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Register a new userBoosting Top Partner Searches in Composite Higgs Models
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Fermionic third generation top partners are generic in composite Higgs models. They are likely to decay into third generation quarks and electroweak bosons. We propose a novel cut-and-count-style analysis in which we cross correlate the model-dependent single and model-independent pair production processes for the top partners $X_{5/3}$ and $B$. In the class of composite Higgs models we study, $X_{5/3}$ is very special as it is the lightest exotic fermion. A constraint on the mass of $X_{5/3}$ directly extends to constrains on all top partner masses. By combining jet substructure methods with conventional reconstruction techniques we show that in this kind of final state a smooth interpolation between the boosted and unboosted regime is possible. We find that a reinterpretation of existing searches can improve bounds on the parameter space of composite Higgs models. Further, at 8 TeV a combined search for $X_{5/3}$ and $B$ in the $l+rm{jets}$ final state can be more sensitive than a search involving same-sign dileptons.
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We consider composite two-Higgs doublet models based on gauge-Yukawa theories with strongly interacting fermions generating the top-bottom mass hierarchy. The model features a single universal Higgs-Yukawa coupling, $ g $, which is identified with the top quark $ gequiv g_t sim mathcal{O}(1) $. The top-bottom mass hierarchy arises by soft breaking of a $ mathbb{Z}_2 $ symmetry by a condensate of strongly interacting fermions. A mass splitting between vector-like masses of the confined techni-fermions controls this top-bottom mass hierarchy. This mechanism can be present in a variety of models based on vacuum misalignment. For concreteness, we demonstrate it in a composite two-Higgs scheme.
We consider how best to search for top partners in generic composite Higgs models. We begin by classifying the possible group representations carried by top partners in models with and without a custodial $SU(2)times SU(2) rtimes mathbb{Z}_2$ symmetry protecting the rate for $Z rightarrow boverline{b}$ decays. We identify a number of minimal models whose top partners only have electric charges of $frac{1}{3}, frac{2}{3},$ or $frac{4}{3}$ and thus decay to top or bottom quarks via a single Higgs or electroweak gauge boson. We develop an inclusive search for these based on a top veto, which we find to be more effective than existing searches. Less minimal models feature light states that can be sought in final states with like-sign leptons and so we find that 2 straightforward LHC searches give a reasonable coverage of the gamut of composite Higgs models.
We provide gauge/gravity dual descriptions of the strong coupling sector of composite Higgs models using insights from non-conformal examples of the AdS/CFT correspondence. We calculate particle masses and decay constants for proposed Sp(4) and SU(4) gauge theories, where there is the best lattice data for comparison. Our results compare favorably to lattice studies and go beyond those due to a greater flexibility in choosing the fermion content. That content changes the running dynamics and its choice can lead to sizable changes in the bound state masses. We describe top partners by a dual fermionic field in the bulk. Including suitable higher dimension operators can ensure a top mass consistent with the standard model.
We study Higgs couplings in the composite Higgs model based on the coset SO(5)/SO(4). We show that the couplings to gluons and photons are insensitive to the elementary-composite mixings and thus not affected by light fermionic resonances. Moreover, at leading order in the mixings the Higgs couplings to tops and gluons, when normalized to the Standard Model (SM), are equal. These properties are shown to be direct consequences of the Goldstone symmetry and of the assumption of partial compositeness. In particular, they are independent of the details of the elementary-composite couplings and, under the further assumption of CP invariance, they are also insensitive to derivative interactions of the Higgs with the composite resonances. We support our conclusions with an explicit construction where the SM fermions are embedded in the 14 dimensional representation of SO(5).
We consider a composite Higgs model based on the $SU(6)/Sp(6)$ coset, where an $U(1)$ subgroup of $Sp(6)$ is identified as the flavor symmetry. A complex scalar field $s$, which is a pseudo-Nambu-Goldstone boson of the broken symmetry, carries a flavor charge and plays the role of a flavon field. The $U(1)_F$ flavor symmetry is then broken by a VEV of the flavon field, which leads to a small parameter and generates the mass hierarchy between the top and bottom quarks. A light flavon below the TeV scale can be naturally introduced, which provides a fully testable model for the origin of flavor hierarchy. A light flavon also leads to substantial flavor changing neutral currents, which are strongly constrained by the flavor precision tests. The direct search of additional scalar bosons can also be conducted in HL-LHC and future hadron colliders.
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