arXiv subjects

Pyungwon Ko

Publications and source records attributed to Pyungwon Ko.

83 records · Page 5Linked to original sources

arXiv1996

A simple modification of the maximal mixing scenario for three light neutrinos

We suggest a simple modification of the maximal mixing scenario (with $S_3$ permutation symmetry) for three light neutrinos. Our neutrino mass matrix has smaller permutation symmetry $S_{2}$ ($ν_μ \leftrightarrow ν_{e}$), and is consistent with all neutrino experiments except the $^{37}$Cl experiment. The resulting mass eigenvalues for three neutrinos are $m_{1} \approx (2.55-1.27) \times 10^{-3} eV, m_{2,3} \approx (0.71-1.43) eV$ for $Δm_{LSND}^{2} = 0.5 - 2.0 eV^2$. Then these light neutrinos can account for $\sim (2.4-4.8)% (6.2-12.4 %)$ of the dark matter for $h = 0.8 (0.5)$. Our model predicts the $ν_μ \rightarrow ν_τ$ oscillation probability in the range sensitive to the future experiments such as CHORUS and NOMAD.

hep-ph↗

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

Chiral perturbation theory vs. vector meson dominance in the decays $ϕ\to ργγ$ and $ϕ\to ωγγ$

It is pointed out that the radiative decays of a $ϕ$ meson, $\phirho$ and $\phiom$, receive dominant contributions from the pseudoscalar ($P = η, η^{'}$) exchanges. Using the vector meson dominance model, we find that $B (\phirho) \approx 1.3 \times 10^{-4}$ and $B (\phiom) \approx 1.5 \times 10^{-5}$, which are mainly from the $η^{'}$ pole. Thus, these decays are well within the reach of the $ϕ$ factory. Our estimates are a few orders of magnitude larger than the chiral loop contributions in the heavy vector meson chiral lagrangian, which is about ( a few ) $\times 10^{-9}$.

hep-ph↗

arXiv1995

Inclusive $S-$wave charmonium productions in $B$ decays

The inclusive $S-$wave charmonium production rates in $B$ decays are considered using the Bodwin-Braaten-Lepage (BBL) approach, including the relativistic corrections and the color-octet mechanism suggested as a possible solution to the $ψ^{'}$ puzzle at the Tevatron. We first consider relativistic and radiative corrections to $J/ψ\rightarrow e^{+} e^{-}$ and $J/ψ\rightarrow$ Light Hadrons (LH), in order to determine two nonperturbative parameters, $\langle J/ψ| O_{1} (^{3}S_{1}) | J/ψ\rangle$, $\langle J/ψ| P_{1} (^{3}S_{1}) | J/ψ\rangle$, in the factorization formulae for these decays. Using these two matrix elements and including the color-octet $c\bar{c}(^{3}S_{1})$ state contribution, we get a moderate increase in the decay rates for $B$ decays into $J/ψ~({\rm or}~ψ^{'}) ~+ X$. Our results, $B(B \rightarrow J/ψ~({\rm or}~ψ^{'}) + X) = 0.58~(0.23) \%$ for $M_{b} = 5.3$ GeV, get closer to the recent CLEO data. As a byproduct, we prefer a larger decay rate for $η_{c} \rightarrow$ LH compared to the present data.

hep-ph↗

arXiv1995

$η\to π^{0} γγ$ and $γγ\to π^{0} π^{0}$ in $O(p^{6})$ chiral perturbation theory

$η\rightarrow π^{0} γγ$ and $\ggpipi$ are considered in $O(p^{6})$ chiral perturbation theory. In addition to the usual $ρ,ω$ contributions, there are two $O(p^{6})$ operators (${\cal L}_{6,m}$) arising from explicit chiral symmetry breaking. Since only one of the two operators contributes to $\etapigg$, the coefficient of this operator ($\equiv d_3$) can be determined in two ways : (i) from the measured decay rate of $η\rightarrow π^{0} γγ$, and (ii) by assuming the resonance saturations of the low energy coefficients in the $O(p^{6})$ chiral lagrangian. We find that two methods lead to vastly different values of $d_3$, which would indicate that either the measured decay rate for $η\rightarrow π^{0} γγ$ is too large by a factor of $2 \sim 3$, or the resonance saturation assumptions do not work for $d_3$.

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↗

arXiv1994

New Approach for Measuring $|V_{ub}|$ at Future $B$-Factories

It is suggested that the measurements of hadronic invariant mass ($m_X$) distributons in the inclusive $B \rightarrow X_{c(u)} l ν$ decays can be useful in extracting the CKM matrix element $|V_{ub}|$. We investigated hadronic invariant mass distributions within the various theoretical models of HQET, FAC and chiral lagrangian as well as ACCMM model. It is also emphasized that the $m_X$ distribution even at the region $m_{X} > m_{D}$ in the inclusive $b\rightarrow u$ are effetive in selecting the events, experimentally viable at the future asymmetric $B$ factories, with better theoretical understandings.

hep-ph↗

arXiv1994

Measuring $|V_{ub}|$ at future B-Factories

We calculate the so--called Fermi motion parameter $p_{_F}$ of ACCMM model using the variational method in a potential model approach. We also propose hadronic invariant mass distribution as an alternative experimental observable to measure $V_{ub}$ at future asymmetric $B$ factories.

hep-ph↗

arXiv1993

Final-state ππinteractions in Υ(3S)\rightarrowΥ(1S)ππ

The $m_{ππ}$ spectrum and various angular distributions in $\upss$ are studied including the effects of the $ππ$ phase shift in the $I=L=0$ channel using the lowest order amplitude in the pion momentum expansion. Our results are compared with the recent CLEO data, and we find good agreement except for the $\cosθ_π^*$ distributions. We argue that the $\cosθ_π^*$ distribution, contrary to other distributions, is sensitive to the higher order corrections in the pion momentum expansion. This argument is supported by using an ansatz for the amplitude which is of higher order in the pion momentum expansion and still satisfies the soft pion theorem.

hep-ph↗

arXiv1993

Schrödinger Fields on the Plane with $[U(1)]^N$ Chern-Simons Interactions and Generalized Self-dual Solitons

A general non-relativistic field theory on the plane with couplings to an arbitrary number of abelian Chern-Simons gauge fields is considered. Elementary excitations of the system are shown to exhibit fractional and mutual statistics. We identify the self-dual systems for which certain classical and quantal aspects of the theory can be studied in a much simplified mathematical setting. Then, specializing to the general self-dual system with two Chern-Simons gauge fields (and non-vanishing mutual statistics parameter), we present a systematic analysis for the static vortexlike classical solutions, with or without uniform background magnetic field. Relativistic generalizations are also discussed briefly.

hep-th↗

arXiv1993

Is Upsilon(3S) a pure S-wave?

Assuming the QCD multipole expansion is applicable to hadronic transitions of Upsilon(3S) into lower level bottomonia, we consider the possibility that Upsilon(3S) has a D-wave component. This assumption leads to a natural explanation of the pi-pi spectrum in Upsilon(3S) -> Upsilon(1S) pi-pi. Consequences of this assumption on other hadronic and radiative transitions of Upsilon(3S) are also discussed in the same context.

hep-ph↗