be tested in the currently running NO$\nu$A experiment with 3 years of data taking in neutrino mode followed by 3 years with anti-neutrino mode., Comment: 23 pages, 5 figures, revised version, to appear in New Journal of Physics