Article

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

ABSTRACT 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

Download full-text

Full-text

Available from: Elisabetta Furlan, Feb 06, 2015
0 Followers
 · 
108 Views
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: XQCAT (eXtra Quark Combined Analysis Tool) is a tool aimed to determine exclusion Confidence Levels (eCLs) for scenarios of new physics characterised by the presence of one or multiple heavy extra quarks (XQ) which interact through Yukawa couplings with any of the Standard Model (SM) quarks. The code uses a database of efficiencies for pre-simulated processes of Quantum Chromo-Dynamics (QCD) pair production and on-shell decays of extra quarks. In the version 1.0 of XQCAT the efficiencies have been computed for a set of seven publicly available search results by the CMS experiment, and the package is subject to future updates to include further searches by both ATLAS and CMS collaborations. The input for the code is a text file in which masses, branching ratios (BRs) and dominant chirality of the couplings of the new quarks are provided. The output of the code is the eCL of the test point for each implemented experimental analysis considered individually and, when possible, in statistical combination.