Related papers: Fourth-Generation Leptons at LEP2
We propose a simple extension of the standard model by adding a fourth generation vector-like lepton doublet and show that if the fourth neutrino is a massive pseudo-Dirac fermion with mass in the few hundred GeV range and mass splitting of…
In the energy region of LEP2 and above, four fermion final states in e+e- collisions can be produced by Feynman diagrams involving two, one or zero resonant bosons...
We derive the low-energy electroweak effective lagrangian for the case of additional heavy, unmixed, sequential fermions. Present data still allow for the presence of a new quark and/or lepton doublet with masses greater than $M_Z/2$,…
The first evidence of new strong interactions may be a sufficiently massive fourth family observed at the LHC. The fourth family masses, of the leptons in particular, are constrained by the electroweak precision data, and this leads to…
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…
The measurements of four-fermion production rates performed at LEP2 in e+e- collisions at centre-of-mass energies ranging from 161 to 209 GeV are presented. The focus is put on processes that involve the production and decay of W or Z…
For the first time at LEP most of the events will have four fermions in the finals state and we have the unique opportunity of testing a complete calculation with the experimental data, well beyond the usual approximation of computing…
We report the most restrictive direct limits on masses of fourth-generation down-type quarks $b^{\prime}$, and quark-like composite fermions ($B$ or $T_{5/3}$), decaying promptly to $t W^{\mp}$. We search for a significant excess of events…
I discuss the production of leptoquarks in $p\bar{p}$ collisions at the Fermilab Tevatron. Evaluated on the basis of a recent next-to-leading order calculation, the combined D0 and CDF leptoquark searches lead to a parameter-free lower mass…
A search for first and second generation leptoquarks has been done with the D\O \ detector at Fermilab's p\={p} collider with $\sqrt{s}=1.8$ TeV. 95\% C.L. mass limits for first generation scalar leptoquarks have been recently published.…
We consider the bounds for the values of higgs mass $m_H$ and the mass of the extra quarks and leptons $m_{extra}$ derived from the stability of electroweak vacuum and from the absence of Landau pole in Higgs potential. We find that in the…
The NA48/2 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2003--2004. A new upper limit on the rate of the lepton number violating decay…
Preliminary results on $e^+ e^- \to f \bar{f}$, $f=e, \mu, \tau, q$, including all LEP2 data are discussed. Good agreement is found with the Standard Model up to the highest energies. Limits on possible new physics are extracted.
We propose $S_4$ symmetric four-generation models for charged leptons. Although an $S_4$ symmetric four-generation model has been already proposed, there are some additional symmetries in the model. We construct four-generation models for…
It is possible that there are additional vector-like generations where the quarks have mass terms that do not originate from weak symmetry breaking, but the leptons only get mass through weak symmetry breaking. We discuss the impact that…
Very little is known about the mass spectrum of fermions in the standard model. In this talk, I point out that in the simplest extension of the standard model, in which all right-handed fields are singlets, it is quite possible that a…
A search for pair production of second-generation leptoquarks is performed using proton-proton collision data collected at $\sqrt{s}=$ 13 TeV in 2016 with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 35.9…
The existence of the fourth quark-lepton generation is not excluded by the electroweak precision data. However, the recent results on the 126 GeV higgs boson production and decay do not allow an extra generation at least as far as the…
A sequential fourth generation of quarks and leptons is allowed by precision electroweak constraints if the mass splitting between the heavy quarks is between 50 and 80 GeV. Although heavy quarks can be easily detected at the LHC, it is…
We use sampling techniques to find robust constraints on the masses of a possible fourth sequential fermion generation from electroweak oblique variables. We find that in the case of a light (115 GeV) Higgs from a single electroweak…