Related papers: Does the light and broad sigma(500) exist?
The lightest scalar and pseudoscalar nonets are discussed within the [A framework of the broken old UxU3 linear sigma model, and it is shown that already at the tree level this model works remarkably well predicting scalar masses and…
My recent fit of the light scalar mesons is discussed in the light of the U3 x U3 linear sigma model. The argument for why there exists a light and broad sigma meson is explained in more detail, and the mechanism of spontaneous symmetry…
This report summarizes the most important results presented at the recent conference held at the Yukawa Institute of Theoretical Physics in Kyoto, devoted to the recently confirmed light sigma resonance. Remarkably, all speakers at this…
First I review some previous work on the lightest scalars below 1.5 GeV, and how these scalars can be understood as unitarized nonet states. The bare scalars are strongly distorted by hadronic mass shifts, and the lightest I=0 state becomes…
The light scalar meson sigma(600) is known to appear at low excitation energy with very large width on top of continuum states. We investigate it in the QCD sum rule as an example of resonance structures appearing above the corresponding…
We discuss the classification of the light scalar mesons with mass below 2 GeV into q qbar nonets and glueballs. The information on production and decay of these states, in particular recent information on f_0(980), f_0(400-1200) (or…
The linear sigma model with broken U3xU3 is compared with data on the lightest scalar and pseudoscalar mesons. When 5 of the 6 parameters are fixed by the pseudoscalar masses and decay constants one finds that, already at the tree level, a…
From recent analysis of the $\pi\pi$ scattering amplitude, it has been claimed that there exists a broad and light $\sigma$ meson. However, if this meson really exists, it must also appear in other observables such as the pion scalar form…
A multichannel description of the light scalar mesons in the framework of the Resonance-Spectrum Expansion is generalised by including vector-vector and scalar-scalar channels, besides the usual pseudoscalar-pseudoscalar channels.…
In the light scalar meson sector (M < 1.8 GeV) one expects at least one q qbar nonet and a glueball, possibly also multi-quark states. We discuss the present phenomenological evidence for sigma and kappa particles; if real, they could be…
We discuss how the lightest scalars, in particular the broad sigma resonance, can be understood as unitarized (qbar q) states within a unitarized quark model (UQM). The bare (qbar q) scalars are strongly distorted by hadronic mass shifts,…
Within a linear sigma model framework, possible mixing between two chiral nonets (a two quark nonet, and a four quark nonet) below 2 GeV is studied. Incorporating the U(1)$_A$ behavior of the underlying QCD, and working in the isospin…
We enforce chiral Ward identities on the vertices of the linear sigma model to take into account the width of the scalar sigma, considered as a true physical resonance. We consider pion scattering at very low energies and, from a fit to the…
In this talk I briefly review the recent developments on light scalar meson spectroscopy, paying particular attention to the causes of major revision of the $\sigma$ or $f_0(500)$ meson in the Review of Particle Phsycis. This resonance,…
We discuss how the a_0(980), f_0(980), K^*_0(1430) and particularly the broad sigma resonance can be understood within a coupled channel framework, which includes all light two-pseudoscalar thresholds together with constraints from Adler…
This talk is a brief account of recent developments on light scalar meson spectroscopy. I mostly focus on the major revision of the $\sigma$ or $f_0(500)$ meson in the Review of Particle Physics, driven by new data and the accummulation of…
Whether the $\sigma-meson$ ($f_0(600)$) exists as a real particle is a long-standing problem in both particle physics and nuclear physics. In this work, we analyze the deuteron binding energy in the linear $\sigma$ model and by fitting the…
I discuss how an extra light scalar meson multiplet could be understood as an effective Higgs nonet of a hidden local U(3) symmetry. There is growing evidence that low energy data requires in addition to a conventional (q bar q) nonet near…
We show that the presence of a lightish scalar resonance, $\sigma$, that mixes with the composite Goldstone-Higgs boson can relax the typical bounds found in this class of models. This mechanism, inbred in models with a walking dynamics…
We formulate an extended linear $\sigma$ model of a quarkonia nonet and a tetraquark nonet as well as a complex iso-singlet (glueball) by virtue of chiral symmetry $SU_L(3) \times SU_R(3)$ and $U_A(1)$ symmetry. In the linear realization…