arXiv subjects

Kang Young Lee

Publications and source records attributed to Kang Young Lee.

83 records · Page 5Linked to original sources

arXiv1997

Implications of the recent CERN LEP data on nonuniversal interactions with the precision electroweak tests

We explore the nonuniversal interaction effects in terms of the precision variables epsilons with the recent LEP data reported by the Electroweak Working Group. The epsilon variables with the nonuniversal interactions are calculated and constrained by the experimental ellipses in the $ε_1$--$ε_b$, $ε_2$--$ε_b$, and $ε_3$--$ε_b$ planes. We find that the new data enables us to make a stringent test on the correction to $Z \to b \bar{b}$ vertex. The $ε_b$ variable is sensitive to the $Z b \bar b$ couplings and thus plays a major role to give constraints on the nonuniversal interaction effects. Upon imposing the new data on $ε_b$, we have the allowed range of the model parameter $κ_L = 0.0063 \pm 0.0030$ at 1-$σ$ level with $m_t = 175$ GeV. Along with the minimal contact term, we predict the new physics scale $Λ\sim$ 1.6 TeV. By combining the experimental results from all planes we obtain the allowed range of $κ_L$ : $0.003 < κ_L < 0.010$ at 95 % C.L..

hep-ph↗

arXiv1997

New Precision Electroweak Tests in Supergravity Models

We update the analysis of the precision electroweak tests in terms of 4 epsilon parameters, $ε_{1,2,3,b}$, to obtain more accurate experimental values of them by taking into account the new LEP data released at the 28th ICHEP (1996, Poland). We also compute $ε_1$ and $ε_b$ in the context of the no-scale $SU(5)\times U(1)$ supergravity model to obtain the updated constraints by imposing the correlated constraints in terms of the experimental ellipses in the $ε_1-ε_b$ plane and also by imposing the new bound on the lightest chargino mass, $m_{χ^\pm_1}\gtrsim 79$ $ GeV$. Upon imposing these new experimental results, we find that the situations in the no-scale model are much more favorable than those in the standard model, and if $m_t\gtrsim 170$ $ GeV$, then the allowed regions at the 95% C.~L. in the no-scale model are $\tanβ\gtrsim 4$ and $m_{χ^\pm_1}\lesssim 120 (82)$ $ GeV$ for $μ>0 (μ<0)$, which are in fact much more stringent than in our previous analysis. Therefore, assuming that $m_t\gtrsim 170$ $ GeV$, if the lightest chargino mass bound were to be pushed up only by a few GeV, the sign on the Higgs mixing term $μ$ in the no-scale model could well be determined from the $ε_1-ε_b$ constraint to be positive at the 95% C.~L. At any rate, better accuracy in the measured $m_t$ from the Tevatron in the near future combined with the LEP data is most likely to provide a decisive test of the no-scale $SU(5)\times U(1)$ supergravity model.

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arXiv1996

Form Factors for Exclusive Semileptonic $B$--Decays

We investigate the form factors for exclusive semileptonic decays of $B$-meson to $D,~D^*$, based on the parton picture and helped by the results of the HQET. We obtain the numerical results for the slope of the Isgur-Wise function, which is consistent with the experimental results, and we extracte the dependences of hadronic form factors on $q^2$ by varying input heavy quark fragmentation function without the nearest pole dominance ansätze.

hep-ph↗

arXiv1996

The Parton Model Approach to Inclusive B meson Decays

We test the parton model approach to inclusive $B \ra γX_s$ and $B \ra e \barν X_u$ processes by calculating a few moments of the distribution function. The $1/m_Q$ expansion of $b$-quark distribution function is discussed. We show that Peterson's fragmentation function is useful as the distribution function of $b$-quark but requires some improvements. By extension of Peterson's arguments, we obtain the refined form for the distribution function and with the refined function, we obtain the consistent results with the HQET.

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arXiv1996

$a_1 (1260)$ contribution to photon and dilepton productions from hot hadronic matter : Revisited

We consider the $a_{1} (1260)$ contribution to photon and dilepton productions from hot hadronic matter. The effective lagrangian with $π, ρ$ and $a_{1}$ discussed by Ko and Rudaz is employed, which successfully reproduces the $Γ(a_{1} \rightarrow πγ) = 670$ keV. Our results for the photon production rate are comparable to those obtained by Xiong {\it et al.}, while the dilepton production rates come out smaller than those obtained by Gale {\it et al.} by an order of magnitude.

hep-ph↗

arXiv1995

$α_s(M_Z^2)$ and $R_b$ discrepancy with nonuniversal interactions

We implement global fits to LEP data with the \non interactions. Consistent $R_b$ with experimental value and consistent $\as(M_Z^2)$ with that from low energy experiments are obtained. We also find that the $\xx$ is better than the Standard Model. And we argue that other kinds of new physics are needed to explain the difference between the values of $\as(M_Z^2)$ from low energy experiments and from the 3-jet ratio.

hep-ph↗

arXiv1995

Approximate Flavour Symmetries and See-Saw Mechanism

We study the approximate flavour symmetries imposed on the lepton sector assuming see-saw mechanism as the neutrino mass structure. We apply the symmetry to various neutrino phenomenologies and obtain constraints on neutrino masses and mixings.

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arXiv1995

Form Factors for Exclusive Semileptonic $B$--Decays

We developed the new parton model approach for exclusive semileptonic decays of $B$-meson to $D,~D^*$ by extending the inclusive parton model, and by combining with the results of the HQET, motivated by Drell-Yan process. Without the nearest pole dominance ansätze, we {\bf derived} the dependences of hadronic form factors on $q^2$. We also calculated numerically the slope of the Isgur-Wise function, which is consistent with the experimental results.

hep-ph↗

arXiv1995

$K_{L e5}$ decay as a background in search for $K_{L} \to π^{0} μ^{\pm} e^{\mp}$

We consider a process $K_{L e5} ( K_{L} \rightarrow π^{0} π^{0} π^{\pm} e^{\mp} ν)$ as a standard model background to the experiment $K_{L} \rightarrow π^{0} μ^{\pm} e^{\mp}$, which seeks for possible violation of lepton family number. Using the lowest order chiral lagrangian, we find that the branching ratio for $K_{L} \rightarrow π^{0} π^{0} π^{\pm} e^{\mp} ν$ to be $6.2 \times 10^{-12}$. A similar decay $K_{L} \rightarrow π^{\mp} π^{\mp} π^{\pm} e^{\pm} ν$ has a branching ratio, $1.7 \times 10^{-11}$.

hep-ph↗

arXiv1995

$B \rightarrow τνX$ decays in a two Higgs doublet model

We calculate the decay rate for inclusive $B \rightarrow τνX$ decays in a two Higgs doublet model using heavy quark expansion and operator product expansion. Combined with the recent measurement of Br($B \ra τνX$), we find a limit $\tan β< 0.58 m_H/\mbox{GeV}$ at 90\%\ C.L..

hep-ph↗

arXiv1994

Tests of the Parton Model for Inclusive Semileptonic B Decays with the Heavy Quark Effective Theory

In order to study the end-point spectrum of inclusive semileptonic $b \rightarrow u$ decays, we investigate the parton model motivated by deep inelastic scattering process. The reliability of the model is carefully examined by comparing the decay rates and the lepton spectra for $b \rightarrow c$ decay with those of the heavy quark effective theory. We also compute the decay rates of the inclusive semileptonic decay into tau lepton in terms of the parton model, which give another test of the model independently. We conclude that one can make the parton model consistent with the heavy quark effective theory, and it would be phenomenologically useful in extracting $|V_{ub}|$.

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