arXiv subjects

Kingman Cheung

Publications and source records attributed to Kingman Cheung.

At least 145 records · Page 8Linked to original sources

arXiv2009

Right-Handed Sneutrino Curvaton and non-Gaussianity

In this paper, we explore the parameter space for a Right-Handed (RH) sneutrino curvaton that can generate large non-Gaussianity without assuming any particular inflation sector. The mass of the RH sneutrino is suggested from a discussion on the initial condition of the curvaton field. It is shown that a small Yukawa coupling is generally required for a successful RH sneutrino curvaton. However, the Yukawa coupling can be larger if we consider the braneworld scenario. Some general discussion about the spectral index in curvaton scenario is also provided.

hep-ph↗

arXiv2009

Top Quark Forward-Backward Asymmetry

The recent forward-backward asymmetry recorded by the CDF Collaboration for the top and anti-top quark pair production indicates more than $2σ$ 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 erstwhile in the literature that can produce such effects are also discussed.

hep-ph↗

arXiv2009

Higgs boson enhancement effects on squark-pair production at the LHC

We study the Higgs boson effects on third-generation squark-pair production in proton-proton collision at the CERN Large Hadron Collider (LHC), including $\Stop \Stop^*$, $\Stop\Sbot^*$, and $\Sbot \Sbot^*$. We found that substantial enhancement can be obtained through s-channel exchanges of Higgs bosons at large $\tanβ$, at which the enhancement mainly comes from $b\bar b$, $b\bar c$, and $c\bar b$ initial states. We compute the complete set of electroweak (EW) contributions to all production channels. This completes previous computations in the literature. We found that the EW contributions can be significant and can reach up to 25% in more general scenarios and at the resonance of the heavy Higgs boson. The size of Higgs enhancement is comparable or even higher than the PDF uncertainties and so must be included in any reliable analysis. A full analytical computation of all the EW contributions is presented.

hep-ph↗

arXiv2009

Electric and anomalous magnetic dipole moments of the muon in the MSSM

We study the electric dipole moment (EDM) and the anomalous magnetic dipole moment (MDM) of the muon in the CP-violating Minimal Supersymmetric extension of the Standard Model (MSSM). We take into account the contributions from the chargino- and neutralino-mediated one-loop graphs and the dominant two-loop Higgs-mediated Barr-Zee diagrams. We improve earlier calculations by incorporating CP-violating Higgs-boson mixing effects and the resummed threshold corrections to the Yukawa couplings of the charged leptons as well as that of the bottom quark. The analytic correlation between the muon EDM and MDM is explicitly presented at one- and two-loop levels and, through several numerical examples, we illustrate its dependence on the source of the dominant contributions. We have implemented the analytic expressions for the muon EDM and MDM in an updated version of the public code CPsuperH2.0.

hep-ph↗

arXiv2009

Supernatural A-term Inflation

Following \cite{Lin:2009yt}, we explore the parameter space of the case when the supersymmetry (SUSY) breaking scale is lower, for example, in gauge mediated SUSY breaking model. During inflation, the form of the potential is $V_0$ plus MSSM (MSSM stands for Minimal Supersymmetric Standard Model) (or A term (It is called A-term inflation when the inflaton field is any direction (gauge or singlet) that generates an A-term.)) inflation. We show that the model works for a wide range of the potential $V_0$ with the soft SUSY breaking mass $m\sim O(1)$ TeV. The implication to MSSM (or A-term) inflation is that the flat directions which is lifted by the non-renormalizable terms described by the superpotential $W=λ_p ϕ^{p-1}/M^{p-3}_P$ with $p=4$ and $p=5$ are also suitable to be an inflaton field for $λ_p=O(1)$ provided there is an additional false vacuum term $V_0$ with appropriate magnitude. The flat directions corresponds to $p=6$ also works for $0 \lae V_0/M_P^4 \lae 10^{-40}$.

hep-ph↗

arXiv2009

Impact on the Light Higgsino-LSP Scenario from Physics beyond the Minimal Supersymmetric Standard Model

The modest addition of the dimension-5 term lambda(H_u.H_d)^2/M to the superpotential of the minimal supersymmetric standard model (MSSM) originated from physics beyond the MSSM (BMSSM) has a significant impact on the scenario of the Higgsino-dominated neutralino state being the lightest supersymmetric particle (LSP). It increases the mass difference between the LSP and the lighter chargino as well as that between the LSP and the second-lightest neutralino. This enhances the LHC discovery potential of the chargino and neutralino decays, producing more energetic charged leptons or pions than the decays without the BMSSM corrections. Furthermore, the coannihilation between the lighter chargino or second-lightest neutralino and the LSP is reduced substantially such that the LSP mass does not have to be very heavy. Consequently, an almost pure Higgsino LSP with its mass ~100 GeV in the BMSSM can account for all the relic density of cold dark matter in the Universe unless tan(beta) is too large.

hep-ph↗

arXiv2009

Double-action dark matter, PAMELA and ATIC

Motivated by a two-bump (or 1-peak plus 1-hump) structure in the ATIC data, we perform a statistical analysis fitting the PAMELA and ATIC data to a dark matter model, in which the dark matter particle can undergo both annihilation and decay. Using a chi-square analysis we show that both data can be simultaneously fitted better with such a double-action dark matter particle. We use an existing neutrino mass model in literature to illustrate the idea.

hep-ph↗

arXiv2009

Reducing the Spectral Index in Supernatural Inflation

Supernatural inflation is an attractive model based just on a flat direction with soft SUSY breaking mass terms in the framework of supersymmetry. The beauty of the model is inferred from its name that the model needs no fine-tuning. However, the prediction of the spectral index is $n_s \gae 1$, in contrast to experimental data. In this paper, we show that the beauty of supernatural inflation with the spectral index reduced to $n_s=0.96$ without any fine-tuning, by considering the general feature that a flat direction is lifted by a non-renormalizable term with an A-term.

hep-ph↗

arXiv2009

Super Hilltop Inflation

In this paper, we consider logarithmic radiative corrections and higher order terms to the supersymmetric hilltop F- and D-term hybrid inflation models. Conventional F- and D-term hybrid inflation only predicts $n_s \gae 0.98$. We show that via a positive quadratic and a negative quartic correction the spectral index can be reduced to $n_s=0.96$ suggested from latest WMAP result and also cosmic string problem appeared in SUSY hybrid inflation can be solved with mild tuning of the parameters if $κ\lae 0.01$ for F-term inflation and $g \lae 0.05$ for D-term inflation.

hep-ph↗

arXiv2008

Phenomenology of iQuarkonium

Phenomenology of uncolored iquarks - hypothetical fermions charged under a new confining unbroken non-abelian gauge group as well as the standard electroweak gauge group - is investigated for the iquark mass in the range near and above 100 GeV. If the new confining scale turns out to be higher than MeV but much less than the iquark mass, the iquark-antiiquark pair produced in the collider will promptly relaxed into the ground state of the iquarkonium. Subsequent pair annihilation into standard model particles gives useful information of the iquark dynamics. We formulate in details production and decays of the iquark-antiiquark bound states. Decay patterns of the iquarkonium can be distinguished from the superheavy quarkonium of a sequential fourth generation of quarks with degenerate mass.

hep-ph↗

arXiv2008

Unparticle Phenomenology -- A Mini Review

We review some collider phenomenology of unparticle physics, including real emissions and virtual exchanges of unparticle. Existing experimental constraints from collider physics as well as astrophysics are briefly discussed.

hep-ph↗

arXiv2008

Light Pseudoscalar Higgs boson in Neutralino Decays in the Next-to-Minimal Supersymmetric Standard Model

We point out another important production channel of a light pseudoscalar Higgs boson $a_1$ via the decays of neutralinos, including $\widetildeχ_{2,3}^0 \to \widetildeχ_{1}^0 a_1$, in the framework of the NMSSM. We scan the whole parameter space using the most up-to-date version of NMHDECAY and search for regions where $B(\widetildeχ_{2,3}^0 \to \widetildeχ_{1}^0 a_1) > 0.5$. If the gluino and squarks are light enough for copious production of SUSY events at the LHC, there would be numerous number of $\widetildeχ_{2,3}^0$ in subsequent decays of gluinos and squarks. Therefore, the production rates of $a_1$ via neutralino decays would be more important than $h \to a_1 a_1$ and others. Potentially, the final state is filled with many $τ$ leptons, which can be reconstructed at the mass of $a_1$. This is a clean, observable, and distinguishable signature for NMSSM.

hep-ph↗

arXiv2008

Production and decays of the light pseudoscalar boson $η$ at the LHC in the simplest little Higgs model

In many extensions of the standard model, the Higgs sector often contains an additional pseudoscalar boson. A good example is the SU(3) simplest little Higgs model, which accommodates a light pseudoscalar boson $η$ with quite different characteristics from those in other multi-Higgs-doublet models. We study various phenomenological signatures of the $η$ at the LHC. In particular, we calculate in details both production and decays in the Drell-Yan type channel $q \bar{q} \to Z/Z' \to h η$, and in the associated production with a $t\bar t$ pair, $gg (q\bar q) \to t \bar t η$. We emphasize the $τ^+ τ^-$ decay mode of the $η$ boson when its mass is below the $b\bar b$ threshold. We show that $t\bar t η$ production is in fact large enough to give a sizable number of events while suppressing the backgrounds. We also comment on the direct gluon fusion process and the indirect decay from the heavy $T$ quark ($T \to t η$)

hep-ph↗

arXiv2008

Partially Strong WW Scattering

What if only a light Higgs boson is discovered at the CERN LHC? Conventional wisdom tells us that the scattering of longitudinal weak gauge bosons would not grow strong at high energies. We show that this is not always true. In some composite models, two-Higgs-doublet models, or even supersymmetric models, the presence of a light Higgs boson does not guarantee the complete unitarization of the $WW$ scattering. After the partial unitarization by the light Higgs boson, the $WW$ scattering becomes strongly interacting until it hits one or more heavier Higgs bosons or other strong dynamics. We analyze how the LHC experiments can reveal this interesting possibility of partially strong $WW$ scattering.

hep-ph↗

arXiv2008

Unparticle effects in photon-photon scattering

Elastic photon-photon scattering can only occur via loop diagrams in the standard model and is naturally suppressed. Unparticle can induce tree-level photon-photon scattering through the operator F_{μν} F^{μν} O_\U for spin-0 unparticle or F_{μα} F^α_ν O^{μν}_\U for spin-2 unparticle. Due to the peculiar CP-conserving phase \exp(-i d_\U π) associated with the s-channel unparticle propagator, its interference effects with the t- and u-channels on the total cross section and the angular distribution are found to be some significance. In addition, we show that the cross sections via unparticle exchange can be substantially larger than the standard model contribution.

hep-ph↗

arXiv2008

Decay of Z Boson into Photon and Unparticle

We study the decay of the standard model Z boson into unparticle plus a single photon through a one-loop process. As in the anomaly type decay, only the axial-vector part of the Z coupling matching with the vector unparticle and/or the vector part of the Z coupling matching with the axial-vector unparticle can give a nonzero contribution to the decay. We show that the photon spectrum terminates at the end point in accord with Yang's theorem. Existing data on single photon production at LEP I is used to constrain the unparticle sector.

hep-ph↗

arXiv2007

Higgs Boson Decays into Single Photon plus Unparticle

The decay of the standard model Higgs boson into a single photon and a vector unparticle through a one-loop process is studied. For an intermediate mass Higgs boson, this single photon plus unparticle mode can have a branching ratio comparable with the two-photon discovery mode. The emitted photon has a continuous energy spectrum encoding the nature of the recoil unparticle. It can be measured in precision studies of the Higgs boson after its discovery.

hep-ph↗

arXiv2007

Hidden Fermion in Stueckelberg Z' Models as Milli-charged Dark Matter

The hidden Stueckelberg Z' model is augmented by a pair of Dirac fermions. If the Z' has a coupling strength comparable to weak scale coupling, one can show that this hidden fermion-antifermion pair could be a milli-charged dark matter candidate with a viable relic density. Monochromatic photon flux coming from the Galactic center due to pair annihilation of these milli-charged particles is calculated and is shown to be within reach of the next generation gamma-ray experiments. Characteristic collider signature of this theoretical endeavor is that the Stueckelberg Z' boson has a large invisible width decaying into the hidden fermion-antifermion pair if kinematically allowed. Singly production of this Z' boson at the LHC and ILC are studied.

hep-ph↗