  Several instabilities competing with the d-wave singlet pairing were proposed
for high-Tc cuprates. One of them is the d-wave Fermi surface deformation
(dFSD), which is generated by forward scattering. In this paper, correlation
functions of the dFSD are calculated within the random phase approximation. In
the normal state, the excitation spectrum shows a low energy peak, which
smoothly connects to critical fluctuations of the dFSD at lower temperature.
The competition with the d-wave pairing, however, blocks the critical
fluctuations. The whole spectral weight is transferred to high energy and a
pronounced peak appears there in the d-wave pairing state. This peak is an
overdamped collective mode of the dFSD and can grow to be a resonance mode at
moderate finite wavevectors.
