Special Nuclear Theory Seminar

Unlike the light pseudoscalar mesons, understanding the properties of light scalar mesons (particularly, their quark substructure) is known to be quite nontrivial.
Scalar mesons are important from the theoretical point of view because they are effectively the Higgs bosons of QCD and induce chiral symmetry breaking, and therefore, are probes of the QCD vacuum. Scalars are also important from a phenomenological point of view, as they are crucial intermediate states in Goldstone boson interactions away from threshold; in a range of energy that is too high for a chiral perturbation theory framework, and too low in the context of the perturbative QCD. The physics of scalar mesons has a
great impact on our understanding of important issues in strong interactions such as the diquarks, glueballs, hybrids, violation of isospin, low energy hadron phenomenology,
instantons, and final-state interaction of pseudoscalar mesons. Moreover, physics of scalar mesons can provide significant insights outside its immediate focus of low-energy QCD such as, for example, in studies of decay Ds to f0(980) e+ ve or decay Bs to J/psi f0(980) measured by LHCb.


In this talk, the status of the scalar mesons will be briefly reviewed and the generalized linear sigma model of low-energy QCD for understanding their properties will be presented. Specifically, the underlying symmetries (and their breakdown) for designing the generalized linear sigma model, as well as various contacts with experiment for fixing the free paremeters of the model will be discussed in some details. Several predictions for various low-energy processes as well as the application of this model to studies of heavier meson decays will be given, and directions for further extensions of the model will be discussed.