Parametrizing the equation of state of cold and dense nuclear matter

Various functional parametrizations of the equation of state of cold nuclear matter are considered with regard to both their degree of stiffness and their causal behavior at high density. We show that (i) the inferred nuclear compressibility $K$ is strongly parametrization dependent when the measured pion multiplicity in central heavy ion collisions is fitted, and (ii) most of the commonly used equations of state are acausal at high density.