Status of chiral perturbation theory for light mesons

Abstract

The status of chiral perturbation theory in the meson sector is illustrated with several topical examples. The longtime discrepancy between theory and experiment for the charged pion polarizabilities has now been resolved in favour of the chiral SU(2) result to next-to-next-to-leading order. For chiral SU(3), the main obstacles are the large number of badly known coupling constants (LECs) and the lack of convergence of the low-energy expansion in many cases of interest. I describe a new global fit of the LECs in the strong sector that leads to a prediction of the CKM matrix element $V_{us}$ in agreement with the latest lattice determinations. The slow convergence of the chiral series is particularly acute in transitions with strong final-state interactions calling for dispersive treatments. The status of dispersive approaches is reviewed for $K_{\ell 4}$ decays and for $\eta ->3\pi$ decays where precise measurements of Dalitz plot distributions have recently become available.

18 pages, to appear in Proc. of 8th Int. Workshop on Chiral Dynamics, Pisa, Italy, 2015

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• The pion-pion scattering amplitude. IV: Improved analysis with once subtracted Roy-like equations up to 1100 MeV
• Mesonic low-energy constants
• Standard-model prediction for direct CP violation in $K\to \pi \pi$ decay
• $\eta \to 3\pi$ at Two Loops In Chiral Perturbation Theory
• Isospin breaking in Kl4 decays
• Three-body Final State Interaction in $\eta \to 3\pi$
• Integrating out strange quarks in ChPT
• Measurement of the charged-pion polarisability
• Measurement of the Matrix Elements for the Decays $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ and $\eta /{\eta }^{\prime }\to {\pi }^0{\pi }^0{\pi }^0$
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• The kaon semileptonic form factor in Nf=2+1 domain wall lattice QCD with physical light quark masses

Cited by in corpus (3)

• Chiral Lagrangian and chiral quark model from confinement in QCD
• Theoretical aspects of Chiral Dynamics
• Chiral dynamics with confinement versus the standard chiral theory