Rathin Adhikari

Light neutrinos from massless texture and below TeV seesaw scale

We present general conditions on Dirac and Majorana mass terms under which a type-I seesaw mechanism can lead to three exactly massless neutrinos at the tree level. We depict several examples where the conditions are satisfied and relate some of them to an underlying U(1) symmetry. We show that higher order corrections may generate the small observed masses and this may be achieved even when the heavy Majorana neutrinos are at the electroweak scale or a little higher.

Can R-parity violating supersymmetry be seen in long baseline beta-beam experiments?

Abstract Long baseline oscillation experiments may well emerge as test beds for neutrino interactions as are present in R-parity violating supersymmetry. We show that flavour diagonal (FDNC) and flavour changing (FCNC) neutral currents arising therefrom prominently impact a neutrino β-beam experiment with the source at CERN and the detector at the proposed India-based Neutrino Observatory. These interactions may preclude any improvement of the present limit on θ 13 and cloud the hierarchy determination unless the upper bounds on R couplings, particularly λ ′ , become significantly tighter. If R interactions are independently established then from the event rate a lower bound on θ 13 may be set. We show that there is scope to see a clear signal of non-standard FCNC and FDNC interactions, particularly in the inverted hierarchy scenario and also sometimes for the normal hierarchy. In favourable cases, it may be possible to set lower and upper bounds on λ ′ couplings. FCNC and FDNC interactions due to λ type R couplings are unimportant.

LSND, solar and atmospheric neutrino oscillation experiments, and R -parity violating supersymmetry

With only three flavors it is possible to account for various neutrino oscillation experiments. The masses and mixing angles for three neutrinos can be determined from the available experimental data on neutrino oscillation and from astrophysical arguments. We have shown here that such masses and mixing angles which can explain the atmospheric neutrino anomaly, LSND result, and the solar neutrino experimental data, can be reconciled with the R-parity violating supersymmetric models through lepton-number-violating interactions. We have estimated the order of magnitude for some lepton-number-violating couplings. Our analysis indicates that lepton number violation is likely to be observed in near future experiments. From the data on neutrino oscillation and the electric dipole moment of electron, under some circumstances it is possible to obtain a constraint on the complex phase of some supersymmetry breaking parameters in R-parity-violating supersymmetric models.

BARYOGENESIS IN A SUPERSYMMETRIC MODEL WITHOUT R-PARITY

We propose a simple scenario for baryogenesis in supersymmetric models where baryon number is broken alongwith R-parity. The lightest supersymmetric particle (neutralino) decays to three quarks and CP-violation comes from interference of tree and one loop box diagrams. The bounds on the R-parity breaking couplings from the out-of-equilibrium condition are considerably relaxed in this scenario.

Constraints on mixing angles of Majorana neutrinos

By combining the inputs from the neutrinoless double beta decay and the fits of cosmological models of dark matter with solar and atmospheric neutrino data, we obtain constraints on two of the mixing angles of Majorana neutrinos, which become stronger when coupled with the reactor neutrino data. These constraints are strong enough to rule out Majorana neutrinos if the small angle solution of solar neutrino puzzle is borne out.

Common origin of the 3.55 keV x-ray line and the Galactic Center gamma-ray excess in a radiative neutrino mass model

We attempt to simultaneously explain the recently observed 3.55 keV X-ray line in the analysis of XMM-Newton telescope data and the galactic center gamma ray excess observed by the Fermi gamma ray space telescope within an abelian gauge extension of standard model. We consider a two component dark matter scenario with tree level mass difference 3.55 keV such that the heavier one can decay into the lighter one and a photon with energy 3.55 keV. The lighter dark matter candidate is protected from decaying into the standard model particles by a remnant

The discovery reach of CP violation in neutrino oscillation with non-standard interaction effects

Z_2

Baryogenesis through R -parity violation

symmetry into which the abelian gauge symmetry gets spontaneously broken. If the mass of the dark matter particle is chosen to be within

Distinctive signals of spontaneous R-parity breaking at LEP-II

31-40

Light neutralinos in B decays.

GeV, then this model can also explain the galactic center gamma ray excess if the dark matter annihilation into