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Register a new userInterpretation of NO$ u$A and T2K data in the presence of a light sterile neutrino
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We study in detail the impact of a light sterile neutrino in the interpretation of the latest data of the long baseline experiments NO$ u$A and T2K, assessing the robustness/fragility of the estimates of the standard 3-flavor parameters with respect to the perturbations induced in the 3+1 scheme. We find that all the basic features of the 3-flavor analysis, including the weak indication ($sim$1.4$sigma$) in favor of the inverted neutrino mass ordering, the preference for values of the CP-phase $delta_{13} sim 1.2pi$, and the substantial degeneracy of the two octants of $theta_{23}$, all remain basically unaltered in the 4-flavor scheme. Our analysis also demonstrates that it is possible to attain some constraints on the new CP-phase $delta_{14}$. Finally, we point out that, differently from non-standard neutrino interactions, light sterile neutrinos are not capable to alleviate the tension recently emerged between NO$ u$A and T2K in the appearance channel.
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We study the impact of one light sterile neutrino on the prospective data expected to come from the two presently running long-baseline experiments T2K and NOvA when they will accumulate their full planned exposure. Introducing for the first time, the bi-probability representation in the 4-flavor framework, commonly used in the 3-flavor scenario, we present a detailed discussion of the behavior of the numu to nue and numubar to nuebar transition probabilities in the 3+1 scheme. We also perform a detailed sensitivity study of these two experiments (both in the stand-alone and combined modes) to assess their discovery reach in the presence of a light sterile neutrino. For realistic benchmark values of the mass-mixing parameters (as inferred from the existing global short-baseline fits), we find that the performance of both these experiments in claiming the discovery of the CP-violation induced by the standard CP-phase delta13 equivalent to delta, and the neutrino mass hierarchy get substantially deteriorated. The exact loss of sensitivity depends on the value of the unknown CP-phase delta14. Finally, we estimate the discovery potential of total CP-violation (i.e., induced simultaneously by the two CP-phases delta13 and delta14), and the capability of the two experiments of reconstructing the true values of such CP-phases. The typical (1 sigma level) uncertainties on the reconstructed phases are approximately 40 degree for delta13 and 50 degree for delta14.
ESS$ u$SB is a proposed neutrino super-beam project at the ESS facility. We study the performance of this setup in the presence of a light eV-scale sterile neutrino, considering 540 km baseline with 2 years (8 years) of $ u$ ($bar u$) run-plan. This baseline offers the possibility to work around the second oscillation maximum, providing high sensitivity towards CP-violation (CPV). We explore in detail its capability in resolving CPV generated by the standard CP phase $delta_{13}$, the new CP phase $delta_{14}$, and the octant of $theta_{23}$. We find that the sensitivity to CPV induced by $delta_{13}$ deteriorates noticeably when going from $3 u$ to 4$ u$ case. The two phases $delta_{13}$ and $delta_{14}$ can be reconstructed with a 1$sigma$ uncertainty of $sim15^0$ and $ sim35^0$ respectively. Concerning the octant of $theta_{23}$, we find poor sensitivity in both $3 u$ and $4 u$ schemes. Our results show that a setup like ESS$ u$SB working around the second oscillation maximum with a baseline of 540 km, performs quite well to explore CPV in 3$ u$ scheme, but it is not optimal for studying CP properties in 3+1 scheme.
The first hint of neutrino mass hierarchy is expected to come from the NO$ u$A experiment in Fermilab as the present best-fit parameter space i.e., normal hierarchy and $delta_{CP}=-90^circ$ is the favourable parameter space for NO$ u$A where there is no degeneracy. But this situation may change if the standard three flavour framework is not complete and there is existence of new physics. In this work we consider the presence of an extra light sterile neutrino at the eV scale and study the new degeneracies which are absent in the standard three flavour framework. We also study the effect of these new degeneracies on the hierarchy measurement of NO$ u$A.
The $ u_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$ u$A experiment. For the favourable combinations of hierarchy and $delta_{CP}$, the hierarchy sensitivity of NO$ u$A is unaffected by the addition of T2K data. For the unfavourable combinations, NO$ u$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$ u$A creates a bias towards IH and $delta_{CP}$ in the lower half plane irrespective of what the true combination is.
We investigate the performance of T2HK in the presence of a light eV scale sterile neutrino. We study in detail its influence in resolving fundamental issues like mass hierarchy, CP-violation (CPV) induced by the standard CP-phase $delta_{13}$ and new CP-phase $delta_{14}$, and the octant ambiguity of $theta_{23}$. We show for the first time in detail that due to the impressive energy reconstruction capabilities of T2HK, the available spectral information plays an important role to enhance the mass hierarchy discovery reach of this experiment in 3$ u$ framework and also to keep it almost intact even in $4 u$ scheme. This feature is also of the utmost importance in establishing the CPV due to $delta_{14}$. As far as the sensitivity to CPV due to $delta_{13}$ is concerned, it does not change much going from $3 u$ to 4$ u$ case. We also examine the reconstruction capability of the two phases $delta_{13}$ and $delta_{14}$, and find that the typical 1$sigma$ uncertainty on $delta_{13}$ ($delta_{14}$) in T2HK is $sim15^0$ ($30^0$). While determining the octant of $theta_{23}$, we face a complete loss of sensitivity for unfavorable combinations of unknown $delta_{13}$ and $delta_{14}$.
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