  We study the influence of spin-orbit interactions on quasiparticle
dispersions in two-dimensional electron and heavy-hole liquids in III-V
semiconductors. To obtain closed-form analytical results, we restrict ourselves
to spin-orbit interactions with isotropic spectrum and work within the screened
Hartree-Fock approximation, valid in the high-density limit. For electrons
having a linear-in-momentum Rashba (or, equivalently, Dresselhaus) spin-orbit
interaction, we show that the screened Hartree-Fock approximation recovers
known results based on the random-phase approximation and we extend those
results to higher order in the spin-orbit coupling. While the well-studied case
of electrons leads only to a weak modification of quasiparticle properties in
the presence of the linear-in-momentum spin-orbit interaction, we find two
important distinctions for hole systems (with a leading nonlinear-in-momentum
spin-orbit interaction). First, the group velocities associated with the two
hole-spin branches acquire a significant difference in the presence of
spin-orbit interactions, allowing for the creation of spin-polarized
wavepackets in zero magnetic field. Second, we find that the interplay of
Coulomb and spin-orbit interactions is significantly more important for holes
than for electrons and can be probed through the quasiparticle group
velocities. These effects should be directly observable in magnetotransport,
Raman scattering, and femtosecond-resolved Faraday rotation measurements. Our
results are in agreement with a general argument on the velocities, which we
formulate for an arbitrary choice of the spin-orbit coupling.
