Study of scalar mesons in chiral Lagrangian frameworks

We review two approaches to studying pseudoscalar meson-meson scattering amplitudes to beyond 1 GeV using non-linear and linear chiral Lagrangians. These approaches use two different unitarisation techniques - a generalised Breit Wigner prescription and K-matrix unitarization respectively. We also report some preliminary findings on K-matrix unitarisation of the I=J=0 pion-pion scattering amplitude in the non-linear chiral Lagrangian approach and make some remarks about the light scalar mesons.Comment: Contribution to XII Conference on Hadron Spectroscopy, Frascati 2007. 8 pages, 2 figure

Two or Four: A Hint from Scalar Mesons in Radiative phi Decays ?

In this write-up, we summarize our recent analysis of radiative decays involving light scalar mesons. Our analysis using the vector meson dominance model at tree level indicates that it may be difficult to distinguish $qq\bar{q}\bar{q}$ picture and $q\bar{q}$ picture for the light scalar nonet. Our result on the process of $\phi \to \pi^0 \eta \gamma$ shows that the derivative-type $f_0 K\bar{K}$ interaction reproduces experimental data below 950 GeV well, but gives a poor fit above 950 GeV, i.e., in the energy region around the mass of $a_0(980)$, but that the discrepancy can be compensated by the effect of the $K$ loop.Comment: Talk given by M. Harada at Yukawa International Seminar (YKIS) 2006 ``New Frontiers in QCD -Exotic Hadrons and Hadronic Matter-'

Vector Meson Dominance Model for Radiative Decays Involving Light Scalar Mesons

We study a vector dominance model which predicts a fairly large number of currently interesting decay amplitudes of the types S -> \gamma \gamma, V -> S \gamma and S -> V \gamma, where S and V denote scalar and vector mesons, in terms of three parameters. As an application, the model makes it easy to study in detail a recent proposal to boost the ratio Gamma(phi -> f_0 gamma) / Gamma(phi -> a_0 gamma) by including the isospin violating a_0 - f_0 mixing. However we find that this effect is actually small in our model.Comment: 4 pages, 1 figure, REVTeX. Table I and paragraph on application of model to study effect of a_0 - f_0 mixing revise

Radiative Decays involving a0(980) and f0(980) in the Vector Meson Dominance Model

We summarize some features of the vector meson dominance model which was recently proposed for studying radiative decays involving the scalar mesons. Using the experimental values of $\Gamma(a_0 \to \gamma\gamma)$, $\Gamma(f_0 \to \gamma\gamma)$ and $\Gamma(\phi \to a_0 \gamma)$ as inputs, we show that the model predicts a large hierarchy between $\Gamma(a_0 \to \omega \gamma)$ and $\Gamma(a_0 \to \rho \gamma)$ as well as between $\Gamma(f_0 \to \omega \gamma)$ and $\Gamma(f_0 \to \rho \gamma)$.Comment: 7pages, Talk given by M. Harada at International Symposium on Hadron Spectroscopy, Chiral Symmetry and Relativistic Description of Bound Systems, February 24-26, 2003, Nihon University, Tokyo, Japa

Exploring the structure of a possible light scalar nonet

We first review the work of the Syracuse group, which uses an effective chiral Lagrangian approach, on meson-meson scattering. An illustration providing evidence for the existence of a strange scalar resonance of mass around 900 MeV is given. An attempt to fit this $\kappa (900)$ together with a similarly obtained $\sigma (560)$ and the well known $a_0(980)$ and $f_0(980)$ into a nonet pattern suggests that the underlying structure is closer to a dual quark-dual antiquark than to a quark-antiquark. A possible mechanism to explain a next higher-in mass scalar meson nonet is also discussed. This involves mixing between $q{\bar q}$ and $qq{\bar q} {\bar q}$ states.Comment: 8 pages, 4 figures, invited talk at workshop "Possible Existence of the Light Sigma Resonance and its Implications to Hadron Physics", Yukawa Institute for Theoretical Physics, Kyoto, Japan, June 200

Light Scalar Mesons

We review how a certain effective chiral Lagrangian approach to pi pi scattering, pi K scattering and eta-prime decay to eta pi pi provides evidence for the existence of light scalars sigma(550) and kappa(900) as well as describing the f0(980) and the a0(980). An attempt to fit these into a nonet suggests that their structure is closer to a dual quark-dual antiquark than to a quark-antiquark. A possible mechanism to explain the next higher mass scalar nonet is also proposed.Comment: 10 pages, 4 figures, talk given at Hadron Physics: Effective Theories of Low Energy QCD, Coimbra, Portugal, Sept. 199

Tau-Mu Flavor Violation and the Scale of New Physics

Motivated by the strong experimental evidence of large nu_mu - nu_tau neutrino oscillations, we study existing constraints for related mu - tau flavor violation. Using a general bottom-up approach, we construct dimension-6 effective fermionic operators whose coefficients encode the scale of new physics associated with mu - tau flavor violation, which is a piece in the puzzle of the origin of neutrino oscillations. We survey existing experimental bounds on this scale, which arise mostly from tau and B decays. In many cases the new physics scale is constrained to be above a few TeV. We also discuss the operators which are either weakly constrained or, at present, subject to no experimental bounds.Comment: Proceedings for MRST 2003, Joe Schechter Fest, Syracuse University, New York, May 2003. 8 pages, 2 figure