Dirac and Majorana heavy neutrinos at LEP II

The possibility of detecting single heavy Dirac and Majorana neutrinos at LEP II is investigated for heavy neutrino masses in the range $M_N=(\sqrt s/2, \sqrt s)$. We study the process $e^+e^- \longrightarrow \nu_{\ell} \ell q_i \bar q_j$ as a clear signature for heavy neutrinos. Numerical estimates for cross sections and distributions for the signal and the background are calculated and a Monte Carlo reconstruction of final state particles after hadronization is presented.Comment: 4 pages, 8 figure

Discriminating among the theoretical origins of new heavy Majorana neutrinos at the 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 non-zero 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.Comment: 7 pages, 5 figure

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

The associated production of a $Z^{\prime}$ and a final hard photon in high energy electron-positron colliders is studied. It is shown that the hard photon spectrum contains useful information on the $Z^{\prime}$ properties. This remark suggests that, if a new neutral gauge boson exists for $M_{Z^{\prime}} < \sqrt{s}$, it will not be necessary to make a new energy run at the $Z^{\prime}$ mass in order to get most of its properties.Comment: 10 pages and 7 figure

Asymmetries in the Littlest Higgs Model

Little Higgs models were recently proposed as an alternative for models of electroweak symmetry breaking. They can be regarded as one of the important candidates of the new physics beyond the Standard Model. We consider here the phenomenology of the minimal model of this type, the &quot;Littlest Higgs Model&quot; (LHM). It predicts the existence of the new gauge bosons Z H and A H . We calculate the contributions of these new particles to the forward-backward and left-right asymmetries in the processes e + +e − −→ f +f . We study the possibility of detecting the lightest new gauge boson, A H , in the future e+e-colliders with c.m. energies of 500 GeV and 1 TeV and compare the LHM predictions with other models