  On a disk deformed to a non-axisymmetric form, a set of oscillations can be
excited by their resonant interaction through the disk deformation (Kato et al.
2011). This resonant instability process has been proposed to suggest a
possible cause of the high-frequency quasi-periodic oscillations (HF QPOs)
observed in black-hole low-mass X-ray binaries. In the present paper, we
examine whether the above-mentioned wave-wave resonant process can describe the
tidal instability and superhump in dwarf novae. The results show that the
process seems to well describe the observations. If this process is really the
cause of the tidal instability and superhump, a two-armed oscillation with high
frequency roughly on the magnitude of three times the orbital frequency is
present on disks, although its expected amplitude may be small.
