If no Higgs then what?

TL;DR

This paper explores how adding a single spin-1 resonance can extend the Standard Model's validity without a Higgs boson, analyzing perturbative control, LHC phenomenology, and the impact of parity breaking.

Contribution

It identifies parameter regions where a minimal spin-1 triplet resonance maintains perturbative control and discusses its implications for LHC searches and electroweak symmetry breaking.

Findings

Elastic W/Z scattering suggests a high cutoff scale.

Including resonance scattering lowers the strong coupling onset.

Defined a self-consistent framework without unitarization schemes.

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 custodial SU(2) 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.