Kingman Cheung

Top quark forward–backward asymmetry

Abstract The recent forward–backward asymmetry recorded by the CDF Collaboration for the top and anti-top quark pair production indicates more than 2 σ deviation from the Standard Model prediction, while its total production cross section remains consistent. We propose a W ′ boson that couples to down and top quarks. We identify the parameter space that can give rise a large enough forward–backward asymmetry without producing too many top and anti-top quark pairs. Other models presented previously in the literature that can produce such effects are also briefly discussed.

Higgs precision (Higgcision) era begins

A bstractAfter the discovery of the Higgs boson at the LHC, it is natural to start the research program on the precision study of the Higgs-boson couplings to various standard model (SM) particles. We provide a generic framework for the deviations of the couplings from their SM values by introducing a number of parameters. We show that a large number of models beyond the SM can be covered, including two-Higgs-doublet models, supersymmetric models, little-Higgs models, extended Higgs sectors with singlets, and fourth generation models. We perform global fits to the most updated data from CMS, ATLAS, and Tevatron under various initial conditions of the parameter set. In particular, we have made explicit comparisons between the fitting results before and after the Moriond 2013 meetings. Highlights of the results include: (i) the nonstandard decay branching ratio of the Higgs boson is less than 22%; (ii) the most efficient way to achieve the best fit for the data before the Moriond update is to introduce additional particle contributions to the triangular-loop functions of Hγγ and Hgg vertices; (iii) the 1σ allowed range of the relative coupling of HVV is

Global constraints on effective dark matter interactions: relic density, direct detection, indirect detection, and collider

1.01_{-0.14}^{+0.13 }

Global Study of the Simplest Scalar Phantom Dark Matter Model

, which means that the electroweak-symmetry breaking contribution from the observed Higgs boson leaves only a small room for other Higgs bosons; (iv) the current data do not rule out pseudoscalar couplings nor pseudoscalar contributions to the Hγγ and Hgg vertices; and (v) the SM Higgs boson provides the best fit to all the current Higgs data.

Higgs precision study of the 750 GeV diphoton resonance and the 125 GeV standard model Higgs boson with Higgs-singlet mixing

An effective interaction approach is used to describe the interactions between the spin 0 or spin 1/2 dark matter particle and the degrees of freedom of the standard model. This approach is applicable to those models in which the dark matter particles do not experience the standard-model interactions, e.g., hidden-sector models. We explore the effects of these effective interaction operators on (i) dark matter relic density, (ii) spin-independent and spin-dependent dark matter-nucleon scattering cross sections, (iii) cosmic antiproton and gamma ray fluxes from the galactic halo due to dark matter annihilation, and (iv) monojet and monophoton production plus missing energy at the Tevatron and the Large Hadron Collider (LHC). We combine the experimental data of relic density from WMAP7, spin-independent cross section from XENON100, spin-dependent cross section from XENON10, ZEPLIN-III, and SIMPLE, cosmic antiproton flux from PAMELA, cosmic gamma-ray flux from Fermi-LAT, and the monojet and monophoton data from the Tevatron and the LHC, to put the most comprehensive limits on each effective operator.

Interpretations of the ATLAS diboson anomaly

We present a global study of the simplest scalar phantom dark matter model. The best fit parameters of the model are determined by simultaneously imposing (i) relic density constraint from WMAP, (ii) 225 live days data from direct experiment XENON100, (iii) upper limit of gamma-ray flux from Fermi-LAT indirect detection based on dwarf spheroidal satellite galaxies, and (iv) the Higgs boson candidate with a mass about 125 GeV and its invisible branching ratio no larger than 40% if the decay of the Higgs boson into a pair of dark matter is kinematically allowed. The allowed parameter space is then used to predict annihilation cross sections for gamma-ray lines, event rates for three processes mono-b jet, single charged lepton and two charged leptons plus missing energies at the Large Hadron Collider, as well as to evaluate the muon anomalous magnetic dipole moment for the model.

Higgcision in the two-Higgs doublet models

We interpret the potential observation of the 750 GeV di-photon resonance at the LHC in models, in which an

An exploratory study of Higgs-boson pair production

SU(2)

The top window for dark matter

isospin-singlet scalar boson mixes with the Standard Model (SM) Higgs boson through an angle

Probing the Top-Yukawa Coupling in Associated Higgs production with a Single Top Quark

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