Low-Energy Constants from Resonance Chiral Theory

Understand

I discuss the recent attempts to build an effective chiral Lagrangian incorporating massive resonance states.

• A useful approximation scheme to organize the resonance Lagrangian is provided by the large-Nc limit of QCD.
• Integrating out the resonance fields, one recovers the usual chiral perturbation theory Lagrangian with explicit values for the low-energy constants, parameterized in terms of resonance masses and couplings.
• The resonance chiral theory generates Green functions that interpolate between QCD and chiral perturbation theory.