  We study particle-hole instabilities in the framework of the spin-fermion
(SF) model. In contrast to previous studies, we assume that adjacent hot spots
can overlap due to a shallow dispersion of the electron spectrum in the
antinodal region. In addition, we take into account effects of a remnant low
energy and momentum Coulomb interaction. We demonstrate that at sufficiently
small values $|\varepsilon (\pi ,0)-E_{F}|\lesssim \Gamma $, where $E_{F}$ is
the Fermi energy, $\varepsilon \left( \pi ,0\right) $ is the energy in the
middle of the Brillouin zone edge, and $\Gamma $ is a characteristic energy of
the fermion-fermion interaction due to the antiferromagnetic fluctuations, the
leading particle-hole instability is a d-form factor Fermi surface deformation
(Pomeranchuk instability) rather than the charge modulation along the Brillouin
zone diagonals predicted within the standard SF model previously. At lower
temperatures, we find that the deformed Fermi surface is further unstable to
formation of a d-form factor charge density wave (CDW) with a wave vector along
the Cu-O-Cu bonds (axes of the Brillouin zone). We show that the remnant
Coulomb interaction enhances the d-form factor symmetry of the CDW. These
findings can explain the robustness of this order in the cuprates. The
approximations made in the paper are justified by a small parameter that allows
one an Eliashberg-like treatment. Comparison with experiments suggests that in
many cuprate compounds the prerequisites for the proposed scenario are indeed
fulfilled and the results obtained may explain important features of the charge
modulations observed recently.
