 Skyrmion hedgehog ansatz

The unit Skyrmion has a spherically symmetric ansatz with Pauli matrices $\mathbf{\sigma }$, $f(0)=\pi$ and $f(\infty )=0$. The baryon number isThe radial profile is obtained from the Skyrme model variational equation. Spatial rotations and isospin rotations act on the same hedgehog orientation, leaving only three independent rotational collective coordinates.