  We consider two classes of helical magnets. The first one has magnetic
ordering close to antiferromagnet and the second one has magnetic ordering
close to ferromagnet. The first case is relevant to cuprate superconductors and
the second case is realized in FeSrO$_3$ and FeCaO$_3$. We derive the effective
field theories for these cases and calculate corresponding excitation spectra.
We demonstrate that the "hourglass" spin-wave dispersion observed
experimentally in cuprates is a fingerprint of the "antiferromagnetic spin
spiral state". We also show that quantum fluctuations are important for the
"ferromagnetic spin spiral", they influence qualitative features of the
spin-wave dispersion.

Strongly Correlated Electrons