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Han Liang

Publications and source records attributed to Han Liang.

At least 73 records · Page 4Linked to original sources

Probing Lepton Flavor Violation Signal Induced by R-violating Minimal Supersymmetric Standard Model at a Linear Collider

The lepton-flavor violation (LFV) effect at an $e^+e^-$ linear collider (LC), in the frame of R-parity violating minimal supersymmetric standard model is studied. We take the R-parity violating processes $e^+e^-\to e^{\mp}μ^{\pm}$ as signal, and define the summation of the two processes as ``experiment'' observable. We find that the cross-section summation can reach $\cal{O}$$(10^1)fb$ in the parameter space without sneutrino resonance effect($\sqrt{s} \sim m_{\tildeν}$). The summation treatment manifests uniform differential distribution on $\cosθ$, where $θ$ denotes the polar angles of both outgoing $e^+/e^-$ respectively to incoming electron beam in two signal processes. The uniform feature together with $eμ$ collinearity would help to reduce the SM background dramatically. Consequently we conclude that at a $500 GeV$ LC with $480 fb^{-1}$ annual luminosity, it's either possible to detect the distinctive R-violating LFV $eμ$ signal, or exclude sneutrino to $m_{\tildeν}>1.1 TeV$ at 95% CL in the machine's biennial runtime interval.

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Single chargino production with R-parity lepton number violation in photon-photon collisions

We examine the process $γγ\to \tildeχ^{+} τ^{-}$ at photon-photon collider in the minimal supersymmetric standard model(MSSM) with R-parity violation, where all the one-loop diagrams are considered. We mainly discuss the effects of bilinear breaking terms, and conclude that their contributions may be important compared with trilinear terms. Our results show that the events of this process could be detectable at photon-photon colliders, if the values of the parameters are favorable.

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Single chargino production via gluon-gluon fusion in a supersymmetric theory with an explicit R-parity violation

We studied the production of single chargino$\tildeχ_1^{\pm}$ accompanied by $μ^{\mp}$ lepton via gluon-gluon fusion at the LHC. The numerical analysis of their production rates is carried out in the mSUGRA scenario with some typical parameter sets. The results show that the cross sections of the $\tildeχ_1^{\pm}μ^{\mp}$ productions via gluon-gluon collision are in the order of $1 \sim 10^{2}$ femto barn quantitatively at the CERN LHC, and can be competitive with production mechanism via quark-antiquark annihilation process.

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Pair production of neutralinos via photon-photon collisions

We investigated the production of neutralino pairs via photon-photon collisions in the minimal supersymmetric model(MSSM) at future linear colliders. The numerical analysis of their production rates is carried out in the mSUGRA scenario. The results show that this cross section can reach about 18 femto barn for $\tildeχ^{0}_{1} \tildeχ^{0}_{2}$ pair production and 9 femto barn for $\tildeχ^{0}_{2}\tildeχ^{0}_{2}$ pair production with our chosen input parameters.

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$γγ\to t\bar{c}+c\bar{t}$ in a supersymmetric theory with an explicit R-parity violation

We studied the process $γγ\to t\bar{c}+c\bar{t}$ in a $R_{p}$ violating supersymmetric Model with the effects from both B- and L-violating interactions. The calculation shows that it is possible to detect a $R_{p}$ violating signal at the Next Linear Collider. Information about the B-violating interaction in this model could be obtained under very clean background, if we take the present upper bounds for the parameters in the supersymmetric $\rlap/ R_{p}$ interactions. Even if we can not detect a signal of $\rlap/R_{p}$ in the experiment, we may get more stringent constraints on the heavy-flavor $\rlap/R_{p}$ couplings.

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Neutralino pair production at proton-proton collider

In this paper we investigated the Drell-Yan process of the light neutralino pair $\tildeχ^0_{i}\tildeχ^0_{j}~(i,j=1,2)$ productions at hadron colliders. We studied the dependence of the coupling properties of two light neutralino $\tildeχ^0_{1,2}$ on the three SUSY Lagrangian parameters $M_1$, $M_2$ and $μ$, and find that the production rate of $\tildeχ^0_1 \tildeχ^0_2$ pair will be dominated by the Higgsino-like couplings under the condition $μ\ll M_2$ and $μ\sim M_1$, while the productions of $\tildeχ^0_1\tildeχ^0_1$ and $\tildeχ^0_2\tildeχ^0_2$ pairs will be enhanced by the gaugino-like couplings under $M_i \ll μ$. For the Higgsino-like $\tildeχ^0_{1,2}$ neutralinos, the cross section of $\tildeχ^0_1\tildeχ^0_2$ production at the LHC can reach $100~fb$.

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Probing R-parity violation in the production of $t \bar{c}(c \bar{t})$ on the lepton colliders

We studied the process $e^{+}e^{-} \to t\bar{c}+c\bar{t}$ in a R_{p} violating supersymmetric model with effects from both B- and L-violating interactions. The calculation shows that it is possible to either detect the R_{p} violating signal at the Next Linear Collider or get more stringent constraints on the heavy-flavor $\rlap/R_{p}$ couplings. A comparision with results from $γγ\to t\bar{c}+ c\bar{t}$ may allow to distinguish between B- and L-violating interactions. For very clean background conditions and R_{p} violation parameters close to present limits, a future detection of B-violating interactions should be possible. The process of $μ^{+} μ^{-} \to t \bar{c}+c\bar{t}$ is also considered.

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The SUSY EW-like corrections to top pair production in photon-photon collisions

We studied the one-loop contributions of the gaugino-Higgsino-sector to the process of top-pair production via $γγ$ fusion at NLC in frame of the Minimal Supersymmetric Model(MSSM). We find that the corrections to $γγ\to t\bar{t}$ and $e^+ e^- \to γγ\to t\bar{t}$ are found to be significant and can approach to a few percent and one percent, respectively. Furthermore, the dependences of the corrections on the supersymmetric parameters are also investigated. The corrections are not sensitive to $M_{SU(2)}$ (or $|μ|$) when $M_{SU(2)}~>>~|μ|$ (or $|μ|~>>~M_{SU(2)}$) and are weakly dependent on the $\tanβ$ with $M_Q$ (or $|μ|$) being large enough. But they are sensitive to the c.m.s. energy of the incoming photons.

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Pair Production of the Lightest Chargino via Gluon-Gluon Collisions

The production of the lightest chargino pair from gluon-gluon fusion is studied in the minimal supersymmetric model(MSSM) at proton-proton colliders. We find that with the chosen parameters, the production rate of the subprocess can be over 2.7 femto barn when the chargino is higgsino-like, and the corresponding total cross section in proton-proton collider can reach 56 femto barn at the LHC in the CP-conserving MSSM. It shows that this loop mediated subprocess can be competitive with the standard Drell-Yan subprocess in proton-proton colliders, especially at the LHC. Furthermore, our calculation shows it would be possible to extract information about some CP-violating phase parameters, if we collected enough chargino pair events.

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One-loop quark and squark corrections to the lightest chargino pair production in photon-photon collisions

We present the detailed analytical and numerical investigations of the one-loop radiative corrections of all quarks and squarks in the MSSM to the lightest chargino pair production via $γγ$ fusion at the future NLC. The numerical corrections show that the cross sections of the subprocess and the parent process are typically enhanced by several percent. We studied also the effects induced by the CP violating complex phases stemming from squark and chargino mass matrices in the MSSM at one-loop level.

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Top-quark pair production via polarized and unpolarized protons in the supersymmetric QCD

The QCD corrections to the top-quark pair production via both polarized and unpolarized gluon fusion in $pp$ collisions are calculated in the Minimal Supersymmetric Model(MSSM). We find the MSSM QCD corrections can reach 4% and may be observable in future precise experiments. Furthermore, we studied the CP violation in the MSSM, our results show that the CP violating parameter is sensitive to the masses of SUSY particles (It becomes zero, when the c.m. energy is less than twice the masses of both gluino and stop quarks.) and may reach $10^{-3}$.

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CP Violation in $γγ\to t~\bar{t}$ within the Minimal Supersymmetric Standard Model

The complete analysis of the CP violation in the process $γγ\to t \bar{t}$ in frame of the Minimal Supersymmetric Model(MSSM) is presented. The CP-odd observables for describing the CP violating effects in polarized and unpolarized photon collisions, are calculated. We investigate the possible CP violation sources induced by the complex soft breaking parameters and study the CP violating effects contributed by gluino, neutralino and chargino sectors appearing in the loop diagrams. We find that it is possible to observe the CP violation effects in top quark pair production via polarized and unpolarized photon fusions by using optimal observables and favorable parameters.

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Bounds on Schrödinger Energies

Elementary introduction to the application of Mathematica 3.0 to the solution of bound-state problems in quantum theory by standard variational procedures, with particular emphasis on the computation of precise upper bounds on energy levels of the system under consideration.

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CP violation in the annihilation $e^{+}~e^{-} \to t~\bar{t}$ within the Model-III of the two-Higgs-doublet extension

The CP-violating effects are studied in the electron-positron annihilation to produce $t\bar{t}$ pair within the Model-III of the two-Higgs-doublet extensions, which allows flavor changing neutral currents via Higgs exchanges. Complete analytical expressions for the form factors of the top quark electric and weak dipole moment induced in the framework of the model are presented. Several observables sensitive to the CP violation are calculated. The dependences of the CP-violating effects on Higgs boson masses and the possible phase angles are discussed. We find that the CP-violating observables can be of the order of $10^{-4}$ in general but may reach to $10^{-3}$ for the most favorable parameters in the model.

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Probing flavor changing interactions in photon-photon collisions

We examine the subprocess $γγ\to t\bar{c}+\bar{t}c$ at electron-positron colliders in the two-Higgs-doublet model with flavor-changing scalar couplings, where all the one-loop contribuions are considered, and the results are applicable to the whole mass range of the weakly coupled Higgs bosons. Because of the heavy top quark mass, this process is important in probing the flavor-changing top-charm-scalar vertex and could be detectable at the Next Linear Collider, if the values of the parameters are favorable. The results show that this process is more promising than the direct $e^{+} e^{-}$ process for discovering flavor changing scalar interactions.

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SUSY charged Higgs boson pair production via gluon-gluon collisions

The production of charged Higgs boson pairs from gluon-gluon fusion is studied in the minimal supersymmetric model(MSSM) at proton-proton colliders. We find that the contribution of the scalar quark loops to the subprocess production rate is substantial and consequently the production rate in proton-proton colliders is enhanced in the MSSM if there exist scalar quarks with favorable masses. The results show that this cross section may reach a few femptobarn in the future LHC collider with plausible values of the parameters.

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SUSY QCD corrections to W $γ$ production in polarized hadronic collisions

We present the calculation of the supersymmetric QCD correction to $W γ$ production process in polarized proton-antiproton collisions at the TeV energy region. We find that the correction can reach 1.2% at parton level with favorable mass values of squarks and gluino, which is comparable with the virtual correction part of the conventional QCD. The production rates for different polarized $p \bar{p}$ collisions are also compared.

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Pair production of charged Higgs bosons in gluon-gluon collisions

We studied the pair production rate of charged Higgs bosons via gluon-gluon collisions in the general two-Higgs-doublet model. The analysis of its production are made with possible parameter values of Higgs sectors in this model. We find that the production cross sections may be 4 to 41 fermi-bar in the future LHC pp collider with these parameters. The calculation also shows that this pair production process is not sensitive to the neutral Higgs masses, therefore its measurment could not give more imformations about the neutral Higgs bosons.

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