G. Rajasekaran

Softly broken A(4) symmetry for nearly degenerate neutrino masses

The leptonic Higgs doublet model of neutrino masses is implemented with an A 4 discrete symmetry (the even permutation of four objects or equivalently the symmetry of the tetrahedron) which has four 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. The phenomenological consequences at and below the TeV scale are discussed.

Observing the Dark Scalar Doublet and its Impact on the Standard-Model Higgs Boson at Colliders

If the standard model of particle interactions is extended to include a second scalar doublet [H{sup +},(H{sup 0}+iA{sup 0})/{radical}(2)], which is odd under an unbroken Z{sub 2} discrete symmetry, it may be called the dark scalar doublet, because its lightest neutral member, say H{sup 0}, is one possible component for the dark matter of the Universe. We discuss the general phenomenology of the four particles of this doublet, without assuming that H{sup 0} is the dominant source of dark matter. We also consider the impact of this dark scalar doublet on the phenomenology of the standard-model Higgs boson h.

High scale mixing unification and large neutrino mixing angles

Starting with the hypothesis that quark and lepton mixings are identical at or near the grand unified theory scale, we show that the large solar and atmospheric neutrino mixing angles together with the small reactor angle U e3 can be understood purely as a result of renormalization group evolution provided the three neutrinos are quasidegenerate and have the same CP parity. The mechanism is found to work if the common Majorana mass for the neutrinos is larger than 0.1 eV, which falls right in the range reported recently and also in the range which will be probed in planned experiments.

Colour gluons and scaling in a unified gauge model

Deep inelastic weak and electromagnetic processes are considered within the parton framework taking the partons to be integrally charged quarks and coloured gluons. Despite the participation of the spin-one gluons in these processes, scaling is shown to be maintained by treating the problem in a unified gauge model based on the groupSU (3)colour⊗SUL (2)⊗U(1). This is a consequence of the vector-dominance type of couplings between the gluons and the weak or electromagnetic vector bosons which are induced by the spontaneous breakdown of gauge symmetry. As a further consequence it is found that in the asymptotic region far above the gluon masses the colour octet parts of the weak and electromagnetic currents of the quarks are damped so that, in particular, the integrally charged quarks behave as fractionally charged quarks in this region.

Neutrino oscillation probabilities: Sensitivity to parameters

We study in detail the sensitivity of neutrino oscillation probabilities to the fundamental neutrino parameters and their possible determination through experiments. The first part of the paper is devoted to the broad theme of isolating regions in the neutrino (and antineutrino) energy and propagation length that are sensitive to the oscillation parameters. Such a study is relevant to neutrinos both from the Earths atmosphere or from a neutrino factory. For completeness we discuss the sensitivity, however small, to the parameters involved in a three-generation framework, and to the Earth matter density profile. We then study processes relevant to atmospheric neutrinos which are sensitive to and allow precision measurements of the mixing angle

Three inequivalent mass-degenerate Majorana neutrinos and a scenario of their splitting for neutrino oscillations

{\ensuremath{\theta}}_{23}

Hans Bethe, the sun and the neutrinos

and mass-squared difference

Neutrino Mixings and Leptonic CP Violation from CKM Matrix and Majorana Phases

{\ensuremath{\delta}}_{32}

Orthosupersymmetric quantum mechanics

apart from the mixing angle

New “square root” model of lepton family cyclic symmetry

{\ensuremath{\theta}}_{13}