Constraints from precision electroweak data on leptoquarks and bileptons

Abstract

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. Leptoquarks suggested by the neutral and charged current anomalies at HERA can give improved agreement with both S and T . If bileptons are the only new states, the singly-charged one must be heavier than the directlyestablished lower limit. Finally, we study SU (15) grand unification and show that there are regions of parameter space where the theory is compatible with experimental data.

Trilinear gauge boson couplings and bilepton production in the SU(3)C⊗SU(3)L⊗U(1)N models

“…One of the strongest limits on the bilepton mass comes from the fermion pair production and lepton-flavour violating charged lepton decays [22] at about 750 GeV. The current experimental lower limit on M X −− is claimed to be 850 GeV [30] (However, such a lower limit can be derived from oblique corrections assuming the Higgs mass to be equal to 300 GeV [21]). In this section, we present the cross sections for the production of two bileptons in both types of 3 -3 -1 models.…”

“…Adding the constraints from "wrong" muon decay experiments one also obtains a range for the new gauge charged bosons: M Y + ≥ 230 GeV. By computing the oblique parameters S and T , a lower bound of 367 GeV for the mass of the singly charged bilepton Y + is derived [21]. Combining this with the mass splitting given in (8) we obtain a lower bound around 400 GeV for the mass of the doubly charged bilepton (X ++ ).…”

Constraining the $$Z^{\prime }$$ Z ′ mass in 331 models using direct dark matter detection

“…In the latter setup the Z would be the mediator and therefore our bounds would apply up to some extent, because the couplings of the Z boson on those models are not so different from the model we investigate here. Moreover, these limits are complementary to other limits coming from colliders [37], Flavor Changing Neutral Current processes [38][39][40][41][42][43][44][45][46], electroweak corrections to the S,T,U parameters [47][48][49][50][51], and from muon decay [52,53]. More importantly, the limits on the mass of the Z found here imply a bound on the scale of symmetry breaking that forces all particle masses to lie at a few TeV, if one considers all couplings to be of order 1.…”

“…[37] do apply to our model. A variety limits have been placed on the mass of this boson and they come from different sources [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] and from different models. In summary, the bounds derived here on the mass of this boson are complementary to those.…”

The T 7 flavor symmetry in 3-3-1 model with neutral leptons

“…Our model contains a lot of SU(3) L scalar triplets that may modify the precision electroweak parameter such as S, T, U [188,189] and ρ parameters. The most serious one can result from the tree-level contributions to the ρ parameter.…”