Sigma-assisted natural composite Higgs

Abstract

We show that the presence of a lightish scalar resonance, $\sigma$, that mixes with the composite Goldstone-Higgs boson can relax the typical bounds found in this class of models. This mechanism, inbred in models with a walking dynamics above the condensation scale, allows for a low compositeness scale $f\gtrsim 400$ GeV, corresponding to a misalignment angle $\sin \theta \lesssim 0.6$, contrary to the common lore of a smaller angle. According to recent lattice results, the light $\sigma$ emerges thanks to a near-conformal phase above the condensation scale, consistent to the requirements from flavour physics. We study this effect in a general way, showing that it appears in all cosets emerging from an underlying gauge-fermion dynamics, in the presence of top partial compositeness. The scenario is testable both on the Lattice and experimentally, as it requires the presence of a second broad Higgs-like resonance, below 1 TeV, that can be revealed at the LHC in the $ZZ$ and $t\bar{t}$ channels.

Comments: Extended version accepted for publication in EPJC. 16 pages, 7 figures (11 files)