Robustness of the Hedgehog Skyrmion

We investigate the radial profile function of the hedgehog Skyrmion with unit baryon number in generic EFTs (effective field theories) of pions. The analysis assumes chiral symmetry and ignores the pion mass term. The Skyrmion is always smooth, because it has no point source at the origin, and terms in the EFT with higher numbers of pion derivatives do not result in uncontrolled large corrections or singularities there. The profile varies in quite a limited way as the terms in the EFT change, and a universal profile function is proposed.