Orateur
Description
Neutron stars provide a unique laboratory for dense QCD, but extracting information about their microscopic composition requires both robust constraints on the equation of state (EOS) and accurate simulations of their dynamics. I will discuss recent progress along these complementary directions. First, I will show how model-agnostic EOS inference, constrained by chiral effective field theory, perturbative QCD, and multimessenger observations, strongly disfavors twin-star solutions. The few surviving cases require highly fine-tuned behavior: either a phase transition near saturation density or a rapid high-density crossover with a double-peaked speed of sound. Since neither exhibits conformalization on the second branch, the interpretation of twin stars as a robust signature of deconfinement is effectively ruled out. I will then present GRACE, a new open-source, GPU-accelerated framework for numerical relativity that evolves general-relativistic magnetohydrodynamics coupled to the Einstein equations in the Z4c formulation. I will discuss its validation, performance, and first binary neutron-star simulations, and outline how scalable numerical-relativity calculations can connect increasingly stringent dense-matter constraints to gravitational-wave observables from neutron-star mergers.