Strong coupling methods for lattice QCD

Unger W. Strong coupling methods for lattice QCD. Bielefeld: Universität Bielefeld; 2021.Lattice QCD at finite baryon density suffers from the numerical finite density sign problem. Strong coupling methods, expanding in the inverse gauge coupling, give rise to alternative representations of the partition function that can make the sign problem milder. This Habilitation discusses the strong coupling methods developed by the author and colleagues to study lattice QCD at vanishing and non-vanishing baryon density. The main results summarized and covered in the attached papers are (1) chiral symmetry breaking and its restoration at zero temperature for a large number of flavors, (2) the QCD phase diagram, in particular the location of the chiral/nuclear critical endpoint, (3) bulk thermodynamics and (4) Hamiltonian formulation and Quantum Monte Carlo simulations. Most of the results were obtained via a dual formulation for lattice QCD derived from a strong coupling expansion. All results are limited to the strong coupling regime, i.e. valid on coarse lattices, where the sign problem is under control