Chiral Shielding

Abstract

We demonstrate how a chiral soft pion theorem (SPT) shields the scalar meson ground state isoscalar $\sigma(600-700)$ and isospinor $\kappa(800-900)$ from detection in $a_{1}\to\pi(\pi\pi)_{\mathrm{swave}}$, $\gamma\gamma\to2\pi^{\circ}$, $\pi^{-}p\to\pi^{-}\pi^{+}n$ and $K^{-}p\to K^{-}\pi^{+}n$ processes. While pseudoscalar meson PVV transitions are known to be determined by (only) quark loop diagrams, the above SPT also constrains scalar meson SVV transitions to be governed (only) by meson loop diagrams. We apply this latter SVV theorem to $a_{0}\to\gamma\gamma$ and $f_{0}\to\gamma\gamma$ decays.