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Register a new userA UV complete partially composite-pNGB Higgs
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We explore an electroweak symmetry breaking (EWSB) scenario based on the mixture of a fundamental Higgs doublet and an SU(4)/Sp(4) composite pseudo-Nambu-Goldstone doublet -- a particular manifestation of bosonic technicolor/induced EWSB. Taking the fundamental Higgs mass parameter to be positive, EWSB is triggered by the mixing of the doublets. This setup has several attractive features and phenomenological consequences, which we highlight: i) Unlike traditional bosonic technicolor models, the hierarchy between $Lambda_{rm TC}$ and the electroweak scale depends on vacuum (mis)alignment and can be sizable, yielding an attractive framework for natural EWSB; ii) As the strong sector is based on SU(4)/Sp(4), a fundamental (UV-complete) description of the strong sector is possible, that is informed by the lattice; iii) The lightest vector resonances occur in the 10-plet, 5-plet and singlet of Sp(4). Misalignment leads to a 10-plet parity-doubling cancelation in the $S$ parameter, and a suppressed 5-plet contribution; iv) Higgs coupling deviations are typically of $mathcal O(1%)$; v) The 10-plet isotriplet resonances decay dominantly to a massive technipion and a gauge boson, or to technipion pairs, rather than to gauge boson or fermion pairs; moreover, their couplings to fermions are small. Thus, the bounds on this setup from conventional heavy-vector-triplet searches are weak. A supersymmetric $U(1)_R$ symmetric realization is briefly described.
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One of the most challenging hurdles to the construction of realistic composite Higgs models is the generation of Yukawa couplings for the Standard Model fermions. This problem can be successfully addressed in approximate conformal theories that admit a marginally relevant mixing between composite fermionic operators and the SM fermions. I argue that SU(3) gauge theories with light Dirac flavors in the fundamental representation feature all the ingredients under theoretical control, including a strongly-coupled IR fixed point, composite partners for all Standard Model fermions, absence of Landau poles at low energy, and a realistic phenomenology. These models acquire the status of compelling UV-completions of the SM if some spin-1/2 baryon operator has scaling dimension close to 2.5 within the conformal window, a possibility that can only be assessed via non-perturbative methods like lattice QCD. A distinctive collider signature is long-lived hadrons with fractional charges. Vacuum alignment is controlled by the Nambu-Goldstone bosons of the coset SU(4)xSU(4)/SU(4). With a technically natural choice of mixing for the top-quark, the exotic scalars with electro-weak charges acquire large positive masses and a compelling custodial-symmetric phenomenology is obtained. In the decoupling limit the symmetry breaking pattern effectively reduces to SU(4)->Sp(4) with a light Higgs.
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.
We consider a supersymmetric model that uses partial compositeness to explain the fermion mass hierarchy and predict the sfermion mass spectrum. The Higgs and third-generation matter superfields are elementary, while the first two matter generations are composite. Linear mixing between elementary superfields and supersymmetric operators with large anomalous dimensions is responsible for simultaneously generating the fermion and sfermion mass hierarchies. After supersymmetry is broken by the strong dynamics, partial compositeness causes the first- and second-generation sfermions to be split from the much lighter gauginos and third-generation sfermions. This occurs even though the tree-level soft masses of the elementary fields are subject to large radiative corrections from the composite sector, which we calculate in the gravitational dual theory using the AdS/CFT correspondence. The sfermion mass scale is constrained by the observed 125 GeV Higgs boson, leading to stop masses and gauginos around 10-100 TeV and the first two generation sfermion masses around 100-1000 TeV. This gives rise to a splitlike supersymmetric model that explains the fermion mass hierarchy while simultaneously predicting an inverted sfermion mass spectrum consistent with LHC and flavor constraints. Finally, the lightest supersymmetric particle is a gravitino in the keV to TeV range, which can play the role of dark matter.
We consider the strong dynamics associated with a composite Higgs model that simultaneously produces dynamical axions and solves the strong CP problem. The strong dynamics arises from a new $Sp$ or $SU(4)$ hypercolor gauge group containing QCD colored hyperfermions that confines at a high scale. The hypercolor global symmetry is weakly gauged by the Standard Model electroweak gauge group and an enlarged color group, $SU(N+3) times SU(N)$. When hyperfermion condensates form, they not only lead to an $SU(5)/SO(5)$ composite Higgs model but also spontaneously break the enlarged color group to $SU(3)_c times SU(N)_D$. At lower energies, the $SU(N)_D$ group confines, producing two dynamical axions that eliminates all CP violation. Furthermore, small instantons from the $SU(N)$ group can enhance the axion mass, giving rise to TeV scale axion masses that can be detected at collider experiments. Our model provides a way to unify the composite Higgs with dynamical axions, without introducing new elementary scalar fields, while also extending the range of axion masses that addresses the strong CP problem.
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.
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