Related papers: Experimental and Theoretical Implications of New S…
A search for the pair-production of heavy leptons ($N^0,L^{\pm}$) predicted by the type-III seesaw theory formulated to explain the origin of small neutrino masses is presented. The decay channels $N^0\rightarrow W^{\pm}l^{\mp}$ ($\ell = e,…
We discuss the scenario with gauge singlet fermions (right-handed neutrinos) accessible at the energy of the Large Hadron Collider. The singlet fermions generate tiny neutrino masses via the seesaw mechanism and also have sizable couplings…
There exist tree-level generalizations of the Type-I and Type-III seesaw mechanisms that realize neutrino mass via low-energy effective operators with d>5. However, these generalizations also give radiative masses that can dominate the…
In the minimal Standard Model (MSM) with three generations of quarks and leptons, neutrinos can have tiny charges consistent with electromagnetic gauge invariance. There are three types of non-standard electric charge, given by $Q_{st} +…
The heavier chargino decay could yield two charged leptons of different generations, owing to generation mixing of sneutrinos. We discuss the possibility of producing $e$ and $\mu$ through this process in near future collider experiments.…
We propose an anomaly free gauged U$(1)$ extension of the SM where three right handed heavy neutrinos, being charged under the general U$(1)$ gauge group, are introduced to explain the origin of the tiny neutrino mass through the seesaw…
We examine two processes, the neutrino production process e^+e^- ---> N\nu and the inverse neutrinoless double-beta decay process e^-e^- --->W^-W^- as possible places for discovering heavy neutrinos in future lepton linear colliders. The…
A natural seesaw mechanism for obtaining the observed size of SM neutrino masses can arise in a warped extra dimensional/composite Higgs framework. In a previous paper, we initiated the study of signals at the LHC for the associated $\sim$…
The small neutrino mass observed in neutrino oscillations is nicely explained by the seesaw mechanism. Rich phenomenology is generally expected if the heavy neutrinos are not much heavier than the electroweak scale. A model with this…
We consider the contributions to $g_\mu-2$ from fourth generation heavy neutral and charged leptons, $N$ and $E$, at the one-loop level. Diagrammatically, there are two types of contributions: boson-boson-$N$, and $E$-$E$-boson in the loop…
Observation of non-zero neutrino masses at a scale $\sim 10^{-1} - 10^{-2}$ eV is a major problem in the otherwise highly successful Standard Model. The most elegant mechanism to explain such tiny neutrino masses is the seesaw mechanism…
The existence of tiny neutrino masses at a scale more than a million times smaller than the lightest charged fermion mass, namely the electron, and their mixings can not be explained within the framework of the exceptionally successful…
We derive limits on a class of new physics effects that are naturally present in grand unified theories based on extended gauge groups, and in particular in $E_6$ and $SO(10)$ models. We concentrate on $i$) the effects of the mixing of new…
The inclusion of heavy neutral leptons (right-handed neutrinos) to the Standard Model (SM) particle content is one of the best motivated ways to account for the observed neutrino masses and flavor mixing. The modification of the charged and…
Upper bounds on the CP asymmetry relevant for leptogenesis are reexamined and found weaker than in previous literature, both for hierarchical and for quasi-degenerate right-handed neutrinos. Successful leptogenesis implies the usual lower…
Extending the Standard Model (SM) with sterile ('right-handed') neutrinos is one of the best motivated ways to account for the observed neutrino masses. We discuss the expected sensitivity of future lepton collider experiments for probing…
Doubly charged excited leptons give rise to interesting signatures for physics beyond the standard model at the present Large Hadron Collider. These exotic states are introduced in extended isospin multiplets which couple to the ordinary…
Searches for unstable neutral and charged heavy leptons, N and L+-, and for excited states of neutral and charged leptons, nu*, e*, mu*, and tau*, have been performed in e+e- collisions using data collected by the OPAL detector at LEP. The…
We update present bounds on the helicity of the neutrinos produced in muon decay, including e+ e- -> fbar f LEP 2 data. These significantly reduce the limits derived from all the other electroweak precision data. In Standard Model…
We present a benchmark in the parameter space of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) that provides for a dramatic multi-lepton signal and no jets containing 5 or more leptons resulting from the cascade decays of the…