On the low energy end of the QCD spectrum
arXiv:0809.5053 · doi:10.1016/j.nuclphysbps.2008.12.076
Abstract
The energy gap of QCD is now understood very well. There is no doubt that the expansion in powers of the two lightest quark masses does represent a very useful tool for the analysis of the low energy structure. Concerning the expansion in powers of m_s, however, the current situation leaves much to be desired. While some of the lattice results indicate, for instance, that the violations of the Okubo-Iizuka-Zweig rule in the quark condensate and in the decay constants are rather modest, others point in the opposite direction. I am confident that the dust will settle soon, so that the effective coupling constants that govern the dependence of the various quantities of physical interest on m_s can be determined, to next-to-next-to-leading order of the chiral expansion. The range of validity of ChPT can be extended by means of dispersive methods. The properties of the physical states occurring in the spectrum of QCD below KKbar threshold can reliably be investigated on this basis. In particular, as shown only rather recently, general principles of quantum field theory lead to an exact formula that expresses the mass and width of resonances in terms of observable quantities. The formula removes the ambiguities inherent in the analytic continuation from the real axis into the complex plane, which plagued previous determinations of the pole positions of broad resonances.
Talks given at QCD08 and Confinement8
References in corpus (10)
- A low-lying scalar meson nonet in a unitarized meson model
- The K^*_0(800) scalar resonance from Roy-Steiner representations of pi K scattering
- Precise Determination of the I=2 pipi Scattering Length from Mixed-Action Lattice QCD
- Integrating out strange quarks in ChPT
- Finding the sigma pole by analytic extrapolation of scattering data
- Matching Chiral Perturbation Theory and the Dispersive Representation of the Scalar Kpi Form Factor
- Model independent determination of the sigma pole
- Electromagnetic low-energy constants in ChPT
- On the two-loop contributions to the pion mass
- Precise analysis of pion-pion scattering data from Roy equations and forward dispersion relations