Abstract
We present the first calculation of the scattering amplitude in the singlet channel beyond QCD. The calculation is performed in SU(2) gauge theory with N_f=2 fundamental Dirac fermions and based on a finite-volume scattering formalism. The theory exhibits a SU(4) rightarrow Sp(4) chiral symmetry breaking pattern that is used to design minimal composite Higgs models currently tested at the LHC. Our results show that, for the range of underlying fermion mass considered, the lowest flavour singlet state is stable.
Highlights
The discovery of the Standard Model’s (SM) last missing piece, the Higgs boson, and the increase in precision of tests of its properties, continue to trigger the study of numerous mechanisms to address the fundamental problems with its formulation.Among other possibilities, a new strongly interacting sector giving rise to the observed phenomenology at the electroweak scale (EW) and below has been pursued for decades
We report on the comparison of our results to the chiral perturbation theory predictions of Ref. [35], which should match in the limit of light enough pseudo-Nambu– Goldstone boson (PNGB)
This work represents the first study of the singlet channel in four-dimensional gauge theories beyond QCD
Summary
A new strongly interacting sector giving rise to the observed phenomenology at the electroweak scale (EW) and below has been pursued for decades Such a new sector could feature a solution to the naturalness problem and provide a mechanism to generate a non-trivial mass spectrum together with a large scale separation. These mechanisms have been used for instance in the context of Composite Higgs models [1–8], of scenarios of dynamical electroweak symmetry breaking [9–11], and of Dark Matter models [12,13]. The present work contributes to our understanding of the role of the σ resonance in the phenomenology of the class of composite models characterised by the strong sector we are considering, irrespectively of its embedding
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