  Motivated by recent transport and neutron scattering experiments suggesting
an orientational symmetry breaking in underdoped cuprates we present a
theoretical study of Raman scattering near a d-wave Pomeranchuk instability
(PI). The d-wave component of Raman scattering from electrons and phonons
allows to study directly order parameter fluctuations associated with the PI.
Approaching the PI from the normal state by lowering the temperature a central
peak emerges both in electronic and, as an additional low-frequency feature, in
phononic scattering. Approaching the PI in the superconducting state at low
temperature by decreasing the doping concentration the central peak is replaced
by a soft mode with strongly decreasing width and energy and increasing
spectral weight. These predicted low-energy features in Raman scattering could
confirm in a rather direct way the presence of a PI in high-temperature cuprate
superconductors and in Sr3Ru2O7.
