Compton scattering and pion number in nuclei

Abstract

We explore the relation between the spin-independent Compton amplitude and the pion excess number per nucleon n π in nuclear matter and for the dueteron. We show that the enhancement factor K of the photonuclear sum rule, which appears as a meson exchange correction to this amplitude, is related to n π by K ≈ 16 3 n πM〈ω π −1〉 where 〈ω π −1〉 is the mean inverse pion energy. This relation is justified by the consideration of the chiral limit where the pion mass vanishes.