Bilarge neutrino mixing in R-parity violating supersymmetry: the role of right-chiral neutrino superfields

We consider the possibility of neutrino mass generation in a supersymmetric model where lepton number can be violated by odd units. The different patterns of mixing in the quark and lepton sectors are attributed to the persence of right-chiral neutrino superfields which (a) enter into Yukawa couplings via non-renormalizable interaction with hidden sector fields, and (b) can violate lepton number by odd units. Both of these features are shown to be the result of some global quantum number which is violated when SUSY is broken in the hidden sector. It is shown how such a scenario, together with all known R-parity violating effects, can lead to neutrino masses and bilarge mixing via seesaw as well as radiative mechanisms. Some sample values of the various parameters involved, consistent with electroweak symmetry breaking constraints, are presented as illustrations.Comment: 19 pages. Minor modificaitons are made in the text. This version is to appear in Physical Review

Invisibly decaying Higgs boson in the Littlest Higgs model with T-parity

We show that there are regions in the parameter space of the Littlest Higgs model with T-parity, allowed by electroweak precision data, where the Higgs boson can decay invisibly into a pair of heavy photons A_H with a substantial branching ratio. For a symmetry breaking scale f in the range 450-600 GeV, the BR(H -> A_H A_H) can be up to 95% for an intermediate mass Higgs, and from 20% down to a few percents for a Higgs boson of mass 200 GeV or above. The total decay width of the Higgs boson can thereby be enhanced by an order of magnitude compared to the Standard Model for Higgs masses around 130 GeV.Comment: 4 pages, 2 figures, Latex (stylefiles included); Talk presented by A.N. at the International Workshop on Theoretical High Energy Physics (IWTHEP 2007), Roorkee, India, 15-20 March 2007, to appear in the proceeding

Parity violation in four and higher dimensional spacetime with torsion

The possibility of parity violation in a gravitational theory with torsion is extensively explored in four and higher dimensions. In the former case,we have listed our conclusions on when and whether parity ceases to be conserved, with both two-and three-index antisymmetry of the torsion field. In the latter, the bulk spacetime is assumed to have torsion, and the survival of parity-violating terms in the four dimensional effective action is studied, using the compactification schemes proposed by Arkani-Hamed-Dimopoulos-Dvali and Randall-Sundrum. An interesting conclusion is that the torsion-axion duality arising in a stringy scenario via the second rank antisymmetric Kalb-Ramond field leads to conservation of parity in the gravity sector in any dimension. However, parity-violating interactions do appear for spin 1/2 fermions in such theories, which can have crucial phenomenological implications.Comment: 13 Pages, Latex, Title changed and thoroughly revised. To appear in Eur.Phys.J.

New Higgs signals from vector boson fusion in R-parity violating supersymmetry

We investigate signals of the lightest neutral Higgs in an R-parity violating supersymmetic model through the vector boson fusion mechanism. Assuming that R-parity is violated through lepton number, and locating regions in the parameter space where decays of such a neutral scalar into a pair of lightest neutralinos can be significant, we proceed to calculate the event rates for final states arising from decays of the neutralinos through both $\lambda$-and $\lambda'$-type interactions. Regions of the parameter space where each of these types of interactions can lead to detectable events are identified. It is found that over a sizable region, one can obtain useful signals of an intermediate mass neutral scalar from a study of the suggested final states at the Large Hadronic Collider

Bulk antisymmetric tensor fields in a Randall-Sundrum model

We consider bulk antisymmetric tensor fields of various ranks in a Randall-Sundrum scenario. We show that, rank-2 onwards, the zero-modes of the projections of these fields on the (3+1) dimensional visible brane become increasingly weaker as the rank of the tensor increases. All such tensor fields of rank 4 or more are absent from the dynamics in four dimensions. This leaves only the zero-mode graviton to have coupling $\sim 1/M_P$ with matter, thus explaining why the large-scale behaviour of the universe is governed by gravity only. We have also computed the masses of the heavier modes upto rank-3, and shown that they are relatively less likely to have detectable accelerator signals.Comment: 8 Pages, Late

Associated single photons and doubly charged scalar at linear e-e- colliders

Doubly charged scalars, predicted in many models having exotic Higgs representations, can in general have lepton-number violating (LFV) couplings. We show that by using an associated monoenergetic final state photon seen at a future linear e-e- collider, we can have a clear and distinct signature for a doubly-charged resonance. The strength of the Delta L=2 coupling can also be probed quite effectively as a function of the recoil mass of the doubly-charged scalar.Comment: Reference adde

Unitarity violation in sequential neutrino mixing in a model of extra dimensions

We investigate the possibility of unitarity violation in the sequential neutrino mixing matrix in a scenario with extra compact spacelike dimensions. Gauge singlet neutrinos are assumed to propagate in one extra dimension, giving rise to an infinite tower of states in the effective four-dimensional theory. It is shown that this leads to small lepton-number violating entries in the neutrino mass matrix, which can violate unitarity on the order of one per cent.Comment: 16 pages, 2 table

Invisible charginos and neutralinos from gauge boson fusion: a way to explore anomaly mediation ?

We point out that vector boson fusion (VBF) at the Large Hadron Collider (LHC) can lead to useful signals for charginos and neutralinos in supersymmetric scenarios where these particles are almost invisible. The proposed signals are just two forward jets with missing transverse energy. It is shown that in this way one can probe a large region of the parameter space of a theory with anomaly mediated supersymmtery breaking (AMSB) at the LHC. In addition, scenarios where the lightest neutralinos and charginos are Higgsino-like can give copious signals of the above type