Chiral Shielding

TL;DR

This paper introduces a chiral soft pion theorem that explains why certain scalar mesons are difficult to detect in various processes, and shows how it constrains scalar meson transitions to be dominated by meson loops rather than quark loops.

Contribution

It presents a novel chiral soft pion theorem that shields scalar mesons from detection and constrains scalar meson transitions to meson loops, extending understanding of meson interactions.

Findings

Scalar mesons are shielded from detection by the chiral soft pion theorem.

Scalar meson transitions are governed by meson loops, not quark loops.

Application of the theorem to specific meson decays confirms its predictions.

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.