  An expanding polariton condensate is investigated under pulsed nonresonant
excitation with a small laser pump spot. Far above the condensation threshold
we observe a pronounced increase in the dispersion curvature with a subsequent
linearization of the spectrum and strong luminescence from a ghost branch
orthogonally polarized with respect to the linearly polarized condensate
emission. The presence of the ghost branch has been confirmed in time-resolved
measurements. The dissipative and nonequilibrium effects in the
photoluminescence of polariton condensates and their excitations are discussed.
