A. J. Ramalho

Discriminating among the theoretical origins of new heavy Majorana neutrinos at CERN LHC

A study on the possibility of distinguishing new heavy Majorana neutrino models at LHC energies is presented. The experimental confirmation of standard neutrinos with nonzero mass and the theoretical possibility of lepton number violation find a natural explanation when new heavy Majorana neutrinos exist. These new neutrinos appear in models with new right-handed singlets, in new doublets of some grand unified theories and left-right symmetrical models. It is expected that signals of new particles can be found at the CERN high-energy hadron collider (LHC). We present signatures and distributions that can indicate the theoretical origin of these new particles. The single and pair production of heavy Majorana neutrinos are calculated and the model dependence is discussed. Same-sign dileptons in the final state provide a clear signal for the Majorana nature of heavy neutrinos, since there is lepton number violation. Mass bounds on heavy Majorana neutrinos allowing model discrimination are estimated for three different LHC luminosities.

Minimal left-right symmetric models and new Z' properties at future electron-positron colliders

Abstract.It was recently shown that left-right symmetric models for elementary particles can be built with only two Higgs doublets. The general consequence of these models is that the left and right fermionic sectors can be connected by a new neutral gauge boson Z’ having its mass as the only additional new parameter. In this paper we study the influence of the fundamental fermionic representation for this new neutral gauge boson. Signals of possible new heavy neutral gauge bosons are investigated for the future electron-positron colliders at

Single heavy lepton production in high energy electron-positron collisions

\sqrt s = 500

Bounds on the electromagnetic interactions of excited spin-3/2 leptons

GeV, 1 TeV and 3 TeV. The total cross sections, forward-backward and left-right asymmetries and model differences are calculated for the process

Production and decay of single heavy spin-3/2 leptons in high energy electron-positron collisions.

e^ + e^- \longrightarrow \mu^ + \mu^-

Spin-32 lepton production at HERA

. Bounds on Z’ masses are estimated.

On new gauge boson signals according to the littlest higgs model in future e+ e- colliders

The production and decay of exotic leptons are discussed in the context of the vector singlet, vector doublet, and fermion mirror-fermion models, at c.m. energies {radical}{ital s} =190 GeV (CERN LEP II) and {radical}{ital s} =500 GeV (NLC). The model dependence of total cross sections and kinematic distributions at these energies is shown to be weak for these three extended models, indicating that it would be difficult to establish which of them is best fit to describe the underlying new physics, should exotic leptons be detected. We suggest that, in order to resolve this difficulty, one should measure the angular distributions of single exotic leptons in longitudinally polarized {ital e}{sup +}{ital e}{sup {minus}} collisions.

Asymmetries in the littlest Higgs model

We discuss possible deviations from QED produced by a virtual excited spin-3/2 lepton in the reaction

Virtual bilepton effects in polarized Møller scattering

{e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}2\ensuremath{\gamma}.

On a \(Z^{\prime}\) signature at next high energy electron-positron colliders

Data recorded by the OPAL Collaboration at a c.m. energy