  We study theoretically the electromagnon and its optical spectrum (OS) of the
terahertz-frequency regime in the magnetic-spiral-induced multiferroic phases
of the rare-earth (R) Mn perovskites, RMnO3, taking into account the elliptical
deformation or the higher harmonics of the spiral spin configuration, which has
been missed so far. A realistic spin Hamiltonian, which gives phase diagrams in
agreement with experiments, resolves a long standing puzzle, i.e., the
double-peak structure of the OS with a larger low-energy peak originating from
magnon modes hybridized with the zone-edge state. We also predict the magnon
branches associated with the electromagnon, which can be tested by
neutron-scattering experiment.
