Resonance effects in pion and kaon decay constants

Understand

In this article we study impact of the lightest vector and scalar resonance multiplets in the pion and kaon decay constants up to next-to-leading order in the $1/N_C$ expansion, i.e., up to the one-loop level.

• The $F_\pi$ and $F_K$ predictions obtained within the framework of Resonance Chiral Theory are confronted with lattice simulation data.
• The vector loops (and the $\rho-\pi\pi$ coupling $G_V$ in particular) are found to play a crucial role in the determination of the Chiral Perturbation Theory couplings $L_4$ and $L_5$ at next-to-leading order in $1/N_C$.
• Puzzling, values of $G_V < 40$ MeV seem to be necessary to agree with current phenomenological results for $L_4$ and $L_5$.