Related papers: Fourth-Generation Leptons at LEP2
The CERES/NA45 experiment at the CERN SPS has previously measured $e^{+}e^{-}$ pair production in 160 AGeV Pb-Au collisions. In the mass region m>0.2 GeV/c$^{2}$, an enhancement of $2.7\pm0.4(statist.)\pm0.5(syst.)$ compared to the…
The existence of extra chiral generations with all fermions heavier than M_Z is strongly disfavoured by the precision electroweak data. However the data are fitted nicely even by a few extra generations, if one allows neutral leptons to…
In the context of the future high energy - high luminosity electron and muon colliders, all the relevant four-lepton processes with the lepton family violation (LFV) are systematically classified. The most general LFV effective lagrangians…
It now appears phenomenologically that the third family of fundamental fermions may be essentially different fron the first two. Particularly the high value (174GeV?) of the top quark mass suggests a special role. In the standard model all…
We explore the possible implications that new families, that are being searched for at the LHC, would have on neutrino masses. In particular, we have explored the possibility that the smallness of the observed neutrino masses is naturally…
We have studied the radiative corrections from the fourth generation leptons in the context of the see-saw mechanism. We have estimated numerically the differential cross section for the process (${\rm e}^{+}{\rm e}^{-}\! \rightarrow {\rm…
Current mass limits for fourth generation sequential neutrinos come from dark matter experiments assuming $\rho_{DM}=0.2-0.8$ g/ cm$^3$. We show that the latest results from the CDMS II experiment exclude Dirac neutrinos with masses below…
A search for heavy neutral lepton production in $K^+$ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the $10^{-7}$ to $10^{-6}$ level are established on…
The necessity of the fourth family follows from the SM basics. According to flavor democracy the Dirac masses of the fourth SM family fermions are almost equal with preferable value 450 GeV, which corresponds to common (for all fundamental…
We investigate the newly observed muon $g_\mu -2$ anomaly in the framework of a sequential fourth generation model with a heavy fourth neutrino, $\nu'$. We find that $g_\mu -2$ can exclude most values of $m_{\nu'}$ and put a very stringent…
We point out the importance of two-body final states of weak isosinglet neutral heavy leptons predicted in several models of new physics beyond the standard model. We concentrate on muon-type neutral heavy leptons $L_\mu^0$ with mass $M<2$…
The very precise measurement of the anomalous magnetic moment of the muon, recently released by the Muon g-2 experiment at Fermilab, can serve to set stringent constraints on new particles. If the observed 4$\sigma$ discrepancy from the…
With one extra dimension, current high precision electroweak data constrain the masses of the first Kaluza-Klein excitations of the Standard Model gauge fields to lie above $\simeq 4$ TeV. States with masses not much larger than this should…
There has been renewed interest in the possibility of additional fermion generations. At the same time there have been significant changes in the relevant electroweak precision constraints, in particular, in the interpretation of several of…
We study 4D QED in which one spatial dimension is dynamically generated from 3D action, following the mechanism proposed by Arkani-Hamed, Cohen and Georgi. In this model, the generated fourth dimension is discretized by an interval…
Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 100pb-1 of e^+p data and 16pb-1 of e^-p data per experiment, taken in the years 1994-2000, the H1 and ZEUS collaborations have…
Leptogenic supersymmetry is a scenario characterized by cascade decays with copious lepton production. Leptogenic models have striking signatures that can be probed by the LHC even in the 10 TeV run with as little as 200 pb^-1 of data,…
Searches for New Particles including future sensitivity prospects are reviewed. The main focus is placed on results obtained at LEP, HERA and the Tevatron on generic searches such as searches for excited fermions, searches for leptoquarks…
In the minimal Standard Model (SM) with four generations (the so called SM4) and in "standard" two Higgs doublets model (2HDM) setups, e.g., the type II 2HDM with four fermion generations, the contribution of the 4th family heavy leptons to…
Single photons detected by the DELPHI experiment at LEP2 in the years 1997-2000 are reanalysed to investigate the existence of a single extra dimension in a modified ADD scenario with slightly warped large extra dimensions. The data…