Former APS President Thesis Defence

Former APS President Joaquin Grefa defended his thesis this spring. The APS Team Congratulates Joaquin on becoming a doctor.
Abstract: Strongly interacting matter undergoes a crossover phase transition at high temperatures and zero net-baryon density. A key question in Quantum Chromodynamics (QCD) is whether a dense quark-gluon system exhibits critical phenomena when breaking the balance between quarks and antiquarks. Lattice QCD studies suggest that a critical point can only emerge in the baryon-dense domain, which is challenging to describe through ab initio calculations. In this dissertation, I employ a bottom-up Einstein-Maxwell-dilaton (EMD) holographic model, which reproduces first principle lattice QCD thermodynamics at zero and small density and reflects the near-perfect fluidity of the quark-gluon plasma (QGP), to describe the hot and dense QGP at finite temperature and density. I significantly extend the baryon density coverage of the equation of state for hot and dense quark-gluon matter thanks to new numerical techniques to map holographic black hole solutions to the QCD phase diagram. This allows us to locate the predicted critical point and the first-order phase transition line over a wide region of the phase diagram. Comparisons with the most recent lattice results for the QCD thermodynamics are also presented. The EMD model is also employed to determine several transport coefficients of the hot and baryon-rich quark-gluon plasma at the crossover, the critical point and across the first-order phase transition line. These transport coefficients include the shear and bulk viscosities, baryon and ther- mal conductivities, baryon diffusion, jet quenching parameter qˆ, heavy-quark drag force, and Langevin diffusion coefficients. Finally, Bayesian inference methods are applied within the EMD model to forecast the QCD equa- tion of state throughout the phase diagram. We numerically derive the posterior probability distri- bution for holographic model parameters based on lattice data at zero chemical potential and extract their most probable values. Enhanced calculations allow us to sample a large number of data fits us- ing Monte Carlo techniques, providing an estimate for the critical point’s location and the associated statistical error bands. This research offers insights into the dense quark-gluon plasma, its transport coefficients, and the critical point location, which can be probed in heavy ion collision experiments.