  The medium modifications of antikaons in dense matter are studied in a
coupled channel calculation for scenarios more closely related to the
environment encountered in heavy-ion collisions. We find that the optical
potential of the antikaons turns repulsive or is drastically reduced for finite
momenta or finite temperature. Hence, the antikaon mass does not decrease
substantially in heavy-ion collisions to provide an explanation for the
observed antikaon production rates at threshold. We demonstrate that the
in-medium production cross section of antikaons via pions and Sigma hyperons is
remarkably enhanced up to an order of magnitude. The effect of in medium
correction on the resulting kaon spectra is studied within a transport model.
We find that both in medium correction lead to about the same enhancement of
the spectrum. However, once the temperature dependence is taken into account no
enhancement is found.
