The Strongly-Interacting Light Higgs

TL;DR

The paper develops the Strongly-Interacting Light Higgs (SILH) framework, characterizing a light composite Higgs as a pseudo-Goldstone from a strong sector via two main parameters, m_rho and g_rho, and presents a model-independent EFT below m_rho. It derives the SILH effective Lagrangian with dimension-6 operators, classifies them into those testing the strong dynamics versus those sensitive to the resonance spectrum, and connects them to explicit UV completions like holographic Higgs and Little Higgs models. The phenomenology focuses on Higgs and longitudinal gauge-boson processes, predicting energy-growing V_LV_L scattering, modified Higgs couplings through c_H and c_y, and potential top compositeness, with complementary tests from triple gauge couplings and direct resonance searches. The framework provides a robust, testable approach for probing strong electroweak breaking at the LHC and ILC, including flavor implications if the top is composite.

Abstract

We develop a simple description of models where electroweak symmetry breaking is triggered by a light composite Higgs, which emerges from a strongly-interacting sector as a pseudo-Goldstone boson. Two parameters broadly characterize these models: m_rho, the mass scale of the new resonances and g_rho, their coupling. An effective low-energy Lagrangian approach proves to be useful for LHC and ILC phenomenology below the scale m_rho. We identify two classes of operators: those that are genuinely sensitive to the new strong force and those that are sensitive to the spectrum of the resonances only. Phenomenological prospects for the LHC and the ILC include the study of high-energy longitudinal vector boson scattering, strong double-Higgs production and anomalous Higgs couplings. We finally discuss the possibility that the top quark could also be a composite object of the strong sector.

Figures (1)

• Figure 1: The deviations from the SM predictions of Higgs production cross sections ($\sigma$) and decay branching ratios ($BR$) defined as $\Delta (\sigma ~BR)/(\sigma ~BR)=(\sigma ~BR)_{\rm SILH}/(\sigma ~BR)_{\rm SM} -1$. The predictions are shown for some of the main Higgs discovery channels at the LHC with production via vector-boson fusion (VBF), gluon fusion ($h$), and topstrahlung ($tth$). The SILH Lagrangian parameters are set by $c_H\xi =1/4$, $c_y/c_H=1$ and we have included also the terms quadratic in $\xi$, not explicitly shown in eqs. (\ref{['gam1']})--(\ref{['gam6']}).