Related papers: Once more on extra quark-lepton generations and pr…
Precise measurements of Z-boson parameters and W-boson and t-quark masses put strong constraints on non SU(2) * U(1) singlet New Physics. We demonstrate that one extra generation passes electroweak constraints even when all new particle…
The existence of extra chiral generations is strongly disfavored by the precision electroweak data if all the extra fermions are heavier than m_Z. However fits as good as the SM can be obtained if one allows the new neutral leptons to have…
The latest electroweak precision data are analyzed assuming the existence of the fourth generation of leptons ($N, E$) and quarks ($U, D$), which are not mixed with the known three generations. If all four new particles are heavier than $Z$…
The status of several precisely measured electroweak parameters is reviewed. Natural relations among them are shown to constrain the Higgs mass, m_H, as well as various ``New Physics'' effects. Indications of an anomalous Zb anti-b coupling…
It is shown that additional chiral generations are not excluded by the latest electroweak precision data if one assumes that there is no mixing with the known three generations. In the case of ``heavy extra generations'', when all four new…
The agreement of electroweak measurements with theory places limits on the masses of the top quark and the $W$ boson. It is shown how these limits arise and what constraints various measurements (particularly a top quark mass determination)…
We briefly review the limits on new interactions implied by electroweak precision data. Special attention is payed to the bounds on the Higgs boson mass. We also comment on the required cancellation among the new contributions to precisely…
We perform a global analysis of electroweak precision measurements to find constraints on physics beyond the Standard Model. In particular, we discuss oblique parameters, which are useful to constrain additional matter fields, as well as…
Our picture of the electroweak interactions continues to improve, with ever more precise constraints on the masses of the Higgs boson(s) and on non-standard physics. Some recent developments include: (a) a calculation of higher-order…
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…
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 effects of beyond the Standard Model physics coupling third generation quarks to leptons of the first two generations. We parametrize these effects by dimension-six effective operators, and we also consider related simplified UV…
We consider an extended electroweak gauge group: SU(2)$_1 \times$ SU(2)$_2 \times$ U(1)$_Y$ where the first and second generation of fermions couple to SU(2)$_1$ and the third generation couples to SU(2)$_2$. Bounds based on heavy gauge…
We study theoretical and experimental constraints on electroweak theories including a new color-singlet and electrically-neutral gauge boson. We first note that the electric charges of the observed fermions imply that any such Z' boson may…
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…
Explicit expressions are derived for the oblique parameters $S$ and $T$ in certain extensions of the standard model. In particular, we consider leptoquarks and bileptons, and find phenomenological constraints on their allowed masses.…
Electroweak Precision Measurements are stringent tests of the Standard Model and sensitive probes to New Physics. Accurate studies of the $Z$-boson couplings to the first-generation quarks, which are currently constrained from LEP data to a…
The link between the electroweak gauge boson masses and the Fermi constant via the muon lifetime measurement is instrumental for constraining and eventually pinning down new physics. We consider the simplest extension of the Standard Model…
We construct a new gauged $U(1)_\ell$ lepton number model which is anomaly-free for each SM generation. The active neutrino masses are radiatively generated with a minimal scalar sector. The phenomenology and collider signals are studied.…
We derive strong contraints on the Yukawa couplings and the vacuum expectation value in the singlet majoron model, taking into account the possibility of a small gravitationally induced mass for the majoron. If the present baryon asymmetry…