Global aspects of the scalar meson puzzle

A generalized linear sigma model for low energy QCD is employed to study the quark structure of eight low lying scalar isomultiplets as well as eight low lying pseudoscalar isomultiplets. The model, building on earlier work, assumes the possible mixing of quark anti-quark states with others made of two quarks and two antiquarks. No {\it a priori} assumption is made about the quark contents of the states, which emerge as predictions. An amusing and contrasting pattern for the quark structure is found; the lighter conventional pseudoscalars are, as expected, primarily of two quark type whereas the lighter scalars have very large four quark admixtures. The new feature of the present paper compared to earlier ones in this series involves the somewhat subtle and complicated effects of SU(3) flavor breaking. They do not alter the general pattern of two quark vs. four quark mixing obtained in the SU(3)symmetric case but, of course, give a more detailed picture

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 Puzzle in QCD

An approach to understanding the light scalar meson phenomenology is briefly reviewed.Comment: Talk at XII Mexican Workshop on Particles and Fields, 5-14 Nov. 2009, Mazatlan, Mexic

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

Model for light scalars in QCD

We propose a systematic procedure to study a generalized linear sigma model which can give a physical picture of possible mixing between $q{\bar q}$ and $qq{\bar q}{\bar q}$ low lying spin zero states. In the limit of zero quark masses, we derive the model independent results for the properties of the Nambu Goldstone pseudoscalar particles. For getting information on the scalars it is necessary to make a specific choice of terms. We impose two plausible physical criteria - the modeling of the axial anomaly and the suppression of effective vertices representing too many fermion lines - for limiting the large number of terms which are allowed on general grounds. We calculate the tree-level spectrum based on the leading terms in our approach and find that it prominently exhibits a very low mass isosinglet scalar state. Finally we point out that the low energy result for scattering of pions continues to hold in the general version of the model.Comment: 4 pages, 1 figur