The $N_c$-dependence of the vertices $PPP\gamma$, where $P$ is a pseudoscalar meson and $N_c$ is the number of colors, is analyzed with regard for the $N_c$-dependence of the quark charges. It is shown that the best processes for the determination of $N_c$ are the reactions $K\gamma \to K\pi$ and $\pi^pm\gamma\to\pi^\pm\eta$ as well as the decay $\eta\ra\pi^+\pi^-\gamma$. The measurement of the cross section $\sigma(\pi^-\gamma\ra\pi^-\eta)$ at the VES facility at the IHEP agrees with the value $N_c=3$.
Categories: hep-ph