If no Higgs then what?

Abstract

In the absence of a Higgs boson, the perturbative description of the Standard Model ceases to make sense above a TeV. Heavy spin-1 fields coupled to W and Z bosons can extend the validity of the theory up to higher scales. We carefully identify regions of parameter space where a minimal addition -a single spin-1 SU(2) custodial -triplet resonance -allows one to retain perturbative control in all channels. Elastic scattering of longitudinal W and Z bosons alone seems to permit a very large cut-off beyond the Naive Dimensional Analysis expectation. We find however that including scattering of the spin-1 resonances then leads to an earlier onset of strong coupling. Most importantly for LHC searches, we define a self-consistent set-up with a well-defined range of validity without recourse to unitarization schemes whose physical meaning is obscure. We discuss the LHC phenomenology and the discovery reach for these electroweak resonances and mention the possibility of a nightmare scenario with no Higgs nor resonance within the LHC reach. Finally, we discuss the effects of parity breaking in the heavy resonance sector which reduces the contributions to the S parameter.

Exploring T and S parameters in Vector Meson Dominance models of strong electroweak symmetry breaking

“…4 See [25] for a recent discussion of strong EWSB without parity. The SM gauge group partly gauges the global symmetry of the EWSB sector.…”

“…6 A disadvantage of the antisymmetric tensor formalism is that the current automated collider physics tools do not deal with antisymmetric tensors. For this reason collider studies of Higgsless models are usually performed in the other two formalisms [25,28]. 7 Axial spin-1 states can be introduced via the 4-site model [31][32][33].…”

“…Eventually, unitarity is violated by the logarithmically growing terms in a 0 0 (s). However, even before this, opening of inelastic channels like ππ → V V has to be taken into account [25,28,39]. Because of this, we will trust the amplitude (3.10) and the resulting partial unitarity restoration at most up to ∼ 2M V .…”

Probing strongly interacting W’s at the ILC with polarized beams

“…In these cases, gauge bosons become strongly interacting after crossing the light Higgs resonance. Thus, even with the discovery of a light scalar particle in the small window available at the LHC [7,8], a detailed analysis of the gauge boson interactions, especially probing the signatures of their strong interactions in processes with W and/or Z bosons in the final state is essential to understand the mechanism of EWSB, as emphasised by [34,35]. Phenomenology of such models at LHC are considered in ref.…”

“…The ultraviolet completion of such effective theories are expected to explain the origin of such resonances. In most cases, it is argued [28,34], that the vector bosons are the dominant resonances. Among the renomarlizable theories explaining the origin of vector resonances , the idea of dynamical EWSB of technicolour models [39] proposing a composite scalar sector with a techni-ρ meson playing the role of the vector resonance mentioned above has been studied in detail in the past decades.…”