Chiral repulsion in the pion-nucleus optical potential

It is shown that there exist additional sizeable sources of repulsion in the S-wave pion-nucleus optical potential of chiral origin. It is found that (${\mathit{b}}_0$ ${)}_{\mathrm{rchiral}}$≃-0.${011\mathrm{m}}_{\mathrm{\pi }}^{\mathrm{-}1}$ and (Re${\mathit{B}}_0$ ${)}_{\mathrm{chiral}}$≃-0.${023\mathrm{m}}_{\mathrm{\pi }}^{\mathrm{-}4}$ using cloudy bag form factors. Taking medium enhancement into account, this repulsion seems to be enough to offset both Galilean attraction (∝ρ) and the attraction in Re$B_0$(∝${\rho }^2$) from Δ-hole pairs.