Searcharxiv⌕ Search

arXiv subjects

C. S. Kim

Publications and source records attributed to C. S. Kim.

At least 217 records · Page 12Linked to original sources
arXiv2000

A Systematic Analysis of the Exclusive B -> K^* l^+ l^- Decay

A model-independent analysis for the exclusive, rare B -> K^* l^+ l^- decay is presented. Systematically studied are the experimentally measured quantities, such as, branching ratio, forward-backward asymmetry, longitudinal polarization of the final leptons, and the ratio $Γ_L/Γ_T$ of the decay widths when $K^\ast$ meson is longitudinally and transversally polarized. The dependence of the asymmetry parameter $α= 2 Γ_L/Γ_T -1$ on the new Wilson coefficients is also studied in detail. It is found that the afore-mentioned physical observables are quite sensitive to the new Wilson coefficients. Therefore, once we have the experimental data with high statistics and a deviation from the Standard Model, we can interpret the source of such discrepancy.

hep-ph↗
arXiv1999

Search for New Physics in the Semileptonic D_{l4} Decays, D->K πl ν

New physics effects through the direct CP violation and the decay rate change are investigated in the semileptonic $D_{l4}$ decays, $D^\pm\to Kπl^\pm ν$, by including a scalar-exchange interaction with a complex coupling. In the decay process, we included various excited states as intermediate states decaying to the final hadrons, $K+π$, and found that among the intermediate states only the lowest state ($K^*$) is dominant and the other higher excited states are negligible, contrary to the $B_{l4}$ decays. We also obtained constraints on the new complex coupling within the multi-Higgs doublet model and the scalar leptoquark models.

hep-ph↗
arXiv1999

$b \to s γ$ decays in the Left-Right Symmetric Model

We consider $b \to s γ$ decays in the Left-Right Symmetric Model. Values of observables sensitive to chiral structure such as the $Λ$ polarization in the $Λ_b \to Λγ$ decays and the mixing-induced CP asymmetries in the $B_{d,s} \to M^0 γ$ decays can deviate in the LRSM significantly from the SM values. The combined analysis of $P_Λ$ and $A_{CP}$ as well as ${\cal BR}(b \to s γ)$ can be used to determine the model parameters.

hep-ph↗
arXiv1999

A Systematic Analysis of the Lepton Polarization Asymmetries in the Rare B Decay, B -> X_sτ^+τ^-

The most general model-independent analysis of the lepton polarization asymmetries in the rare B decay, $\Bstt$, is presented. We present the longitudinal, normal and transverse polarization asymmetries for the $τ^+ $ and $τ^-$, and combinations of them, as functions of the Wilson coefficients of twelve independent four-Fermi interactions, ten of them local and two nonlocal. These procedures will tell us which type of operators contributes to the process. And it will be very useful to pin down new physics systematically, once we have the experimental data with high statistics and a deviation from the Standard Model is found.

hep-ph↗
arXiv1999

Hierarchical Quark Mixing and Bimaximal Lepton Mixing on the Same Footing

We show that not only the hierarchical quark CKM mixing matrix but also the "bimaximal" lepton flavor mixing matrix can be derived from the same mass matrix ansatz based on the broken permutation symmetry, by assuming the hierarchy of neutrino masses to be $m_1\simeq m_2 <<m_3$. We also reproduce the recently measured angle of unitary triangle, $\sin 2β$, as well as all the observed experimental values of $V_{\tiny CKM}$ of the quark CKM matrix. And we predict Jarlskog rephasing invariant quantity, $J_{\tiny CP} \simeq 0.18 \times 10^{-4}$, and the upper bound of the same quantity in the lepton sector, $J^l_{\tiny CP} \leq 0.012$, which may be indeed large enough to generate the lepton number violation of the universe.

hep-ph↗
arXiv1999

CP Violation in the Semileptonic B_{l4} (B^\pm -> pi^+ π^- l^\pm ν) Decays

Direct CP violations in $B_{l4}$ decays ($B^\pm \to π^+π^- l^\pm ν_l$) are investigated within the Standard Model (SM) and also in its extensions. In the decay processes, we include various excited states as intermediate states decaying to the final hadrons, $π^+ + π^-$. The CP violation within the SM is induced by the interferences between intermediate resonances with different quark flavors. As extensions of the SM, we consider CP violations implemented through complex scalar-fermion couplings in the multi-Higgs doublet model and the scalar-leptoquark models. We calculate the CP-odd rate asymmetry and the optimal asymmetry. We find that the optimal asymmetry can be measured at $1σ$ level with about $10^9$ $B$-meson pairs in the SM case and $10^3$--$10^7$ pairs in the extended model case, for maximally-allowed values of CP-odd parameters in each case.

hep-ph↗
arXiv1999

Heavy Majorana neutrinos in e+e- colliders

We investigate possibilities for detecting heavy Majorana neutrinos ($N$'s) in $e^+e^-$ at LEP200 and future Linear Colliders. We concentrate on the processes where the pairs of intermediate heavy $N$'s produce a clear signal of total lepton number violation ($e^+e^- \to NN \to W^+l^-W^+l^{\prime -}$). Such a signal is not possible if the heavy neutrinos are of Dirac nature. Our approach is general in the sense that the intermediate $N$'s can be either on shell or off shell. Discussion of the relative numerical importance of the $s$ and the $t+u$ channels of the $NN$ production is also included.

hep-ph↗
arXiv1999

New Physics Effects in $B \to K^(*) νν$ Decays

We present a model-independent analysis of rare B decays, $B \to K^{(*)} νν$. The effect of possible new physics is written in terms of dimension-6 four-fermi interactions. The lepton number violating scalar- and tensor-type interactions are included, and they induce $B \to K^{(*)} νν({\bar ν} {\bar ν})$ decays. We show systematically how the branching ratios and missing mass-squared spectrum depend on the coefficients of the four-fermi interactions.

hep-ph↗
arXiv1999

Searching for New Physics in the b->d FCNC using B_s^0(t)->ϕK_s and B_d^0(t)->K^0\bar{K}^0

Time-dependent measurements of the decays B_s^0(t)-->ϕK_s and B_d^0(t) --> K^0 \bar{K}^0 can be used to compare the weak phases of B_d^0-\bar{B}_d^0 mixing and the t-quark contribution to the b->d penguin. Since these two phases are equal in the standard model, any discrepancy would be a sign of new physics, specifically in the b->d flavour-changing neutral current (FCNC). The method can be applied to other pairs of decays, such as B_s^0(t)--> J/ΨK_s and B_d^0(t)--> J/Ψπ^0.

hep-ph↗
arXiv1998

Bi-maximal Lepton Flavor Mixing Matrix and Neutrino Oscillation

Recently, many authors showed that if the solar and atmospheric neutrino data are both described by maximal mixing vacuum oscillations at the relevant mass scale, then there exists a unique bi-maximal lepton mixing matrix for three neutrino flavors. We construct the lepton mass matrices from the symmetry principle so that maximal mixings for the atmospheric and the solar neutrino vacuum oscillations are naturally generated. Although the hierarchical patterns of the lepton sector are quite different from each other, we show how two different mass matrices suggested in this work can be generated in a unified way. We also give comments on possible future tests of the bi-maximal lepton mixing matrix.

hep-ph↗
arXiv1998

CP Violation in the Semileptonic $B_{l4}$ (B->D πl ν) Decays: A Model Independent Analysis

CP violation from physics beyond the Standard Model is investigated in $B_{l4}$ decays: $B\to Dπl\barν_l$. The semileptonic $B$-meson decay to a $D$-meson with an emission of single pion is analyzed with heavy quark effective theory and chiral perturbation theory. In the decay process, we include various excited states as intermediate states decaying to the final hadrons, $D+π$. The CP violation is implemented in a model independent way, in which we extend leptonic current by including complex couplings of the scalar sector and those of the vector sector in extensions of the Standard Model. With these complex couplings, we calculate the CP-odd rate asymmetry and the optimal asymmetry. We find that the optimal asymmetry is sizable and can be detected at $1σ$ level with about $10^6$-$10^7$ $B$-meson pairs, for some reference values of new physics effects.

hep-ph↗
arXiv1998

CP Violation in the Semileptonic $B_{l4}$ ($B->D πl ν$) Decays: Multi-Higgs Doublet Model and Scalar-Leptoquark Models

CP violation from physics beyond the Standard Model is investigated in $B_{l4}$ decays: $B\to Dπl\barν_l$. In the decay process, we include various excited states as intermediate states decaying to the final hadrons, $D+π$. We consider the semileptonic decay to a tau lepton family as well. The CP violation is implemented through complex scalar--fermion couplings in the multi-Higgs doublet model and scalar-leptoquark models beyond the Standard Model. With these complex couplings, we calculate the CP-odd rate asymmetry and the optimal asymmetry. We find that for $B_{τ4}$ decays the optimal asymmetry is sizable and can be detected at $1σ$ level with about $10^6$-$10^7$ $B$-meson pairs, for maximally-allowed values of CP-odd parameters in those extended models.

hep-ph↗
arXiv1998

Higgs-mediated flavor-changing neutral currents in the general framework with two Higgs doublets -- an RGE analysis

We consider the standard model with two Higgs doublets with the most general Yukawa coupling terms (``type III''). In the model, the neutral-Higgs-mediated flavor-changing neutral currents (FCNC's) are allowed, but must be reasonably suppressed at low energies of probes. It has been known that the existing hierarchies of quark masses render this suppression at low energies rather natural. On the other hand, the model has been regarded by many as unnatural because of the absence of any symmetry that would ensure persistence of this suppression as the energy of probes increases. The opinion has been based on the expectation that the mentioned FCNC's would increase by large factors at increasing energies. We performed a numerical analysis of the flow of these FCN coupling parameters as governed by the one-loop renormalization group equations (RGE's), in a simplified case when Yukawa couplings of the first quark generation are neglected. The analysis shows a remarkable persistence of the mentioned FCNC suppression and thus indicates that the model is not unnatural in the RGE sense. Further, we point out two mistakes in the Yukawa RGE's of Machacek and Vaughn at one-loop level.

hep-ph↗
arXiv1998

Exclusive B --> M l^+ l^- (M=π, K, ρ, K^*) Decays and Determinations of |V_{ts}| (and |V_{td}/V_{ts}|)

We examine the possibility for precise determination of |V_{ts}| (and |V_{td}/V_{ts}|) from the exclusive decays, $B --> K \ell^+ \ell^-, B --> K^* \ell^+ \ell^-$ (and $B --> π\ell^+ \ell^-, B --> ρ\ell^+ \ell^-$). We show that the ratio |V_{ts}| can be extracted experimentally with a small theoretical uncertainty from hadronic form--factors, if we {\bf appropriately constrain} kinematical regions of $q^2$. We also give detailed analytical and numerical results on the differential decay width $dΓ(B --> K^* \ell^+ \ell^-)/dq^2$, and the ratios of integrated branching fractions, ${\cal B}(B --> ρ\ell^+ \ell^-)/{\cal B}(B --> K^* \ell^+ \ell^-)$. We estimate that one can determine the ratio |V_{ts}| from those decays within theoretical accuracy of $\sim 10%$.

hep-ph↗
arXiv1998

Neutrino Oscillations and Lepton Flavor Mixing

In view of the recent announcement on non-zero neutrino mass from Super-Kamiokande experiment, it would be very timely to investigate all the possible scenarios on masses and mixings of light neutrinos. Recently suggested mass matrix texture for the quark CKM mixing, which can be originated from the family permutation symmetry and its suitable breakings, is assumed for the neutrino mass matrix and determined by the four combinations of solar, atmospheric and LSND neutrino data and cosmological hot dark matter bound as input constraints. The charged-lepton mass matrix is assumed to be diagonal so that the neutrino mixing matrix can be identified directly as the lepton flavor mixing matrix and no CP invariance violation originates from the leptonic sector. The results favor hierarchical patterns for the neutrino masses, which follow from the case when either solar-atmospheric data or solar-HDM constraints are used.

hep-ph↗
arXiv1998

A Model Independent Analysis of the Rare B Decay B -> X_s l^+ l^-

The most general model-independent analysis of the rare $B$ decay, $\Bsll$, is presented. There are ten independent local four-Fermi interactions which may contribute to this process. The branching ratio, the forward-backward asymmetry, and the double differential rate are written as functions of the Wilson coefficients of the ten operators. We also study the correlation between the branching ratio and the forward-backward asymmetry by changing each coefficient. This procedure tells us which types of operator contribute to the process, and it will be very useful to pin down new physics systematically, once we have the experimental data with high statistics and the deviation from the Standard Model is found.

hep-ph↗
arXiv1998

A New Mechanism for $B^{\pm}\to η'K^{\pm}$ in Perturbative QCD

We present a new mechanism for $B^{\pm}\to η' K^{\pm}$, and analyze it strictly within perturbative QCD. We find that such a new mechanism may dominate non-leptonic $B$-decays to light mesons. Within a reasonable parameter space, our prediction is in good agreement with the recent CLEO data on $B^{\pm}\to η' K^{\pm}$. We conclude that there is no room for an abnormally large \bsg vertex from physics beyond the Standard Model.

hep-ph↗