Search

Dark photons coupling to $L_\mu-L_\tau$ lepton number difference are a highly studied light dark matter candidate, with potential to be discovered through their impact on terrestrial neutrino oscillation experiments. We re-examine this in the light of claimed tensions between the NO$\nu$A and T2K long baseline experiments, also taking into account data from the MINOS experiment. We obtain leading limits on the $L_\mu-L_\tau$ gauge coupling $g'$ versus dark photon mass $m_{A'}$, and find no statistically significant alleviation of the tension from inclusion of the new physics effect., Comment: 5 pages, 1 figure

In this article, we review the status of the tension between the long-baseline accelerator neutrino experiments T2K and NO$\nu$A. The tension arises mostly due to the mismatch in the appearance data of the two experiments. We explain how this tension arises based on $\nu_\mu \to \nu_e$ and $\bar{\nu}_\mu \to \bar{\nu}_e$ oscillation probabilities. We define the reference point of vacuum oscillation, maximal $\theta_{23}$ and $\delta_{CP}=0$ and compute the $\nu_e/\bar{\nu}_e$ appearance events for each experiment. We then study the effects of deviating the unknown parameters from the reference point and the compatibility of any given set of values of unknown parameters with the data from T2K and NO$\nu$A. T2K observes a large excess in the $\nu_e$ appearance event sample compared to the expected $\nu_e$ events at the reference point, whereas \nova observes a moderate excess. The large excess in T2K dictates that $\delta_{CP}$ be anchored at $-90^\circ$ and that $\theta_{23}>\pi/4$ with a preference for normal hierarchy. The moderate excess at NO$\nu$A leads to two degenerate solutions: A) NH, $0<\delta_{CP}<180^\circ$, and $\theta_{23}>\pi/4$; B) IH, $-180^\circ<\delta_{CP}<0$, and $\theta_{23}>\pi/4$. This is the main cause of the tension between the two experiments. We have reviewed the status of three beyond standard model (BSM) physics scenarios, (a) non-unitary mixing, (b) Lorentz invariance violation and (c) non-standard neutrino interactions, to resolve the tension., Comment: Review article, 59 pages, 17 figures, 7 tables

The latest data from the T2K and \nova experiments show a tension in their preferred values of the oscillation parameters. In this work, we try to identify the source of the tension between the data from these two experiments. An analysis of their data from various channels (individually, and combined) shows that the tension arises primarily from the $\nu_e$ appearance data, and is compounded by the $\bar{\nu}_\mu$ disappearance data. We provide an explanation for the tension based on parameter degeneracies. Apart from the analysis with the standard matter effect, we also analyse the data with the vacuum oscillation hypothesis. We find that vacuum oscillations fit the data as well as matter effects do; and also reduce the tension between the two experiments. We have also done a study of the future run of NO$\nu$A, T2K and DUNE in the context of resolving this tension., Comment: 32 pages, 13 figures, figures improved, reference updated, accepted in EPJC

In this paper, we have estimated the neutrino mass ordering and the CP violation sensitivity of the proposed Protvino to Orca (P2O) experiment after 6 years of data-taking. Both unitary and non-unitary $3\times 3$ neutrino mass mixing have been considered in the simulations. A forecast analysis deriving possible future constraints on non-unitary parameters at P2O have been performed., Comment: 26 pages, 18 figures, 2 tables

The $\nu_\mu \to \nu_e$ oscillation probability over short baseline ($\lesssim 1$~km) would be negligible in case the mixing matrix for three active neutrinos is unitary. However, in case of non-unitary mixing of three neutrinos, this probability would be non-negligible due to the so-called "zero distance" effect. Hence, the near detector of the accelerator experiments such as NO$\nu$A can provide strong constraints on the parameters of the non-unitary mixing with very large statistics. By analyzing the NO$\nu$A near detector data we find that the non-unitary mixing does not improve fits to the $\nu_e$ or $\nu_\mu$ events over the standard unitary mixing. This leads to constraints on the non-unitary parameters: $\alpha_{00}>0.911$, $|\alpha_{10}|<0.020$ and $\alpha_{11}>0.952$ at 90\% C.L. A combined analysis with the near and far detector data does not change these constraints significantly., Comment: 13 pages, 8 figures, data from the latest NOvA publication have been used, the systematics uncertainties have been updated, the result has changed drastically from the last version

In this paper, we have analysed the latest data from NO$\nu$A and T2K with the Lorentz invariance violation along with the standard oscillation hypothesis. We have found that the NO$\nu$A data cannot distinguish between the two hypotheses at $1\, \sigma$ confidence level. T2K data and the combined data analysis excluded standard oscillation at $1\, \sigma$. All three cases do not have any hierarchy sensitivity when analysed with LIV. There is a mild tension between the two experiments, when analysed with LIV, as $\theta_{23}$ at \nova best-fit is at higher octant but the same for T2K is at lower octant. NO$\nu$A has a new degeneracy over $\sin^2 \theta_{23}$ value, when analysed with LIV., Comment: 25 pages, 12 figures, Accepted in EPJC

We study the charged lepton flavour violation in a popular neutrino mass model with $A_4$ discrete symmetry. This symmetry requires the presence of multiple Higgs doublets in the model and it also dictates the flavour violating Yukawa couplings of the additional neutral scalars of the model. Such couplings lead to the decays of the neutral mesons, the top quark and the $\tau$ lepton into charged leptons of different flavours at tree level. The $A_4$ symmetry of the model leads to certain characteristic signatures in these decays. We discuss these signatures and predict the rates for the most favourable charged lepton flavour violating modes., Comment: 18 pages, Accepted in EPJC

The neutrino oscillation probabilities at the long-baseline accelerator neutrino experiments are expected to be modified by matter effects. We search for evidence of such modification in the data of T2K and NO$\nu$A, by fitting the data to the hypothesis of (a) matter modified oscillations and (b) vacuum oscillations. We find that vacuum oscillations provide as good a fit to the data as matter modified oscillations. Even extended runs of T2K and NO$\nu$A, with 5 years in neutrino mode $(5 \nu)$ and five years in anti-neutrino mode $(5 \bar{\nu})$, can {\bf not} make a $3~\sigma$ distinction between vacuum and matter modified oscillations. The proposed experiment DUNE, with neutrino and anti-neutrino runs of 5 years each $(5 \nu + 5 \bar{\nu})$, can rule out vacuum oscillations by itself at $5~\sigma$ if the hierarchy is normal. If the hierarchy is inverted, a $5~\sigma$ discrimination against vacuum oscillations requires the combination of $(5 \nu + 5 \bar{\nu})$ runs of T2K, \nova and DUNE., Comment: 12 pages, 4 figures

The mixing of three active neutrino flavors is parameterized by the unitary PMNS matrix. If there are more than three neutrino flavors and if the extra generations are heavy isosinglets, the effective $3\times 3$ mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and \nova data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NO$\nu$A data slightly (at $\sim 1\, \sigma$ C.L.) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the \nova best-fit point in the $\sin^2\theta_{23}-\delta_{CP}$ plane closer to the T2K best-fit point. The 2019 T2K data, on the other hand, cannot rule out any of the two mixing schemes. A combined analysis of the NO$\nu$A and T2K 2019 data prefers the non-unitary mixing at $1\, \sigma$ C.L.. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NO$\nu$A and T2K data. These constraints are weaker than previously found. The latest 2020 data from both the experiments prefer non-unitarity over unitary mixing at $1\, \sigma$ C.L. The combined analysis preferes non-unitarity at $2\, \sigma$ C.L. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis., Comment: 30 pages, 19 figures, 3 tables. Results for 2020 data from NOvA and T2K have been included, Accepted in EPJC

The long baseline neutrino experiments, T2K and NOvA, have taken significant amount of data in each of the four channels: (a) $\nu_\mu$ disappearance, (b) $\bar\nu_\mu$ disappearance (c) $\nu_e$ appearance and (d) $\bar\nu_e$ appearance. There is a mild tension between the disappearance and the appearance data sets of T2K. A more serious tension exists between the $\nu_e$ appearance data of T2K and the $\nu_e / \bar\nu_e$ appearance data of NOvA. This tension is significant enough that T2K rules out the best-fit point of NOvA at $95\%$ confidence level whereas NOvA rules out T2K best-fit point at $90\%$ confidence level. We explain the reason why these tensions arise. We also do a combined fit of T2K and NOvA data and comment on the results of this fit., Comment: matches the published version

The combined analysis of $\nu_\mu$ disappearance and $\nu_e$ appearance data of NO$\nu$A experiment leads to three nearly degenerate solutions. This degeneracy can be understood in terms of deviations in $\nu_e$ appearance signal, caused by unknown effects, with respect to the signal expected for a reference set of oscillations parameters. We define the reference set to be vacuum oscillations in the limit of maximal $\theta_{23}$ and no CP-violation. We then calculate the deviations induced in the $\nu_e$ appearance signal event rate by three unknown effects: (a) matter effects, due to normal or inverted hierarchy (b) octant effects, due to $\theta_{23}$ being in higher or lower octant and (c) CP-violation, whether $\delta_{CP} \sim - \pi/2$ or $\delta_{CP} \sim \pi/2$. We find that the deviation caused by each of these effects is the same for NO$\nu$A. The observed number of $\nu_e$ events in NO$\nu$A is equivalent to the increase caused by one of the effects. Therefore, the observed number of $\nu_e$ appearance events of NO$\nu$A is the net result of the increase caused by two of the unknown effects and the decrease caused by the third. Thus we get the three degenerate solutions. We also find that further data by NO$\nu$A can not distinguish between these degenerate solutions but addition of one year of neutrino run of DUNE can make a distinction between all three solutions. The distinction between the two NH solutions and the IH solution becomes possible because of the larger matter effect in DUNE. The distinction between the two NH solutions with different octants is a result of the synergy between the anti-neutrino data of NO$\nu$A and the neutrino data of DUNE., Comment: Published version v2; with minor changes to v1

We explore neutrino mass hierarchy determination and CP-phase measurement using multi-megaton water Cherenkov detector KM3NeT-Oscillation Research with Cosmics in the Abyss (ORCA) in the Mediterranean sea receiving neutrino beam from the Fermilab Long Baseline Neutrino Facility (LBNF) over 6900 km baseline. We find that with the proposed beam luminosity of $1.2\times 10^{21}$ proton-on-target per year, it will be possible to determine mass hierarchy at $\gtrsim 4\,\sigma$ confidence level within 1 year in the neutrino mode alone. A combined 1 year in neutrino and 1 year in antineutrino mode can determine hierarchy at $\gtrsim 6\,\sigma$ confidence level. We also find that a non-zero CP-phase can be detected with up to $\sim 1.8\,\sigma$ significance after 10 years of data taking. We explore degeneracy of neutrino oscillation parameters and uncertainties in detection efficiencies affecting the results., Comment: 9 pages, 10 figures, reanalysis resulting improved sensitivities to mass hierarchy and CP phase. Accepted in Phys. Rev. D

The $\nu_e$ appearance data of T2K experiment has given a glimpse of the allowed parameters in the hierarchy-$\delta_{CP}$ parameter space. In this paper, we explore how this data affects our expectations regarding the hierarchy sensitivity of the NO$\nu$A experiment. For the favourable combinations of hierarchy and $\delta_{CP}$, the hierarchy sensitivity of NO$\nu$A is unaffected by the addition of T2K data. For the unfavourable combinations, NO$\nu$A data gives degenerate solutions. Among these degenerate solutions, T2K data prefers IH and $\delta_{CP}$ in the lower half plane over NH and $\delta_{CP}$ in the upper half plane. Hence, addition of the T2K data to NO$\nu$A creates a bias towards IH and $\delta_{CP}$ in the lower half plane irrespective of what the true combination is., Comment: 22 pages, 14 figures

The moderately large value of $\ty$, measured recently by reactor experiments, is very welcome news for the future neutrino experiments. In particular, the \nova experiment, with 3 years each of $\nu$ and $\anu$ runs, will be able to determine the mass hierarchy if one of the following two favourable combinations is true: normal hierarchy with $-180^\circ \leq \dcp \leq 0$ or inverted hierarchy with $0\leq \dcp \leq 180^\circ$. In this report, we study the hierarchy reach of the first 3 years of \nova data. Since $\sin^2 2 \tz$ is measured to be non-maximal, $\tz$ can be either in the lower or higher octant. Pure $\nu$ data is affected by $\ty$-hierarchy and octant-hierarchy degeneracies, which limit the hierarchy sensitivity of such data. A combination of $\nu$ and $\anu$ data is not subject to these degeneracies and hence has much better hierarchy discrimination capability. We find that, with a 3 year $\nu$ run, hierarchy determination is possible for only two of the four octant-hierarchy combinations. Equal 1.5 year runs in $\nu$ and $\anu$ modes give good hierarchy sensitivity for all the four combinations.