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Register a new userPhenomenology of a Composite Higgs Model
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Several UV complete models of physics beyond the Standard Model are currently under scrutiny, their low-energy dynamics being compared with the experimental data from the LHC. Lattice simulations can play a role in these studies by providing a first principles computations of the low-energy constants that describe this low-energy dynamics. In this work, we study in detail a specific model recently proposed by Ferretti, and discuss the potential impact of lattice calculations.
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Experimentally the existence of a light 125 GeV Higgs boson is well established but so far no other heavier resonances have been observed. Viable models to describe the Higgs boson as composite particle require hence to exhibit a large separation of scales. This occurs naturally in systems located near a conformal fixed point irrespective whether the system lies outside or inside the conformal window. We demonstrate the latter case by investigating a mass-split model with four light and six heavy flavors. By construction mass-split models exhibit a large separation of scales and feature in addition a highly constrained hadron spectrum. We present results based on the low-lying connected meson spectrum. Although the light sector is chirally broken, we show that it exhibits hyperscaling which is typical for conformal systems.
We study the phenomenology of partially composite-Higgs models where electroweak symmetry breaking is dynamically induced, and the Higgs is a mixture of a composite and an elementary state. The models considered have explicit realizations in terms of gauge-Yukawa theories with new strongly interacting fermions coupled to elementary scalars and allow for a very SM-like Higgs state. We study constraints on their parameter spaces from vacuum stability and perturbativity as well as from LHC results and find that requiring vacuum stability up to the compositeness scale already imposes relevant constraints. A small part of parameter space around the classically conformal limit is stable up to the Planck scale. This is however already strongly disfavored by LHC results. In different limits, the models realize both (partially) composite-Higgs and (bosonic) technicolor models and a dynamical extension of the fundamental Goldstone-Higgs model. Therefore, they provide a general framework for exploring the phenomenology of composite dynamics.
Twin Higgs models are economical extensions of the Standard Model that stabilize the electroweak scale. In these theories the Higgs field is a pseudo Nambu-Goldstone boson that is protected against radiative corrections up to scales of order 5 TeV by a discrete parity symmetry. We construct, for the first time, a class of composite twin Higgs models based on confining QCD-like dynamics. These theories naturally incoporate a custodial isospin symmetry and predict a rich spectrum of particles with masses of order a TeV that will be accessible at the LHC.
We analyze three sets of gauge ensembles in our extended physics program of a particularly important BSM gauge theory with a fermion doublet in the two-index symmetric (sextet) representation of the SU(3) BSM color gauge group. Our investigations include chiral symmetry breaking $rm{(chi SB)}$ in the p-regime and $epsilon$-regime, the mass of the composite ${rm 0^{++}}$ scalar, resonance spectroscopy, new physics from gauge anomaly constraints, and the role of stable sextet BSM baryons with Electroweak interactions in dark matter searches. Important new goals include studies of the ${rm 0^{++}}$ scalar entangled with Goldstone dynamics in the p-regime and the $epsilon$-regime, the resonance spectrum with particular attention to emerging LHC signals, like recent hints for diphoton excess at 750 GeV or diboson anomalies in the 2 TeV range. All results reported here are preliminary before journal publication including some post-conference material for the discussion.
We propose to construct a chirally broken model based on the infrared fixed point of a conformal system by raising the mass of some flavors while keeping the others massless. In the infrared limit the massive fermions decouple and the massless fermions break chiral symmetry. The running coupling of this system walks and the energy range of walking can be tuned by the mass of the heavy flavors. Renormalization group considerations predict that the spectrum of such a system shows hyperscaling. We have studied a model with four light and eight heavy flavors coupled to SU(3) gauge fields and verified the above expectations. We determined the mass of several hadronic states and found that some of them are in the 2-3 TeV range if the scale is set by the pseudoscalar decay constant $F_pi approx 250$ GeV. The $0^{++}$ scalar state behaves very differently from the other hadronic states. In most of our simulations it is nearly degenerate with the pion and we estimate its mass to be less than half of the vector resonance mass.
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