Lattice QCD at Finite Baryon Density With an Implementation of Dynamical Fermions

[摘要] Simulations of Lattice QCD at non-zero chemical potential (finite baryon density) have been performed with the inclusion of dynamical fermions. The fundamental difficulty in simulating QCD at finite density and investigating the colour deconfinement and chiral transitions quantitatively is that the Grassmann integration over the fermion fields is complex as a result of the introduction of the chemical potential in the Dirac matrix. The complex nature of the QCD finite density action prohibits the use of naive probabilistic methods in evaluating the functional integral. Early simulations which avoided the problem of the complex action by looking at the theory in the quenched approximation where the determinant is set to a constant value gave unphysical results. In the quenched theory the onset of chiral symmetry restoration which should be determined by the mass of the lightest particle with non-zero baryon number, did not occur at a chemical potential equal to one third of the proton mass (mu =mp/3) as expected, but appeared to occur at one half of the pion mass (mu =mpi/2) - a value which would extrapolate to zero in the chiral limit. The accepted explanation for the pathologies of the quenched theory is that the inclusion of the complex fermion determinant in the theory is essential. This thesis describes unquenched simulations of Lattice QCD at finite baryon density on 6.

[发布机构] University:University of Glasgow

[关键词] Theoretical physics, Quantum physics