Surface tension of dense matter at the chiral phase transition

Abstract: If a first-order phase transition separates nuclear and quark matter at large baryon density, an interface between these two phases has a nonzero surface tension. We calculate this surface tension within a nucleon-meson model for domain walls and bubbles. Various methods and approximations are discussed and compared, including a numerical evaluation of the spatial profile of the interface. We also compute the surface tension at the other first-order phase transitions of the model: the nuclear liquid-gas transition and, in the parameter regime where it exists, the direct transition from the vacuum to the (approximately) chirally symmetric phase. Identifying the chirally symmetric phase with quark matter - our model does not contain explicit quark degrees of freedom - we find maximal surface tensions of the vacuum-quark transition $\Sigma_{\rm VQ}\sim 15 \, {\rm MeV}/{\rm fm}^2$, relevant for the surface of quark stars, and of the nuclear-quark transition $\Sigma_{\rm NQ}\sim 10 \, {\rm MeV}/{\rm fm}^2$, relevant for hybrid stars and for quark matter nucleation in supernovae and neutron star mergers.