$\gamma \gamma \to {\pi }^0{\pi }^0$ as a test for the existence of a light $\sigma$ meson

Abstract

We work out predictions of the Linear Sigma Model for the $\gamma \gamma \to {\pi }^0{\pi }^0$ cross section. We consider the sigma width, which is introduced in a consistent way with chiral Ward identities. The results of Chiral Perturbation Theory are recovered in the $m_{\sigma }\to \infty$ limit. A fit to existing experimental results is consistent with a light and broad $\sigma$ meson.

Comments: 7 pages, 3 figures. The sigma width is introduced in a consistent way with chiral symmetry. Results for the cross section are affected by the corresponding changes