arXiv subjects

Pyungwon Ko

Publications and source records attributed to Pyungwon Ko.

At least 73 records · Page 4Linked to original sources

arXiv2007

String-derived D4 flavor symmetry and phenomenological implications

In this paper we show how some flavor symmetries may be derived from the heterotic string, when compactified on a 6D orbifold. In the body of the paper we focus on the $D_4$ family symmetry, recently obtained in $Z_3 \times Z_2$ orbifold constructions. We show how this flavor symmetry constrains fermion masses, as well as the soft SUSY breaking mass terms. Flavor symmetry breaking can generate the hierarchy of fermion masses and at the same time the flavor symmetry suppresses large flavor changing neutral current processes.

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arXiv2006

MSSM Anatomy of the Polarization Puzzle in B --> phi K* Decays

We analyze the $B \to ϕK^{*}$ polarization puzzle in the Minimal Supersymmetric Standard Model (MSSM) including the neutral Higgs boson (NHB) contributions. To calculate the non-factorizable contributions to hadronic matrix elements of operators, we have used the QCD factorization framework to the $α_s $ order. It is shown that the recent experimental results of the polarization fractions in $B\to ϕK^{*}$ decays, which are difficult to be explained in SM, could be explained in MSSM if there are flavor non-diagonal squark mass matrix elements of 2nd and 3rd generations, which also satisfy all relevant constraints from known experiments ($B\to X_sγ, B_s\to μ^+μ^-, B\to X_s μ^+μ^-, B\to X_s g, ΔM_s$, etc.). We have shown in details that the experimental results can be accommodated with the flavor non-diagonal mass insertion of chirality RL, RL+LR, RR, or LL+ RR when the NHB contributions as well as $\mathcal{O}(α_s)$ corrections of hadronic matrix elements of operators are included. However the branching ratios for the decay are smaller than the experimental measurements.

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arXiv2005

Partially composite two-Higgs doublet model

In the extra dimensional scenarios with gauge fields in the bulk, the Kaluza-Klein (KK) gauge bosons can induce Nambu-Jona-Lasinio (NJL) type attractive four-fermion interactions, which can break electroweak symmetry dynamically with accompanying composite Higgs fields. We consider a possibility that electroweak symmetry breaking (EWSB) is triggered by both a fundamental Higgs and a composite Higgs arising in a dynamical symmetry breaking mechanism induced by a new strong dynamics. The resulting Higgs sector is a partially composite two-Higgs doublet model with specific boundary conditions on the coupling and mass parameters originating at a compositeness scale $Λ$. The phenomenology of this model is discussed including the collider phenomenology at LHC and ILC.

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arXiv2005

Color-evaporation-model calculation of e^+ e^- -> J/psi+cc-bar+X at root-s=10.6 GeV

Measurements by the Belle Collaboration of the cross section for inclusive J/psi production in e^+e^- annihilation have been a serious challenge to current heavy-quarkonium theory. Especially, the measured cross sections for exclusive J/psi+eta_c and inclusive J/psi+cc-bar+X differ from nonrelativistic QCD predictions by an order of magnitude. In order to check if other available alternative theory can resolve such a large discrepancy, we calculate the cross section for inclusive J/psi+cc-bar+X based on the color-evaporation model. As a phenomenological model, the color-evaporation model is still employed to predict cross sections for inclusive quarkonium production in various processes. Our results show that the color-evaporation-model prediction is even smaller than the nonrelativistic QCD prediction by an order of magnitude. The resultant color-evaporation-model prediction for J/psi+cc-bar+X fraction in the inclusive J/psi production cross section is 0.049, while the empirical value measured by the Belle Collaboration is 0.82.

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arXiv2005

Lepton masses and mixing angles from heterotic orbifold models

We systematically study the possibility for realizing realistic values of lepton mass ratios and mixing angles by using only renormalizable Yukawa couplings derived from heterotic $Z_6$-I orbifold. We assume one pair of up and down sector Higgs fields. We consider both the Dirac neutrino mass scenario and the seesaw scenario with degenerate right-handed majorana neutrino masses. It is found that realistic values of the charged lepton mass ratios, $m_e/m_τ$ and $m_μ/m_τ$, the neutrino mass squared difference ratio, $Δm^2_{31}/Δm^2_{21}$, and the lepton mixing angles can be obtained in certain cases.

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arXiv2005

Inclusive Production of Four Charm Hadrons in e^+ e^- Annihilation at B Factories

Measurements by the Belle Collaboration of the exclusive production of two charmonia in e^+ e^- annihilation differ substantially from theoretical predictions. Till now, no conclusive explanation for this remarkable discrepancy has been provided. Even the origin of the discrepancy is not identified, yet. We suggest that the measurement of four-charm events in Belle data must provide a strong constraint in identifying the origin of this large discrepancy. Our prediction of the cross section for e^+e^- -> c c-bar c c-bar, in lowest order in strong coupling constant, at sqrt{s}=10.6 GeV is about 0.1 pb. If measured four-charm cross section is compatible with the prediction based on perturbative QCD, it is very likely that factorization of hadronization process from perturbative part may be significantly violated or there exists a new production mechanism. If the cross section for the four-charm event is also larger than the prediction like that for the exclusive J/psi+eta_c production, perturbative QCD expansion itself will be proved to be unreliable and loses predictive power.

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arXiv2004

Quark masses and mixing angles in heterotic orbifold models

We study systematically the possibility for realizing realistic values of quark mass ratios $m_c/m_t$ and $m_s/m_b$ and the mixing angle $V_{cb}$ by using only renormalizable Yukawa couplings derived from heterotic orbifold models. We assume one pair of up and down sector Higgs fields. We show realistic examples including hierarchical and democratic forms of Yukawa matrices.

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arXiv1999

Color-octet mechanism in $γ+ p \to J/ψ+ X$

Photoproduction of $J/ψ$ is considered including the color-octet contributions from the various partial wave states, $^{2S+1}L_J$ = $^1S_0$, $^3S_1$ and $^3P_J$. The production cross section depends on three new nonperturbative parameters defined in NRQCD, called the color-octet matrix elements. Using the color-octet matrix elements determined by fitting the $J/ψ$ production at the Tevatron, we find that the color-octet($c\bar{c}) _{8}({^1S_0}~{\rm and~}~{^3P_J})$ contributions to the $J/ψ$ photoproductions at the fixed target experiments and HERA are too large compared to the data on $σ(γ+ p \to J/ψ+X)$ in the forward direction, the $z$ distribution of $J/ψ$. The $P_T^2$ distribution of $J/ψ$ and the total inelastic $J/ψ$ production rate as a function of $\sqrt{s_ {γp}}$ are predicted including color-octet contributions. We also briefly digress on the $B \to J/ψ+ X$ and observe the similar situation. This may be an indication that the color-octet matrix elements determined from the $J/ψ$ production at the Tevatron, especially $<0 | {\cal O}_{8}^ψ ({^1S_0}) | 0>$ and $<0 | {\cal O}_{8}^ψ ({^3P_J}) | 0>$, might have been overestimated by an order of magnitude.

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arXiv1999

Probing SUSY-induced CP violations at B factories

In the minimal supersymmetric standard model (MSSM), the μ-parameter and the trilinear coupling A_t may be generically complex and can affect various observables at B factories. Imposing the edm constraints, we find that there is no new large phase shift in the B^0 - \bar{B^0} mixing, CP violating dilepton asymmetry is smaller than 0.1 %, and the direct CP violation in B\to X_s γcan be as large as \sim \pm 16 %.

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arXiv1999

Effects of supersymmetric CP violating phases on B \to X_s l^+ l^- and ε_K

We consider effects of CP violating phases in μand A_t parameters in the effective supersymmetric standard model on B\to X_s l^+ l^- and ε_K. Scanning over the MSSM parameter space with experimental constraints including edm constraints from Chang-Keung-Pilaftsis (CKP) mechanism, we find that the Br(B\to X_s l^+ l^-) can be enhanced by upto \sim 85 % compared to the standard model (SM) prediction, and its correlation with Br(B \to X_s γ) is distinctly different from the minimal supergravity scenario. Also we find 1 \lesssim ε_K / ε_K^{SM} \lesssim 1.4, and fully supersymmetric CP violation in K_L \to ππis not possible. Namely, |ε_K^{\rm SUSY}| \lesssim O(10^{-5}) if the phases of μand A_t are the sole origin of CP violation.

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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

B decays into two light pseudoscalar mesons and possible effects of enhanced b --> s g

We consider the branching ratios and CP asymmetry in the B meson decays into two pseudoscalar mesons in the generalized factorization approximation. We also investigate the possible effects of the enhanced chromomagnetic interaction b --> s g on these exclusive B meson decays that was suggested as a possible solution to the semileptonic branching ratio of B mesons, the missing charm puzzle and the large B --> η^{'} + X_s. We finds that such enhanced b --> s g interaction degrades the agreement between the data and the model predictions for B meson decays into two light mesons in the generalized factorization approximation.

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arXiv1998

Mass Matrix Ansatz for Degenerate Neutrinos Consistent with Solar and Atmospheric neutrino Data

We suggest mass matrices for neutrinos and charged leptons that can explain solar and atmospheric neutrino data. The resulting flavor mixing matrix $V_ν$ has a property that $(V_ν)_{13}=0$, thus making $ν_e \leftrightarrow ν_μ$ and $ν_μ \leftrightarrow ν_τ$ oscillations to be effectively a two-channel problem. Phenomenological consequences of the lepton mass matrix ansatze are consistent with the current data on various type of neutrino oscillation experiments except the LSND measurement. %and that three neutrinos are almost degenerate in mass. Three neutrinos, being almost degenerate with $\sum | m_{ν_i} | \lesssim 1 $ eV, can be a part of hot dark matter without any conflict with the constraint from neutrinoless double beta decay experiments. The $ν_μ \leftrightarrow ν_τ$ oscillation, $\sin^2{2θ_{μτ}}$, is predicted to be 0.86-0.97 with $Δm^2_{μτ}\simeq 2 \times 10^{-3} {eV}^2$, which is consistent with the atmospheric neutrino data and can be tested further at the planned MINOS and K2K experiments searching for $ν_μ \to ν_τ$ oscillation.

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arXiv1998

A new method for extracting the weak phase gamma from B ---> D K(*) decays

A new method to extract the weak phase $γ$ is suggested by exploiting B ---> D K^{(*)} decay modes that are not Cabibbo suppressed, using the isospin relations, and ignoring the annihilation diagram as usual. Assuming $3 \times 10^8 B\bar{B}$ pair at $B$ factories, one can determine $γ$ with $3-σ$ accuracy for 80^o < $γ$ < 150^o using B ---> D K modes and for 50^o < $γ$ < 170^o using B ---> D K^* modes.

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arXiv1998

Recent Developments In Heavy Quarkonium Physics

Recent developments in heavy quarknoium physics are reviewed in brief, including (i) nonrelativistic QCD(NRQCD), (ii) the importance of color-octet $(Q\bar{Q})$ components in the decay and the production of a physical heavy quarkonium state, (iii) limitation of the NRQCD factorization and (iv) the double humps in the $ππ$ spectrum in the decay $Υ(3S) \to Υ(1S) ππ$.

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arXiv1997

More on R-parity and lepton-family number violating couplings from muon(ium) conversion, and τand $π^0$ decays

We present a new class of constraints to the lepton-family number and R-parity violating couplings from muonium conversion, $μ^{-} + {_{22}^{48}} Ti \to e^{-} + {_{22}^{48}} Ti$, a class of tau decays, $τ\to l +$ (light meson) with $l= μor e$, and $J/ψ$ and $π^0$ decays into a lepton pair. We find that $μ^{-} + {_{22}^{48}} Ti \to e^- + {_{22}^{48}} Ti$ provides one of the strongest constraints along with $Δm_{K}, Δm_{B}$, $μ\to e γ$ and the neutrinoless double $β$ decay. Search for these lepton-family number violating (LFNV) decays forbidden in the standard model is clearly warranted in various low-energy experiments such as Tau-Charm Factories and PSI, etc.

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arXiv1997

Color-octet mechanism in the inclusive D-wave charmonium productions in B decays

The inclusive D-wave charmonium production rates in B decays are considered in the Bodwin-Braaten-Lepage (BBL) approach. We find that the color-octet subprocesses B->cc_(^3S_1^(8) or ^3P_J^(8))+s,d, followed by the transition cc_(^3S_1^(8) or ^3P_J^(8)) -> ^3D_J, strongly dominate over any other subprocess, due to the large Wilson coefficient for the ΔB = 1 effective lagrangian. Assuming that the numerical values of the matrix elements <0|O^{^3D_J}(^3S_1^(8))|0> and <0|O^{^3D_J}(^3P_J^(8))|0> are the same order of magnitudes with the <0| O^{ψ^'}(^3S_1^(8))|0>, we find that the ^{1,3}D_{2} can be observed at future B-factories.

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arXiv1996

Almost maximally broken permutation symmetry for neutrino mass matrix

Assuming three light neutrinos are Majorana particles, we propose mass matrix ansatz for the charged leptons and Majorana neutrinos with family symmetry $S_{3} $ broken into $S_{1}$ and $S_{2}$, respectively. Each matrix has three parameters, which are fixed by measured charged lepton masses, differences of squared neutrino masses relevant to the solar and the atmospheric neutrino puzzles, and the masses of three light Majorana neutrinos as a candidate for hot dark matter with $\sum |m_ν| \sim 6 eV$. The resulting neutrino mixing is compatible with the data for the current upper limit, $ < m_{ν_e} >_{th} < 0.8 eV$, of neutrino-less double beta decay experiments, and the current data for various types of neutrino oscillation experiments. One solution of our model predicts that $ν_μ \rightarrow ν_τ$ oscillation probability is about $< 0.008$ with $Δm^{2} \sim 10^{-2} eV^2$, which may not be accessible at CHORUS and other ongoing experiments.

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