Prof. dr hab. David Blaschke

### Proving the existence of the QCD critical point by compact star observations

In order to prove the existence of a critical end point (CEP) in the QCD phase diagram it is sufficient to demonstrate that at zero temperature $T=0$ a first order phase transition exists as a function of the baryochemical potential $\mu$, since it is established knowledge from ab-initio lattice QCD simulations that at $\mu=0$ the transition on the temperature axis is a crossover. We present the argument that the observation of a gap in the mass-radius relationship for compact stars which proves the existence of a so-called third family (aka "mass twins") will imply that the $T=0$ equation of state of compact star matter exhibits a strong first order transition with a latent heat that s satisfies $\Delta\epsilon/\epsilon_c >0.6$ [Alford et al., arxiv:1302.4732]. Since such a strong first order transition under compact starconditions will remain first order when going to symmetric matter, this completes the argument that the observation of a disconnected branch (third family) of compact stars in the mass-radius diagram proves the existence of a CEP in QCD.