arXiv subjects

Kang Young Lee

Publications and source records attributed to Kang Young Lee.

At least 73 records · Page 4Linked to original sources

arXiv2002

Enhancement of epsilon'/epsilon in the SU(2)_L times SU(2)_R times U(1) model

We explore the possible enhancement of direct CP violating parameter epsilon'/epsilon in the general left-right model based on the SU(2)_L times SU(2)_R times U(1) gauge group. The mixing matrix of right-handed quarks, V_{CKM}^R is observable in the left-right model, and provides new source of CP violating phase. We calculate the parameter epsilon'/epsilon in the left-right model and show that the new phases from V_{CKM}^R can yield the sizable contribution to the direct CP violation enough to satisfy the recent measurements of Re(epsilon'/epsilon) from Fermilab KTeV and CERN NA48 experiments.

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arXiv2002

Probing anomalous right-handed top quark couplings in rare B decays

We explore the anomalous right-handed $\bar{t}sW$ and $\bar{t}bW$ couplings using $ B \to X_s γ$ and $B \to X_s l^+ l^-$ decays induced by the flavour-changing penguin diagrams. The anomalous $\bar{t}sW$ coupling can yield 10% enhancement of the $B \to X_s l^+ l^-$ decay rate under the constraint from the present $B \to X_s γ$ data, while it does not affect the forward-backward asymmetry of the charged lepton. The allowed region for anomalous $\bar{t}bW$ coupling by the $ B \to X_s γ$ constraint is two-fold, the small value region and the large value region. Though the effect of the small anomalous coupling on the $B \to X_s l^+ l^-$ branching ratio is very little, it can yield a substantial chanhge for the forward-backward asymmetry.

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arXiv2001

Probing large extra dimensions with spin configuration of top quark pair production at the JLC

We explore signatures of large extra dimensions with a polarized electron/positrn beam at the Joint Linear Collider (JLC). We point out that spin informations can be useful to study indirect signals for large extra dimensions due to spin-2 nature of Kaluza-Klein gravitons. The spin configurations of the top quark pair production at $e^+ e^-$ and $γγ$ collisions provide an unique testing ground to search for effects of the large extra dimensions. Especially we show the forward-backward asymmetry is a good probe at $e^+ e^- \to t \bar{t}$ process and we can define a new asymmetry observable effective for $γγ\to t \bar{t}$ process.

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arXiv2001

Probing the messenger of supersymmetry breaking by the muon anomalous magnetic moment

Motivated by the recently measured muon's anomalous magnetic moment $a_μ$, we examine the supersymmetry contribution to $a_μ$ in various mediation models of supersymmetry breaking which lead to predictive flavor conserving soft parameters at high energy scale. The studied models include dilaton/modulus-mediated models in heterotic string/$M$ theory, gauge-mediated model, no-scale or gaugino-mediated model, and also the minimal and deflected anomaly-mediated models. For each model, the range of $a^{SUSY}_μ$ allowed by other experimental constraints, e.g. b --> sγand the collider bounds on superparticle masses, is obtained together with the corresponding parameter region of the model. Gauge-mediated models with low messenger scale can give any $a^{SUSY}_μ$ within the $2σ$ bound. In many other models, b --> sγfavors $a^{SUSY}_μ$ smaller than either the $-1σ$ value ($26\times 10^{-10}$) or the central value ($42\times 10^{-10}$).

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arXiv2001

Implications of the muon anomalous magnetic moment and Higgs-mediated flavor changing neutral currents

In the light of the recent measurement of the muon anmalous magnetic moment $a_μ$ by the Muon $(g-2)$ Collaboration, we examine the contribution to $a_μ$ from the exchange of flavor changing scalars. Assuming that the heavier generations have larger flavor changing couplings, we obtain a bound on $μ- τ$ Yukawa coupling for a given scalar mass. Constraints on other flavor changing/conserving couplings are also obtained from the lepton flavor violating decays of muon and tau lepton, and bounds on the branching ratio of $τ\to 3 e$, $μ\to 3 e$ and $τ\to e μe$ processes are predicted.

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arXiv2001

Enhancement of the Higgs pair production at LHC; the MSSM and extra dimension effects

The neutral Higgs pair production at the LHC is studied in the MSSM, the large extra dimensional (ADD) model and the Randall-Sundrum (RS) model, where the total cross section can be significantly enhanced compared to that in the SM. The $p_{_T}$, invariant mass and rapidity distributions of each model have been shown to be distinctive: The ADD model raises the $p_T$ and invariant mass distributions at high scales of $p_T$ and invariant mass; in the RS model resonant peaks appear after the SM contribution dies away; the SM and the MSSM distributions drop rapidly at those high scales; in the ADD and the RS models the rapidity distributions congregate more around the center. It is concluded that various distributions of the Higgs pair production at the LHC with restrictive kinematic cuts would provide one of the most robust signals for the extra dimensional effects.

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arXiv2000

Probing Z' gauge boson with the spin configuration of top quark pair production at future $e^- e^+$ linear colliders

We explore the effects of extra neutral gauge boson involved in the supersymmetric E6 model on the spin configuration of the top quark pair produced at the polarized e- e+ collider. Generic mixing terms are considered including kinetic mixing terms as well as mass mixing. In the off-diagonal spin basis of the standard model, we show that the cross sections for the suppressed spin configurations can be enhanced with the effects of the Z' boson through the modification of the spin configuration of produced top quark pair enough to be measured in the Linear Colliders, which provides the way to observe the effects of Z' boson and discriminate the pattern of gauge group decomposition. It is pointed out that the kinetic mixing may dilute the effects of mass mixing terms, and we have to perform the combined analysis.

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arXiv1999

Spin configuration of top quark pair production with large extra dimensions at photon-photon colliders

Top quark pair production at photon-photon colliders is studied in low scale quantum gravity scenario. From the dependence of the cross sections on the spin configuration of the top quark and anti-quark, we introduce a new observable, top spin asymmetry. It is shown that there exists a special top spin basis where with the polarized parent electron beams the top spin asymmetry vanishes in the standard model but retains substantial values with the large extra dimension effects. We also present lower bounds of the quantum gravity scale $M_S$ from total cross sections with various combinations of the laser, electron beam, and top quark pair polarizations. The measurements of the top spin state $(t_\uparrow\bar{t}_\downarrow)$ with unpolarized initial beams are shown to be most effective, enhancing by about 5% the $M_S$ bounds with respect to totally unpolarized case.

hep-ph↗

arXiv1999

Polarization Effects on the $e+e- \to W^+W^-$ process with Large Extra Dimensions

We study large extra dimension effects on the polarizations of the $W$ pair and electron beam at the $e^+ e^-\to W^+ W^-$ process. It is shown that the measurements of the cross section for transversely polarized $W$ pair with the right-handed electron beam remarkably enhance the possibilities to see the low scale quantum gravity effects. Higher Linear Collider bounds on the string scale in this model can be obtained by using the left-handed electron beam.

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arXiv1999

Polarization effects on W boson pair productions with the extra neutral gauge boson at the e^+ e^- Linear Collider

We perform the comprehensive analysis of the polarization effects on the e^+e^- -> W^+W^- process in the presence of the extra neutral gauge boson at the LC energies. Consideration of the polarizations of the produced W bosons and the beam polarizations provides substantial enhancements of the sensitivity to the Z-Z' mixing angles in various models and the asymmetry variables also give the strict constraints on the mixing angles. We find that the χ-model and the left-right model get the strict constraint from σ_{LL}^{unpol} while the ψ-model and the η-model from the beam polarization asymmetry.

hep-ph↗

arXiv1999

Large Extra Dimension Effects on the Spin Configuration of the Top Quark Pair at e^+ e^- Colliders

Large extra dimension effects on the spin configuration of the top quark pair at the $e^+ e^-\to t\bar{t}$ process are studied. It is shown that the TeV scale quantum gravity effects cause significant deviations from the Standard Model predictions for the spin configuration in the off-diagonal basis: they lead to substantial cross sections of the like-spin states of the top quark pair, which vanish in the SM; they weaken the pure dominance of the processes, the Up-Down (Down-Up) spin states for the left-handed (right-handed) beam. In addition it is shown that the angular cut $-0.5<\cosθ<0$ is very effective to determine the sign of the quantum gravity corrections.

hep-ph↗

arXiv1999

Probing anomalous right--handed current in Z b bbar vertex

Motivated by $-2 σ$ deviation from the Standard Model prediction for the forward--backward asymmetry of $Z \to b \bar{b}$ decay in the LEP data, we explore the anomalous couplings of $Z b \bar{b}$ vertex through the electroweak precision test extended by including $A_{FB}^b$. We introduce a new variable $ε'_b$ to measure the anomalous right-handed coupling in $Z b \bar{b}$ vertex. Implications of our analysis on the nonuniversal contact interactions are studied and the left-right model is also considered as a possible origin of the anomalous right-handed couplings.

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arXiv1998

Complete analysis of photino-mediated lepton flavor violaitons in generalized supersymmetric models

We consider lepton flavor violations (LFV) mediated by photino as a result of the nondiagonal slepton mass matrices in general supersymmetric models. Using the experimental upper bounds on l \to l' + gamma and mu^- + Ti \to e^- + Ti as constraints on the flavor changing slepton mass insertions, we predict the possible ranges of the upper limits on the branching ratios of other LFV processes such as l \to 3l', tau \to l_{i\neq 3} + pi^0 (or eta, rho^0, phi), Z^0 \to l_i bar{l}_{j\neq i}, and muonium \to antimuonium conversion. Most of these decays are expected to occur with small branching ratios far below the current or future experimental search limits. We also derive constraints on the flavor conserving mass insertions from the anomalous magnetic moments of leptons.

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arXiv1998

Evolution equation for the heavy quark distribution function in the parton model approach

We explore the perturbative QCD corrections to the inclusive semileptonic decays of $B$ mesons. In inclusive $B$ decay processes the parton picture works well and the scaling feature manifests because the mass of $b$ quark is larger than the QCD scale. Due to this property, the decay rate may be expressed by a single structure function describing the light-cone distribution of $b$ quark apart from the kinematic factor. We derive a $q^2$ evolution equation for the distribution function, which violates the scaling property through the Altarelli-Parisi type approach. The evolution equation is numerically solved and its phenomenological implications are also discussed.

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arXiv1998

Bounds of the mass of Z' and the neutral mixing angles in general SU(2)_L x SU(2)_R x U(1) models

We consider phenomenological constraints on the mass $M_{Z^{\prime}}$ and the two mixing angles $θ_R$ and $ξ$ of the neutral sector in a very general class of $SU(2)_L \times SU(2)_R \times U(1)$ models using electroweak data. We do not make any specific assumptions such as left-right symmetry or the Higgs structure. The analysis of the neutral sector has the advantage that it has relatively fewer parameters compared to the charged sector since the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements in the right-handed sector do not enter into the analysis, hence the number of various possibilities from a big parameter space is reduced. We utilize theoretical considerations on the masses of the gauge particles and the mixing angles. We combine the precision electroweak data from LEP I and the low-energy neutral-current experimental data to constrain the parameters introduced in the model. It turns out that $M_{Z^{\prime}}> 400$ GeV, $-0.0028 <ξ<0.0065$ with little constraint on $θ_R$. In the left-right symmetric theory, $M_{Z^{\prime}}$ should be larger than 900 GeV. With these constraints, we compare the values for $σ(e^+ e^- \to μ^+ μ^-)$, $σ(e^+ e^- \to b\bar{b})$ and $A_{FB}^{\ell}$ at LEP II with experimental values.

hep-ph↗

arXiv1998

New Electroweak Tests for the Topflavour Model

We explore phenomenologies of the topflavour model for the LEP experiment at $m_{_Z}$ scale. Implications of the model on the $Z$ peak data are studied in terms of the precision variables $ε_i$'s.

hep-ph↗

arXiv1998

B-\bar{B} Mixings and Rare B Decays in the Topflavour Model

We explore the impact of topflavour model to $B-\bar{B}$ mixings and rare decays of $B$ mesons. By the flavour-changing neutral current interactions of this model, the $B-\bar{B}$ mixing amplitudes are substantially affected while it is hard to investigate the effects on rare decays. Violation of the unitarity of the CKM matrix is also discussed. We find that the bound on $|V_{td}|$ can be stronger in this model by combining the experimental bound of the $B-\bar{B}$ mixing and the bound from violated unitarity.

hep-ph↗

arXiv1998

Phenomenological Implications of the Topflavor Model

We explore phenomenologies of the topflavour model for the LEP experiment at $m_{_Z}$ scale and the atomic parity violation (APV) experiment in the $C_s$ atoms at low energies. Implications of the model on the $Z$ peak data are studied in terms of the precision variables $ε_i$'s. We find that the LEP data give more stringent constraints on the model parameters than the APV data.

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