Multi-channel coupling of decay instability in three-dimensional low-beta plasma

Three-dimensional hybrid simulations have been carried out to verify the hypothesis of simultaneous multichannel decay of a large-amplitude Alfvén wave in a lowbeta plasma, e.g., in the shock-upstream region or the solar corona. Obliquely propagating daughter modes are excited along the perpendicular direction to the mean magnetic field at the same parallel wavenumbers and frequencies as the daughter modes driven by the field-aligned decay. We find that the transversal spectrum of waves is controlled by the multi-channel coupling of the decay process in low-beta plasmas and originates in the dispersion state of the shear Alfvén wave.