Realistic Composite Higgs Models

Physical review D: Particles and fields (Impact Factor: 4.86). 01/2009; 79(7). DOI: 10.1103/PhysRevD.79.075003
Source: arXiv


We study the role of fermionic resonances in realistic composite Higgs models. We consider the low energy effective description of a model in which the Higgs arises as the pseudo-Goldstone boson of an SO(5)/SO(4) global symmetry breaking pattern. Assuming that only fermionic resonances are present below the cut-off of our effective theory, we perform a detailed analysis of the electroweak constraints on such a model. This includes the exact one-loop calculation of the T parameter and the anomalous Zbb coupling for arbitrary new fermions and couplings. Other relevant observables, like b to s gamma and Delta B=2 processes have also been examined. We find that, while minimal models are difficult to make compatible with electroweak precision tests, models with several fermionic resonances, such as the ones that appear in the spectrum of viable composite Higgs models from warped extra dimensions, are fully realistic in a large region of parameter space. These fermionic resonances could be the first observable signature of the model at the LHC. Comment: 33 pages, 8 figures

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Available from: Elisabetta Furlan, Feb 06, 2015
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    • "Both CMS [18] and ATLAS [19] have recently devoted a considerable effort in the analyses apt to setting bounds on this type of new particles. Initially, simplifying assumptions were considered (mixing only with the third generation of SM quark family or specific decay modes) [20] [21] [22] [23] [24] [25] [26] [27] [28] [29]. However the most recent analyses, due to larger data samples, allow exploring more general situations with mixing – 1 – of VL quarks with the first two generation of SM quarks [30] [31] [32] [33] [34]. "
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    ABSTRACT: The ATLAS and CMS collaborations at the LHC have performed analyses on the existing data sets, studying the case of one vector-like fermion or multiplet coupling to the standard model Yukawa sector. In the near future, with more data available, these experimental collaborations will start to investigate more realistic cases. The presence of more than one extra vector-like multiplet is indeed a common situation in many extensions of the standard model. The interplay of these vector-like multiplet between precision electroweak bounds, flavour and collider phenomenology is a important question in view of establishing bounds or for the discovery of physics beyond the standard model. In this work we study the phenomenological consequences of the presence of two vector-like multiplets. We analyse the constraints on such scenarios from tree-level data and oblique corrections for the case of mixing to each of the SM generations. In the present work, we limit to scenarios with two top-like partners and no mixing in the down-sector.
    Full-text · Article · Feb 2015 · Journal of High Energy Physics
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    • "One can then include models with a pseudo- Nambu-Goldstone-Higgs [13] [14], general Composite Higgs Models (CHMs) [15], models of gauge-Higgs [16] and gauge coupling unification (see, e.g., [17] [18]) or extended custodial symmetry protecting the Zb ¯ b coupling from large deviations [19] [20]. After the discovery of the Higgs, most of the attention has been dedicated to XQs mixing exclusively with the top quark, in particular in the general scenario of a pseudo-Nambu-Goldstone (or Composite) Higgs state [21] [22] [23]. Finally, XQs coupled to the third generation of quarks have been thoroughly investigated from a phenomenological point of view [24] [25] [26] [27] [28], together with the possibility to have sizeable couplings to the light generations [29] [30]. "
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    ABSTRACT: In this paper we present an analysis strategy and a dedicated tool to determine the exclusion confidence level for any scenario involving multiple heavy extra quarks with generic decay channels, as predicted in several extensions of the Standard Model. We have created, validated and used a software package, called XQCAT (eXtra Quark Combined Analysis Tool), which is based on publicly available experimental data from direct searches for top partners and from Supersymmetry inspired searches. By means of this code, we recast the limits from CMS on new heavy extra quarks considering a complete set of decay channels. The resulting exclusion confidence levels are presented for some simple scenarios with multiple states and general coupling assumptions. Highlighting the importance of combining multiple topology searches to obtain accurate re-interpretations of the existing searches, we discuss the reach of the SUSY analyses so as to set bounds on new quark resonances. In particular, we report on the re-interpretation of the existing limits on benchmark scenarios with one and multiple pair-produced top partners having non-exclusive couplings to the third Standard Model generation of quarks.
    Preview · Article · Dec 2014 · Journal of High Energy Physics
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    • "The indirect constraints on the mixing parameters may be relaxed if several multiplets are present in the low-energy spectrum, as would be the case in realistic composite Higgs models [45]. Several authors have emphasized the importance of the single-production mechanism in this context [16] [45] [50], in particular, that it could represent a more favorable discovery mode than the pair-production mechanism. Figure 1(b) shows the predicted T ¯ bq cross section in a specific composite Higgs model [50] that was implemented in madgraph v5 [43] and provided by the authors of the model. "
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    ABSTRACT: A search is presented for the production of new heavy quarks that decay to a $Z$ boson and a third-generation Standard Model quark. In the case of a new charge +2/3 quark ($T$), the decay targeted is $T \rightarrow Zt$, while the decay targeted for a new charge -1/3 quark ($B$) is $B \rightarrow Zb$. The search is performed with a dataset corresponding to 20.3 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=8$ TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Selected events contain a high transverse momentum $Z$ boson candidate reconstructed from a pair of oppositely charged same-flavor leptons (electrons or muons), and are analyzed in two channels defined by the absence or presence of a third lepton. Hadronic jets, in particular those with properties consistent with the decay of a $b$-hadron, are also required to be present in selected events. Different requirements are made on the jet activity in the event in order to enhance the sensitivity to either heavy quark pair production mediated by the strong interaction, or single production mediated by the electroweak interaction. No significant excess of events above the Standard Model expectation is observed, and lower limits are derived on the mass of vector-like $T$ and $B$ quarks under various branching ratio hypotheses, as well as upper limits on the magnitude of electroweak coupling parameters.
    Preview · Article · Sep 2014 · Journal of High Energy Physics
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