Properties of a composite Higgs particle in a dynamically broken formulation of the standard model

Abstract

We suggest that dynamical breakdown of electroweak symmetry in an SU(3)xSU(2)xU(l) model of a single fermion family without fundamental scalars can reproduce the entire scalar sector of the standard model through fermion bound states and loop-induced couplings. The physical Higgs boson is essentially a it bound state. The top-quark and Higgs-boson masses are approximately 300 and 400 GeV, respectively. The strengths of the induced couplings among the scalars do not indicate a strongly interacting scalar sector.All experimental indications are that the standard model (SM) provides an adequate description of strong and electroweak interactions at all energy scales explored to date. Not every aspect of the SM has been tested, however. Perhaps the most crucial untested feature is the mechanism responsible for the spontaneous breakdown of electroweak symmetry. A key step toward verification of the SM would be the discovery of the physical Higgs boson (//), the one directly observable particle of the four fundamental scalars introduced into the theory to explain symmetry breaking.Should something resembling the H be discovered, however, it will have to be studied closely to determine whether it is indeed a fundamental particle. A composite H could well exist if the symmetry breaking is driven by a dynamical mechanism, rather than by fundamental scalars as in the SM. In models employing dynamical symmetry breaking (DSB), 1 the massless Goldstone states that become the longitudinal components of the W -and Z bosons are generally assumed to be fermionantifermion composites; conceivably the same dynamics that produces these composites could generate one or more composite //'s as well.In this Letter we discuss the properties of a composite Higgs boson that appears to exist in a particular electroweak model incorporating DSB. We argue that the couplings of the composite H to all other particles, when evaluated to a first approximation, are identical to the corresponding tree-level couplings of the fundamental H in the SM. Thus a composite H of this type would be very difficult to distinguish from a fundamental H.The model we consider 2 is based on the SU(3) xSU(2)xU(l) Lagrangian of the SM, minus all terms involving scalar fields. Note that omitting all reference to scalars means omitting all Yukawa couplings and scalar potential parameters. Thus, this model has fewer free parameters than the SM and, potentially, greater predictive power.We restrict our discussion to a one-family model in order to avoid complications that arise in the multifamily case, 2,3 but that are not relevant to the present discussion. As will become clear below, in order to make contact with experiment we should identify this single family with the third family (t,b,r, v r ).Unlike more conventional DSB models, particularly those based on the technicolor idea, 4 our model contains no QCD-like strong interaction at the TeV scale to which electroweak symmetry breaking is ascribed. We nevertheless assume that the symmetry-breaking selfenergies are of the...

Light composite Higgs from an effective action for technicolor

“…1, and the extreme walking technicolor solution obtained when ! 0 [6], i.e., this is the case where the symmetry breaking is dominated by higher order interactions that are relevant at or above the TC scale, leading naturally to a very hard dynamics [16,17]. As two of us have pointed out in Ref.…”

Fourth generation Majorana neutrinos

“…(iii) If problems with arising Landau poles can be cured, the SM4 might also help to achieve a unification of couplings [26]. (iv) Large Yukawa couplings might lead to new, interesting, strong dynamic effects [27,28] including dynamical symmetry breaking [29][30][31][32][33][34][35][36][37][38][39][40][41]. (v) Despite the enormous success of the Cabibbo-Kobayashi-Maskawa picture [42,43], the assumption that both B d and B s mixing are described by the SM3 alone is excluded by 3.8 standard deviations [44].…”

Electroweak Theory Without Higgs Bosons

“…And our scheme is perturbative in the gauge coupling. This feature differs from the non-perturbative "soft" fermion self-energy ansatz for dynamically breaking chiral gauge symmetries discovered by Jackiw and Johnson [34] and applied to the Standard Model by Carpenter et al [35]. In that scenario, the gauge boson and fermion mass(es) are linked by a finite relationship after renormalisation that predicts too large a top quark mass (or equivalently, too small W and Z masses).…”

“…whereπ AN L , independent of k 2 and real, is defined by (25) with J = A, while c A is determined, by (9), from c W , c Z given by (35); it is of the form of c J , (24). To one loop, (55), (63) below show that ρ A (k 2 ) = 0 and thatπ A diverges.…”