Playing with fermion couplings in Higgsless models

Abstract

We discuss the fermion couplings in a four dimensional SU(2) linear moose model by allowing for direct couplings between the left-handed fermions on the boundary and the gauge fields in the internal sites. This is realized by means of a product of non linear $\sigma$-model scalar fields which, in the continuum limit, is equivalent to a Wilson line. The effect of these new non local couplings is a contribution to the $\epsilon_3$ parameter which can be of opposite sign with respect to the one coming from the gauge fields along the string. Therefore, with some fine tuning, it is possible to satisfy the constraints from the electroweak data.Comment: Latex file, 20 pages, 4 eps figure

Unitarity constraints on top quark signatures of Higgsless models

“…To give mass to the standard model (SM) fermions, we will additionally include two right-handed fermions χ bR and 1 Recently a similar construction for fermions delocalized over an arbitrary number of sites has been given [20] but the zero modes were treated as massless. Ref [19] uses another approach with localized fermions coupling nonlocally to the vector bosons. While this setup improves agreement with electroweak precision data, the unitarity issue is not addressed since no heavy partners for the top-and bottom quarks are introduced.…”

“…However, as pointed out subsequently [16,17] the delocalization of the fermions in the extra dimension or analogous theory space constructions [18][19][20] allows to suppress the couplings of the light fermions to the KK-gauge bosons and might be the key for a realistic model.…”

A Three Site Higgsless Model

“…Several authors proposed [27,28,29,30] that delocalizing fermions within the extra dimension could reduce electroweak corrections. In deconstructed language, delocalization means allowing fermions to derive electroweak properties from more than one site on the lattice of gauge groups [31,32]. We then showed [33] for an arbitrary Higgsless model that choosing the probability distribution of the delocalized fermions to be related to the wavefunction of the W boson makes three (Ŝ,T , W ) of the leading zero-momentum precision electroweak parameters defined by Barbieri, et. al.…”

Holographic approach to a minimal Higgsless model

“…These oblique corrections tend to give large and positive contributions to the ǫ 3 (or S) parameter, so that it is difficult to conciliate the electroweak bounds with a delay of the unitarity violation scale, [12,28]. However a delocalization of the fermionic fields into the bulk as in [32,33], that is allowing standard fermions with direct coupling to all the moose gauge fields as in [34], leads direct contributions to the electroweak parameters that can correct the bad behavior of the ǫ 3 parameter.…”