Minimal composite Higgs models at the LHC

We perform a Bayesian statistical analysis of the constraints on the nonlinear Effective Theory given by the Higgs electroweak chiral Lagrangian. We obtain bounds on the effective coefficients entering in Higgs observables at the leading order, using all available Higgs-boson signal strengths from the LHC runs 1 and 2. Using a prior dependence study of the solutions, we discuss the results within the context of natural-sized Wilson coefficients. We further study the expected sensitivities to the different Wilson coefficients at various possible future colliders. Finally, we interpret our results in terms of some minimal composite Higgs models.

Section: The Higgs Electroweak Chiral Lagrangianmentioning

confidence: 99%

Current and future constraints on Higgs couplings in the nonlinear Effective Theory

Blas

Eberhardt

Krause

2018

“…One reason is that, in the strictly IR approach, one has no control over the possible group realizations, (both the coset and the irreps) of the theory and one is forced to guess or to scan over "group theory space" (see e.g. [32,33]). The UV completion can help pointing towards the most promising models.…”

Section: Jhep06(2014)142mentioning

confidence: 99%

UV completions of partial compositeness: the case for a SU(4) gauge group

Ferretti

2014

139

253

We present a model of partial compositeness arising as the IR limit of a SU(4) gauge theory with only fermionic matter. This group is one of the most promising ones among a handful of possible choices allowing a symmetry breaking pattern incorporating custodial symmetry and a top partner candidate, while retaining asymptotic freedom. It is favored for not giving rise to lepto-quarks or Landau poles in the SM gauge couplings. The minimal UV theory consists of five hyperfermions in the anti-symmetric representation and three in the fundamental and anti-fundamental. The IR theory is centered around the coset SU(5)/SO(5), with top partners in the fundamental of SO(5), giving rise to one composite fermion of electric charge 5/3, three of charge 2/3 and one of charge −1/3. Electro-Weak symmetry breaking occurs via top-quark-driven vacuum misalignment. The top quark mass is generated via the mechanism of partial compositeness, while the remaining fermions acquire a mass via a standard quadratic coupling to the Higgs. We compute the top and bottom quark mass matrix and the Electro-Weak currents of the composite fermions. The model does not give rise to unacceptably large deviations from the SM Z → bb decay width.

“…The interactions of the pNGBs are determined by low energy theorems, and hence the only remaining task is to specify the form of the interactions between the SM fermions and the composite sector, which boils down to choosing the precise embeddings of the elementary fermions in representations of SO (5). In this paper, we focus on the two-site 4D models that were previously described in [18,34,35]. The mechanics of the collective breaking will be broadly summarised below.…”

Section: Jhep09(2017)049mentioning

confidence: 99%

“…The gauge sector is common to each of our theories, and is unchanged from [22,35]. An angle t θ ≡ tan θ, assumed to be small, quantifies the amount of mixing between the elementary and composite sectors, whilst the masses of the two lightest vector resonances are given by m ρ and m a .…”

Section: Details Of the Gauge Sectormentioning

confidence: 99%

“…Each representation's form factors generally depend on the four following functions: The precise expressions for the source terms in this study are slightly different from both [22,35], so we present them in full for each representation. The expressions for the SO(4) decomposed form factors are to be found originally in [35]. They are included here for completeness.…”

Section: A Fermion Representation Expressionsmentioning

confidence: 99%

See 1 more Smart Citation

Constraining fine tuning in composite Higgs models with partially composite leptons

Barnard

Murnane

Williams

2017

Minimal Composite Higgs Models (MCHM) have long provided a solution to the hierarchy problem of the Standard Model, yet suffer from various sources of fine tuning that are becoming increasingly problematic with the lack of new physics observations at the LHC. We develop a new fine tuning measure that accurately counts each contribution to fine tuning (single, double, triple, etc) that can occur in a theory with n p parameters, that must reproduce n o observables. We then use a novel scanning procedure to perform a comprehensive study of three different two-site, 4D, SO(5) → SO(4) MCHMs with all third generation fermions included, distinguished by the choice of the lepton embeddings. These are the MCHM 5-5-5 5-5-5 , MCHM 5-5-5 14-14-10 and MCHM 5-5-5 14-1-10 , where MCHM q−t−b l−τ −ν has the lepton doublet partner in representation l, tau partner in representation τ , and so on. We find that embedding at least one massive lepton in the symmetric 14 of SO (5) moderately reduces the tuning for the case of low top partner masses (in line with previous results), but that this is balanced against the increased complexity of the model when one properly accounts for all sources of fine tuning. We study both the current relative fine-tuning of each scenario, and the future prospects. Noting that the different scenarios behave differently with respect to future improvements in collider measurements, we find that the MCHM 5-5-5 14-1-10 enjoys a relatively low increase in fine tuning even for a future lower bound on the top partner masses of 3.4 TeV (or equivalently a maximum Higgs-fermion or Higgs-gluon coupling deviation of 2%).