arXiv subjects
Publications and source records attributed to Kingman Cheung.
In this talk, I summarize a work done in collaboration with Otto Kong on the Zee neutrino mass model. We show that the MSSM with explicit R-parity violation actually contains the Zee model with the right-handed sleptons as the Zee singlet. We determine the conditions on the parameter space such that the neutrino mass matrix provides a viable texture that explains the atmospheric and solar data.
The success of the Randall-Sundrum scenario relies on stabilization of the modulus field or the radion, which is the scalar field about the background geometry. The stabilization mechanism proposed by Goldberger and Wise has the consequence that this radion is lighter than the graviton Kaluza-Klein states so that the first particle to be discovered is the radion. In this work, we study in details the decay, production, and detection of the radion at hadronic, $e^+ e^-$, and $γγ$ colliders.
In this talk, I briefly review collider signatures for two models of extra dimensions. The first one was proposed by Arkani-Hamed {\it et al.} that gravity is free to propagate in extra dimensions of very large size ($\alt 1$ mm). Collider signatures for this model can be divided into two types: (i) emission of real gravitons into extra dimensions, and (ii) exchanges of virtual gravitons. The second model was proposed by Pomarol {\it et al.} and Dienes {\it et al.} that the SM gauge bosons are allowed to propagate in extra dimensions. Collider signatures for the second model are due to the existence of the Kaluza-Klein (KK) states of $γ$, $W$, $Z$, and $g$ bosons.
We study the feasibility of incorporating the popular Zee model for neutrino mass in the framework of the supersymmetric standard model. While a singlet slepton has the right quantum number to play the role of the Zee charged scalar boson, the SUSY framework introduces extra contributions. We derive conditions for the Zee contributions to dominate, hence retaining the flavor of the Zee model.
The recent measurement of atomic parity violation in cesium atoms shows a $2.3σ$ deviation from the standard model prediction. We show that such an effect can be explained by four-fermion contact interactions with specific chiralities or by scalar leptoquarks which couple to the left-handed quarks. For a coupling of electromagnetic strength, the leptoquark mass is inferred to be 1.1 to 1.3 TeV. We also show that these solutions are consistent with all other low-energy and high-energy neutral-current data.
We study the Zee model of neutrino mass in the framework of R-parity violating supersymmetry. Within the matter contents of the minimal supersymmetric standard model, any one of the three right-handed sleptons could be a suitable candidate for the charged-singlet scalar of the Zee model, and one of the Higgs doublets provides the extra necessary vacuum expectation value. A combination of one bilinear and two trilinear R-parity-violating couplings then completes the model. In this framework, we also discuss other various contributions to neutrino masses and derive the conditions for the dominance of the contribution from the Zee model, and hence maintain the successfully Zee mass texture. However, this model within the minimal supersymmetric standard model is shown to be only marginally feasible. More general versions of supersymmetrization of the Zee model are also discussed. A particularly interesting example that has extra Higgs doublets while the slepton, especially the selectron, keeps the role of the Zee scalar is illustrated.
We discuss the physics potential of the $μp$ collider; especially, leptoquarks, leptogluons, R-parity violating squarks, contact interactions, and large extra dimensions. We calculate the sensitivity reach for these new physics at $μp$ colliders of various energies and luminosities.
CDF recently measured the quantity $\frac{σ(B_c^+)}{σ(B^+)} \frac{{\rm BR}(B_c^+ \to J/ψ\ell^+ ν)}{{\rm BR}(B^+ \to J/ψK^+)}$, {}from which we determine the ratio $\frac{σ(B_c^+)}{σ(\bar b)}$ to be $(2.08\err{1.06}{0.95})\times 10^{-3}$. In this note, we show that the ratio $\frac{σ(B_c^+)}{σ(\bar b)}$ obtained by dividing the $σ(B_c^+)$ by the leading order $σ(\bar b)$ is consistent with this derived CDF measurement. We calculate the cross section $σ(B_c^+)$ using the perturbative QCD fragmentation functions of Braaten, Cheung, and Yuan and the corresponding induced gluon fragmentation functions, with the charm-quark mass $m_c$ as a parameter. We also estimate the parameter $m_c$ from the CDF data and then predict the production rate at RunII.
In the model of Arkani-Hamed, Dimopoulos, and Dvali where gravity is allowed to propagate in the extra dimensions of very large size, virtual graviton exchange between the standard model particles can give rise to signatures that can be tested in collider experiments. We study these effects in dilepton and diphoton production at hadron colliders. Specifically, we examine the double differential cross-section in the invariant mass and scattering angle, which is found to be useful in separating the gravity effects from the standard model. In this work, sensitivity obtained using the double differential cross-section is higher than that in previous studies based on single differential distributions. Assuming no excess of events over the standard model predictions, we obtain the following 95% confidence level lower limits on the effective Planck scale: $0.9-1.5$ TeV in the Tevatron Run I, $1.3-2.5$ TeV in Run IIa, $1.7-3.5$ TeV in Run IIb, and $6.5-12.8$ TeV at the LHC. The range of numbers corresponds to the number of extra dimensions $n=7-2$.
Gravity can become strong at the TeV scale in the theory of extra dimensions. An effective Lagrangian can be used to describe the gravitational interactions below a cut-off scale. In this work, we study the associated production of the gravitons with a $Z$ boson or a photon at $e^+ e^-$ colliders of energies of LEPII to the Next Linear Colliders (NLC) ($\sqrt{s}=0.25-1.5$ TeV) and calculate the sensitivity to the new interactions. We also obtain the limit on the cut-off scale using the present data from LEPII.
We perform a global analysis of the lepton-quark neutral current data on the low scale gravity model, which arises from the extra dimensions. The global data include HERA neutral current deep-inelastic scattering, Drell-yan production at the Tevatron, and fermion pair production at LEPII. The Drell-yan production, due to the large invariant mass data, provides the strongest constraint. Combining all data, the effective Planck scale must be larger than about 1.12 TeV for $n=3$ and 0.94 TeV for $n=4$ at 95%CL.
Gravity can become strong at the TeV scale in the theory of extra dimensions. An effective Lagrangian can be used to describe the gravitational interactions below a cut-off scale. In this work, we study the diphoton production in $γγ$, $p\bar p$, and $e^+ e^-$ collisions in the model of low scale gravity. Since in the standard model photon-photon scattering only occurs via box diagrams, the cross section is highly suppressed. Thus, photon-photon scattering opens an interesting opportunity for studying the new gravity interaction, which allows tree-level photon couplings. In addition, we also examine the diphoton production at hadronic and $e^+ e^-$ colliders. We derive the limits on the cut-off scale from the available diphoton data and also estimate the sensitivity reach in Run II at the Tevaton and at the future linear $e^+ e^-$ colliders.
In a general two-Higgs-doublet model (2HDM), without the {\it ad hoc} discrete symmetries to prevent tree-level flavor-changing-neutral currents, an extra phase angle in the charged-Higgs-fermion coupling is allowed. We show that the charged-Higgs amplitude interferes destructively or constructively with the standard model amplitude depending crucially on this phase angle. The popular model I and II are special cases of our analysis. As a result of this phase angle the severe constraint on the charged-Higgs boson mass imposed by the inclusive rate of $b\to sγ$ from CLEO can be relaxed. We also examine the effects of this phase angle on the neutron electric dipole moment. Furthermore, we also discuss other constraints on the charged-Higgs-fermion couplings coming from measurements of $B^0-\bar{B^0}$ mixing, $ρ_0$, and $R_b$.
Measurements of neutral current processes off the $Z$-peak are sensitive probes of new interactions, which may be induced by the exchange of new particles such as leptoquarks or extra $Z$'s. This talk reviews the phenomenology of extra interactions in four-fermion processes and updates a global fit to contact terms in the neutral current sector.
We study, using a monte carlo approach, the rare decay $B\to X_s \ell^+ \ell^-$ including effects of the arbitrariness of the phase between the $ψ$ amplitudes and the perturbative amplitude, $b$-quark fermi motion inside the $B$ meson, and experimental smearing of lepton momenta. The fermi motion of $b$-quark inside the $B$ meson is modeled by the ACCMM model. We found that such effects reduce the sensitivities of the spectra of invariant mass and forward-backward asymmetry of the lepton pair to new physics; especially, in the neighborhood of the $ψ$ resonances. We also estimate the sensitivity range of Wilson coefficients with respect to the uncertainties.
In this talk, I summarize a global analysis on electron-quark contact interactions using the updated NC DIS data at HERA, Drell-yan production at the Tevatron, total hadronic cross sections at LEP, atomic parity violation measurement, low energy $e$-nucleon scattering data, and the $ν$-nucleon scattering data. The global data do not show any evidence for contact interactions. Thus, we obtain limits of 8--15 TeV on the compositeness scale, which are significantly better than those published by each individual experiment.
In the framework of gauge-mediated supersymmetry breaking models pair production of the lightest neutralinos, scalar leptons, or charginos at LEPII gives rise to interesting signals involving multilepton final states and missing energy. In the parameter space where the scalar tau, $\tildeτ_1$, is the next-to-lightest supersymmetric particle, we identify three interesting regions, which give rise to distinctly different final states: (i) 2 $τ$-leptons plus missing energy, (ii) 4 charged leptons plus missing energy where in some regions all four are $τ$-leptons, or (iii) six charged leptons, of which four are $τ$-leptons and the other two are electrons or muons, plus missing energy. We study in detail the size of these regions in the parameter space of gauge-mediated models and give cross section contours in these regions for various LEPII energies. We also discuss the possibility of chargino-pair production at LEPII.
The explanation of a 200 GeV R-parity violating squark to the HERA high-$Q^2$ anomaly would have an important impact on supersymmetry-breaking models. Here we show that a squark of mass around 200 GeV is disallowed in the minimal gauge-mediated SUSY-breaking models in the parameter space constrained by the radiative electroweak-symmetry breaking and the experimental lower limits on supersymmetric particles, even after including the large R-parity violating couplings. Supergravity motivated models can, on the other hand, give rise to these scalar quarks in a wide range of parameter space.