  In a two or three dimensional ferromagnetic XXZ model, a low energy
excitation mode above a magnetic domain wall is gapless, whereas all of the
usual spin wave excitations moving around the whole crystal are gapful.
Although this surprising fact was already proved in a mathematically rigorous
manner, the gapless excitations have not yet been detected experimentally. For
this issue, we show theoretically that the gapless excitations appear as the
dynamical fluctuations of the experimental observable, magnetoresistance, in a
ferromagnetic wire. We also discuss other methods (e.g., ferromagnetic
resonance and neutron scattering) to detect the gapless excitations
experimentally.
