Quantum correlations and the neutrino mass degeneracy problem

1999

In these two lectures I describe first the theory of neutrino mass and then discuss the implications of recent data (including 708-day data Super-Kamiokande data) which strongly indicate the need for neutrino conversions to account for the solar and atmospheric neutrino observations. I also mention the LSND data, which provides an intriguing hint. The simplest ways to reconcile all these data in terms of neutrino oscillations invoke a light sterile neutrino in addition to the three active ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND scale, while the others are at the solar mass scale. These schemes can be distinguished at neutral-current-sensitive solar & atmospheric neutrino experiments. I discuss the simplest theoretical scenarios, where the lightness of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and the generation of ∆m 2 ⊙ & ∆m 2 atm all follow naturally from the assumed lepton-number symmetry and its breaking. Although the most likely interpretation of the present data is in terms of neutrino-mass-induced oscillations, one still has room for alternative explanations, such as flavour changing neutrino interactions, with no need for neutrino mass or mixing. Such flavour violating transitions arise in theories with strictly massless neutrinos, and may lead to other sizeable flavour non-conservation effects, such as µ → e + γ, µ − e conversion in nuclei, unaccompanied by neutrino-less double beta decay.

2007

I try to give an overview of future prospects of the experimental exploration of the unknowns in the neutrino mass pattern and the lepton flavor mixing. Because of the nature of the lectures on which this manuscript is based, I give some pedagogical discussions to prepare for the presentation in the later part. I start from measuring θ 13 by reactors and accelerators as a prerequisite for proceeding to search for leptonic CP violation. I then discuss how CP violation can be uncovered, and how the neutrino mass hierarchy can be determined. I do these by resolving so called the "parameter degeneracy" which is necessary anyway if one wants to seek precision measurement of the lepton mixing parameters. As a concrete setting for resolving the degeneracy I introduce the Tokai-to-Kamioka-Korea two detector complex which receives neutrino superbeam from J-PARC, sometimes dubbed as "T2KK". It is shown that T2KK is able to resolve all the eight-fold parameter degeneracy in a wide range of the lepton mixing parameters. I also discuss an alternative way for lifting the θ 23 octant degeneracy by reactor-accelerator combined method. Finally, I discuss by taking some examples how some theoretically or phenomenologically motivated ideas can be tested experimentally.

Physical Review D, 1999

We consider ν µ → ν e oscillations in long baseline experiments within a three flavor oscillation framework. A non-zero measurement of this oscillation probability implies that the (13) mixing angle φ is non-zero. We consider the effect of neutrino propagation through the matter of earth's crust and show that, given the constraints from solar neutrino and CHOOZ data, matter effects enhance the mixing for neutrinos rather than for anti-neutrinos. We need data from two different experiments with different baseline lengths (such as K2K and MINOS) to distinguish matter effects unambiguously.

Journal of High Energy Physics, 2019

We perform a global analysis of neutrino data in the framework of three massive neutrinos with non-standard neutrino interactions which affect their evolution in the matter background. We focus on the effect of NSI in the present observables sensitive to leptonic CP violation and to the mass ordering. We consider complex neutral current neutrino interactions with quarks whose lepton-flavor structure is independent of the quark type. We quantify the status of the "hints" for CP violation, the mass-ordering and non-maximality of θ 23 in these scenarios. We also present a parametrization-invariant formalism for leptonic CP violation in presence of a generalized matter potential induced by NSI.

Springer Tracts in Modern Physics, 2000

A review of the problem of neutrino mass, mixing and oscillations is given. Possible phenomenological schemes of neutrino mixing are discussed. The most important consequences of neutrino mixing-neutrino oscillations are considered in some details. The data of atmospheric, solar and LSND experiments are discussed. The results of phenomenological analyses of the data under the assumption of the mixing of three and four massive neutrinos are shortly presented.

Springer Proceedings in Physics, 2020

We study the effects of non-standard neutrino matter interactions on the coherence of oscillating neutrino-system in a model independent way in the context of upcoming DUNE experiment. We find that the LMA-LIGHT solution (with normal ordering of mass eigenstates) decreases the coherence in the system in comparison to the standard model prediction for almost all values of neutrino energy E and C P violating phase δ. However, a large enhancement in coherence parameter in the entire (E − δ) plane is possible for the DARK octant of θ 12 for inverted ordering, with a protuberant enhancement at E ∼ 4 GeV, where maximum neutrino flux is expected in the DUNE experiment. Such features make neutrino a promising candidate for carrying out quantum information theoretic tasks.

2018

Precision measurements of the neutrino mixing parameters, made over the past few decades has significantly shortened the list of unanswered questions in the standard scenario to just the issues of the neutrino mass hierarchy i.e., sign(δm31), the CP phase and the correct octant for the mixing angle θ23. While the simplest way to generate neutrino masses is to add right handed neutrino fields to the Standard Model (SM) particle content, it is hard to explain their extreme smallness. Several scenarios going beyond the SM have been proposed to this end, often tying up with other unanswered questions such as (electroweak) leptogenesis [1, 2], neutrino magnetic moments [3–6], neutrino condensate as dark energy [7, 8]. An agnostic alternative is to add dimension-five terms consistent with the symmetries and particle content of the SM, which naturally leads to desired tiny Majorana masses for the left-handed neutrinos. Irrespective of the approach, once new physics is invoked to explain th...

1999

Theory suggests the existence of neutrino masses, but little more. Facts are coming close to reveal our fantasy: solar and atmospheric neutrino data strongly indicate the need for neutrino conversions, while LSND provides an intriguing hint. The simplest ways to reconcile these data in terms of neutrino oscillations invoke a light sterile neutrino in addition to the three active ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND scale, while the others are at the solar mass scale. These schemes can be distinguished at neutral-current-sensitive solar & atmospheric neutrino experiments. I discuss the simplest theoretical scenarios, where the lightness of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and the generation of ∆m 2 ⊙ & ∆m 2 atm all follow naturally from the assumed lepton-number symmetry and its breaking. Although the most likely interpretation of the present data is in terms of neutrino-mass-induced oscillations, one still has room for alternative explanations, such as flavour changing neutrino interactions, with no need for neutrino mass or mixing. Such flavour violating transitions arise in theories with strictly massless neutrinos, and may lead to other sizeable flavour non-conservation effects, such as µ → e + γ, µ − e conversion in nuclei, unaccompanied by neutrinoless double beta decay.

New Journal of Physics, 2014

The origin of fermion mass hierarchies and mixings is one of the unresolved and most difficult problem in high-energy physics. One possibility to address the flavour problem is by extending the Standard Model to include a family symmetry. In the recent years it has become very popular to use non-Abelian discrete flavour symmetries because of their power in the prediction of the large leptonic mixing angles relevant for neutrino oscillation experiments. Here we give an introduction to the flavour problem and to discrete groups which have been used to attempt a solution for it. We review the current status of models in the light of the recent measurement of the reactor angle and we consider different model building directions taken. The use of the flavons or multi Higgs scalars in model building is discussed as well as the direct vs. indirect approaches. We also focus on the possibility to distinguish experimentally flavour symmetry models by means of mixing sum rules and mass sum rules. In fact, we illustrate in this review the complete path from mathematics, via model building, to experiments, so that any reader interested to start working in the field could use this text as a starting point in order to get a broad overview of the different subject areas.

The European Physical Journal C

Effects of physics beyond the standard model in the neutrino sector are conveniently incorporated through non-standard interaction parameters. Assuming new physics in the form of dimension-6 vector operators, a recent global analysis of neutrino oscillation data including results from COHERENT experiment suggests two favourable new physics scenarios. These are LMA-Light (with normal mass ordering) and LMA-Dark (with inverted mass ordering) sectors of parameters. In this work, we study the effects of new physics solutions on Leggett–Garg-type (LGtI) inequality which quantifies temporal correlations in the system along with flavour entropy and genuine tripartite entanglement which can be considered as measures of spatial correlations. We show that the violation of LGtI for $$\nu _{\mu }$$ ν μ energy around 3 GeV in the DUNE experimental set-up can not only be an indication of presence of new physics but such a new physics is expected to be in the form of LMA-Dark sector with inverted ...