The three massless active (doublet) neutrinos may mix with two heavy and one light sterile (singlet) neutrinos so that the induced masses and mixings among the former are able to explain the present data on atmospheric and solar neutrino oscillations. If the LSND result is also to be explained, one active neutrino mass eigenstate must mix with the light sterile neutrino. A specific model is proposed with the spontaneous and soft explicit breaking of a new global U (1) S symmetry so that a sterile neutrino will decay into an active antineutrino and a nearly massless pseudo-Majoron.

The leptonic Higgs doublet model of neutrino masses is implemented with an A 4 discrete symmetry (the even permutation of 4 objects or equivalently the symmetry of the tetrahedron) which has 4 irreducible representations: 1, 1 ′ , 1 ′′ , and 3. The resulting spontaneous and soft breaking of A 4 provides a realistic model of charged-lepton masses as well as a nearly degenerate neutrino mass matrix.

If the Standard Model (SM) of particle interactions is extended to include a second scalar doublet, which is odd under an unbroken Z 2 discrete symmetry, it may be called the dark scalar doublet, because its lightest neutral member, say H 0 , is one posssible component for the dark matter of the Universe. We discuss the general phenomenology of the four particles of this doublet, without assuming that H 0 is the dominant source of dark matter. We also consider the impact of this dark scalar doublet on the phenomenology of the SM Higgs boson h.

No abstract

Starting with the hypothesis that quark and lepton mixings are identical at or near the GUT scale, we show that the large solar and atmospheric neutrino mixing angles together with the small reactor angle Ue3 can be understood purely as a result of renormalization group evolution provided the three neutrinos are quasi-degenerate and have same CP parity. It predicts the common Majorana mass for the neutrinos larger than 0.1 eV, which falls right in the range reported recently and also the range which will be probed in the planned experiments.

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles. v Physics Potential of ICAL at INO vi PrefaceThe past two decades in neutrino physics have been very eventful, and have established this field as one of the flourishing areas of high energy physics. Starting from the confirmation of neutrino oscillations that resolved the decades-old problems of the solar and atmospheric neutrinos, we have now been able to show that neutrinos have nonzero masses, and different flavors of neutrinos mix among themselves. Our understanding of neutrino properties has increased by leaps and bounds. Many experiments have been constructed and envisaged to explore different facets of neutrinos, in particular their masses and mixing.The Iron Calorimeter (ICAL) experiment at the India-based Neutrino Observatory (INO) [1] is one of the major detectors that is expected to see the light of the day soon. It will have unique features like the ability to distinguish muon neutrinos from antineutrinos at GeV energies, and measure the energies of hadrons in the same energy range. It is therefore well suited for the identification of neutrino mass hierarchy, the measurement of neutrino mixing parameters, and many probes of new physics. The site for the INO has been identified, and the construction is expected to start soon. In the meanwhile, the R&D for the ICAL detector, including the design of its modules, the magnet coils, the active detector elements and the associated electronics, has been underway over the past deca...

No abstract

The high scale mixing unification hypothesis recently proposed by three of us (R. N. M., M. K. P. and G. R.) states that if at the seesaw scale, the quark and lepton mixing matrices are equal then for quasi-degenerate neutrinos, radiative corrections can lead to large solar and atmospheric mixings and small reactor angle at the weak scale in agreement with data. Evidence for quasidegenerate neutrinos could, within this framework, be interpreted as being consistent with quarklepton unification at high scale. In the current work, we extend this model to show that the hypothesis works quite successfully in the presence of CP violating phases (which were set to zero in the first paper). In the case where the PMNS matrix is identical to the CKM matrix at the seesaw scale, with a Dirac phase but no Majorana phase, the low energy Dirac phase is predicted to be (≃ 0.3 • ) and leptonic CP-violation parameter JCP ≃ (4 − 8) × 10 −5 and θ13 = 3.5 • . If on the other hand, the PMNS matrix is assumed to also have non-negligible Majorana phase(s) initially, the resulting theory damps radiative magnification phenomenon for a large range of parameters but nevertheless has enough parameter space to give the two necessary large neutrino mixing angles. In this case, one has θ13 = 3.5 • − 10 • and |JCP | as large as 0.02 − 0.04 which are accessible to long baseline neutrino oscillation experiments.PACS numbers: 14.60. Pq, 11.30.Hv, 12.15.Lk I INTRODUCTIONGrand unified theories [1][2][3][4] with quark-lepton unification have often been used as key ingredients in attempts to understand the widely differing values of physical parameters describing particle interactions at low energies. In the context of SUSY GUTs, this approach can explain the experimentally measured values of the electro-weak mixing angle. The same models also lead to b − τ Yukawa unification [5] which seems to be in rough agreement with observation or even t − b − τ Yukawa unification [6] which agree with observation for large values of tan β(= v u /v d ). It is then natural to explore whether there are other manifestations of quark lepton unification at low energies.In a recent paper, three of us [7] discussed the possibility that weak interaction properties of quarks and leptons parameterized by very different flavor mixing matrices at low energies may become identical at high scales and provide another signature of quark-lepton unification. We found that if neutrinos are Majorana fermions with quasidegenerate masses and with same CP, it could indeed happen i.e. starting with the CKM mixing matrix for neutrinos at the GUT-seesaw scale [8], as would be expected on the basis of quark-lepton unification [1], renormalization group evolution (RGE) to the weak scale leads to predictions for neutrino mixings in agreement with observations [10]. Since small angles become larger, we have called this phenomenon radiative magnification and the interesting result is that the RGEs give two large mixings in the solar and atmospheric neutrino sectors while ultra smallness of V ub...