In conventional matter, quarks and gluons are always confined in protons, neutrons and other hadrons. However, a transition to deconfined quark-gluon matter is supposed to take place under extreme conditions of temperature and density, comparable to those found in the early universe, in the core of neutron stars and in relativistic nucleus-nucleus collision experiments. At low net baryon density, lattice QCD simulations have found the transition to a quark-gluon plasma to be a smooth crossover. However, a first-order phase transition line, ending in a second-order critical point, is expected at sufficiently large baryon density. Due to the QCD sign problem, the high-density regime is currently inaccessible to first-principle numerical calculations, and the QCD critical point remains a conjecture. Here, we present results drawn from a phenomenological model based on the gauge-gravity duality. In our approach, dubbed black-hole
engineering, this model is tweaked so as to reproduce established results at low net baryon density, and applied to predict the equation of state of strongly-interacting matter in the high-density regime. We perform a Bayesian analysis of this model, having as inputs lattice QCD results for the low-density equation of state, and discuss the implications of our results for the QCD phase diagram.
