arXiv subjects

Kingman Cheung

Publications and source records attributed to Kingman Cheung.

At least 181 records · Page 10Linked to original sources

arXiv2005

Hadronic production and decays of Charginos and Neutralinos in Split Supersymmetry

In the scenario recently proposed by Arkani-Hamed and Dimopoulos, the supersymmetric scalar particles are all very heavy, at least of the order of $10^9$ GeV but the gauginos, higgsino, and one of the CP-even neutral Higgs bosons remain light under a TeV. In addition to gluino production, the first SUSY signature would be pair production of neutralinos and/or charginos. Here we study, with explicit CP violation, the production of neutralinos and charginos at hadronic colliders as well as the possible decay modes. We notice that the branching ratio of the neutralino radiative decay can be sizable unlike the case with light sfermions. In particular, the decay of N3->N1+gamma has a branching ratio of the order O(1) percent. In colliders, it would give rise to signatures of an isolated single photon plus missing energy.

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arXiv2005

Constraints on String Resonance Amplitudes

We perform a global analysis of the tree-level open-string amplitudes in the limit $s << M_S^2$ . Based on the present data from the Tevatron, HERA, and LEP~2, we set a lower limit on the string scale $M_S >= 0.69 - 1.96$ TeV at 95 % confidence level for the Chan-Paton factors $|T|=0 - 4$. We also estimate the expected sensitivities at the LHC, which can be as high as 19 TeV for $|T|=4$.

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arXiv2005

Lepton Flavor Violation as a Probe of Quark-Lepton Unification

The recent measurements of the solar neutrino mixing angle theta_{sol} and the Cabibbo mixing angle theta_C reveal a surprising relation, theta_{sol}+theta_C ~ pi/4. Interpreting this empirical relation as a support of the quark-lepton unification, we find that the PMNS mixing matrix can be decomposed into a CKM-like matrix and maximal mixing matrices, which can give profound implications on the quark-lepton unification. We explore a possibility to probe the implication of quark-lepton unification by considering the relative sizes of branching ratios for the lepton flavor violating radiative decay processes, l_i-->l_j gamma, in the context of the supersymmetric standard model with heavy right-handed Majorana neutrinos.

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arXiv2005

Splitting the split supersymmetry

In split supersymmetry, the supersymmetric scalar particles are all very heavy, at least at the order of 10^9 GeV, but the gauginos, Higgsinos, and one of the neutral Higgs bosons remain below a TeV. Here we further split the split supersymmetry by taking the Higgsino mass parameter μto be very large. In this case, the μproblem is avoided and we keep the wino as a dark matter candidate. A crude gauge coupling unification is still preserved. Dark matter signals and collider phenomenology are discussed in this μ-split SUSY scenario. The most interesting dark matter signal is the annihilation into monochromatic photons. In colliders, chargino-pair and the associated chargino-neutralino production cross sections have a certain ratio due to gauge couplings, and the chargino has long decays.

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arXiv2004

Neutral Pion-like Resonances at Photon Colliders

Two photons can annihilate into a neutral pion-like resonance via the anomaly coupling, just like $π^0γγ$ in QCD. In some strongly interacting electroweak symmetry breaking models, e.g., technicolor type models, there often exist neutral pion-like resonances. TeV photon colliders have a strong capability to discover such particles, because the standard model background in photon scattering goes through box diagrams and is therefore highly suppressed. In this study, we perform a signal-background comparison. We show that $e^+ e^-$ linear colliders running in $γγ$ mode can discover such neutral-pion-like resonances with a decent sensitivity.

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arXiv2004

Collider Phenomenology for a few models of extra dimensions

In this talk, we summarize the collider phenomenology and recent experimental results for various models of extra dimensions, including the large extra dimensions (ADD model), warped extra dimensions (Randall-Sundrum model), TeV$^{-1}$-sized extra dimensions with gauge bosons in the bulk, universal extra dimensions, and an 5D SU(5) SUSY GUT model in AdS space.

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arXiv2004

Split Supersymmetry, stable gluino, and gluinonium

In the scenario recently proposed by Arkani and Dimopoulos, the supersymmetric scalar particles are all very heavy, at least of the order of $10^9$ GeV but the gauginos, higgsinos, and one of the neutral Higgs bosons remain under a TeV. The most distinct signature is the metastable gluino. However, the detection of metastable gluino depends crucially on the spectrum of hadrons that it fragments into. Instead, here we propose another unambiguous signature by forming the gluino-gluino bound state, gluinonium, which will then annihilate into $t\bar t$ and $b\bar b$ pairs. We study the sensitivity of such signatures at the LHC.

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arXiv2004

Light Strange-beauty Squarks

We summarize a study on the production, decay, and detection of the strange-beauty squark as light as 200 GeV at hadronic and $e^+ e^-$ colliders. It was motivated by nearly maximal mixing between strange and beauty squarks.

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arXiv2004

Some Physics Beyond the Standard Model at Gamma Gamma Colliders

In this talk, I describe a few interesting physics beyond the standard model that are quite unique for $γγ$ collisions, including large extra dimension model (ADD), warped extra dimension model (Randall-Sundrum) model, universal extra dimension model, as well as techni-pions of technicolor models.

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arXiv2004

Summary Report for the $e^- e^-$ session in LCWS 2004

In this talk, I summarize the activities in the $e^- e^-$ session. The consensus is that if the next generation $e^+ e^-$ linear collider wants to include an $e^- e^-$ option, the planning has to include it as early as possible. By doing so the extra cost would be only a small fraction of the total, and of course the physics potential would be very rewarding.

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arXiv2004

A note on Charmed and Bottomed Pentaquark Production by Fragmentation

H1 Collaboration recently observed the charmed pentaquark. In this short note, we point out that the dominant production mechanism for pentaquark consisting of a heavy quark is heavy quark fragmentation. We obtain a crude estimate on the fragmentation probability for charm quark into Theta_c^0, based on the known fragmentation probabilities of charm quark into mesons and baryons: f(c-bar --> Theta_c^0) =~ (2-7) x 10^{-3}. Similarly, we also obtain the fragmentation probability for bottom quark into Theta_b^+: f(b-bar --> Theta_b^+) =~ (5-20) x 10^{-3}. We also estimate the prospect of observing Theta_c^0 and Theta_b^+ at HERA, LEP, and Tevatron.

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arXiv2004

Pentaquark Theta+, constituent quark structures, and prediction of charmed Theta(c)^0 and bottomed Theta(b)^+

The newly observed $Θ^+$ resonance is believed to be a pentaquark with the constituent quarks $uudd\bar s$. There are a few options for the constituent quark structure. Some advocate diquark-diquark-antiquark $(ud)$-$(ud)$-$\bar s$ while others favor diquark-triquark $(ud)$-$(ud\bar s)$. We use the color-spin hyperfine interaction to examine the energy levels of these structures, and we find that the diquark-diquark-antiquark structure is slight favored. We proceed to write down the flavor triplet and antisextet of the charmed or bottomed exotic baryons with internal $qqqq\bar Q$ quarks. We also estimate the mass of $Θ_c^0$ and $Θ_b^+$.

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arXiv2004

Collider Phenomenology of Light Strange-beauty Squarks

Strong mixing between right-handed strange and beauty squarks is a possible solution to the CP violation discrepancy in $B\to ϕK_S$ decay as recently suggested by the Belle data. In this scenario, thanks to the strong mixing one of the strange-beauty squarks can be as light as 200 GeV, even though the generic supersymmetry scale is at TeV. In this work, we study the production of this light right-handed strange-beauty squark at hadronic colliders and discuss the detection in various decay scenarios. Detection prospect at the Tevatron Run II is good for the strange-beauty squark mass up to about 300 GeV.

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arXiv2004

Phenomenology of TeV Right-handed Neutrino and the Dark Matter Model

In a model of TeV right-handed (RH) neutrino by Krauss, Nasri, and Trodden, the sub-eV scale neutrino masses are generated via a 3-loop diagram with the vanishing see-saw mass forbidden by a discrete symmetry, and the TeV mass RH neutrino is simultaneously a novel candidate for the cold dark matter. However, we show that with a single RH neutrino it is not possible to generate two mass-square differences as required by the oscillation data. We extend the model by introducing one more TeV RH neutrino and show that it is possible to satisfy the oscillation pattern within the modified model. After studying in detail the constraints coming from the dark matter, lepton flavor violation and the muon anomalous magnetic moment, and the neutrinoless double beta decay, we explore the parameter space and derive predictions of the model. Finally, we study the production and decay signatures of the TeV RH neutrinos at TeV $e^+ e^-/μ^+ μ^-$ colliders.

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arXiv2003

Probing the Radion-Higgs mixing at hadronic colliders

In the Randall-Sundrum model, the radion-Higgs mixing is weakly suppressed by the effective electroweak scale. One of its novel features would be a sizable three-point vertex of KK graviton-Higgs-radion. We explored the potential of the Fermilab Tevatron and the CERN LHC in probing the radion-Higgs mixing via the associated production of the radion with the Higgs boson. The observation of the rare decay of the KK gravitons into a Higgs and a radion is then the direct and exclusive signal of the radion-Higgs mixing. We also studied all the partial decay widths of the KK gravitons in the presence of the radion-Higgs mixing, and found that if the mixing parameter is of order one, the decay rate into a radion and a Higgs boson becomes as large as that into a Higgs boson pair, with the branching ratio of order 0.001.

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arXiv2003

Belle J/psi+eta_c anomaly and a very light scalar boson

The large rate of the $J/ψ+η_c$ production observed by the Belle collaboration has posed a serious challenge to our understanding of the quarkonium. We examine a scenario that there exists a light scalar boson around 5 GeV, with an enhanced coupling solely to the charm quark. Such a scenario would explain the Belle anomaly. It also predicts a significant increase in $J/ψ$ plus open charm pair production. An immediate test for the scalar boson is to look for a peak around 5 GeV in the recoil mass spectrum of $J/ψ$, because the scalar boson can also be produced in association with the $J/ψ$. Finally, we also point out that the process $e^+ e^- \to H γ$ is sizable for observation.

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arXiv2003

TeV Colored Higgsinos in Alternative Grand Unified Theories

Recently, a type of GUT models with an extra dimension in AdS space can successfully solve the doublet-triplet problem, maintain proton stability, and allow the colored Higgs bosons and colored Higgsinos in the TeV mass region. We study the hadronic production and detection of these TeV colored Higgsinos and Higgs bosons. If the colored Higgsino is lighter than the colored Higgs boson, the colored Higgs boson will decay into a colored Higgsino and a gluino or a gravitino, and vice versa. The signatures would be stable massive charged particles with jets or missing energies.

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arXiv2003

Can the Two-Higgs-Doublet Model Survive the Constraint from the Muon Anomalous Magnetic Moment as Suggested?

Requiring the two-Higgs-doublet model II to accommodate the 3$σ$ deviation in the muon anomalous magnetic moment imposes specific constraints on the Higgs spectrum. We analyze the combination of all the relevant, available, constraints on the model parameter space. The use of constraints from $b\to s γ$, the precision electroweak measurements of $R_b$, and the $ρ$ parameter, together with exclusions from direct searches at LEP, give extremely severe restrictions on the model parameters. That is "almost enough" to kill the model altogether. The exclusion would be even stronger if the direct searches can be optimized to complement the other constraints, as will be discussed in details in this work.

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