Frequency correlations of QPOs based on a disk oscillation model in warped disks

In previous papers, we proposed a model that high-frequency quasi-periodic oscillations (QPOs) observed in black-hole and neutron-star X-ray binaries are disk oscillations (inertial-acoustic and/or g-mode oscillations) resonantly excited on warped disks. In this paper we examine whether time variations of the QPOs and their frequency correlations observed in neutron-star X-ray binaries can be accounted for by this disk-oscillation model. By assuming that a warp has a time-dependent precession, we can well describe the observed frequency correlations among kHz QPOs and low-frequency QPOs over a wide range of frequencies.