Free energy of bubbles and droplets in the quark-hadron phase transition

Using the MIT bag model, we calculate the free energy of droplets of quark-gluon plasma in a bulk hadronic medium, and of hadronic bubbles in a bulk quark-gluon plasma, under the assumption of vanishing chemical potentials. We investigate the validity of the multiple reflection expansion approximation, and we advise a novel procedure for calculating finite-size corrections to the free energy of hadronic bubbles in a bulk quark-gluon plasma. While our results agree largely with earlier calculations, we show that the usual multiple reflection expansion should be used with caution, and we propose a modification of the multiple reflection expansion, which makes this approximation agree nicely with direct numerical calculations. The results should be of relevance in connection with the cosmological quark-hadron transition as well as for ultrarelativistic heavy ion collisions.