= Mean-field itinerant ferromagnetic Goldstone mode
{title2=$E_{\mathbf q}\sim Dq^2$}
An isotropic spin-polarized metal has a degenerate magnetization direction and a long-wavelength transverse magnon with quadratic dispersion. Nonzero spin density pairs the two transverse broken generators into one <type-B Goldstone boson>. Exchange-split <Fermi surfaces> also support fermionic low-energy excitations; the magnon is distinct from longitudinal amplitude motion and the spin-flip continuum.
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