= Toroidal two-Skyrmion
{title2=$B=2$}
The standard low-energy $B=2$ <Skyrmion> in the ordinary <Skyrme model> has a toroidal baryon-density shape, with axial density symmetry $D_{\infty h}$. Its proper combined field symmetries have an $O(2)$-type stabilizer. The angular ansatz $R(z)=z^2$ in the <rational map approximation for Skyrmions> explains the axial relation $R(e^{i\theta}z)=e^{2i\theta}R(z)$: spatial rotation through $\theta$ is accompanied by <isorotation> through $2\theta$. The angular density vanishes at the two axial directions, yielding the toroidal hole. This describes the familiar minimal branch and a useful approximate field; it is not an assertion that every degree-two field is toroidal.
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