Chiral Extension of Lattice Field Theory with Ginsparg-wilson Fermions: Xqcd Actions, Small Imaginary Part of the Xqcd Fermion Determinant, ... and the Standard 5-d Domain-wall Action

Treating chiral symmetry in standard lattice QCD(quantum chromodynamics) approach has been a difficult issue. Due this difficulty, researchers often did extrapolations from un-physically massive u and d quarks. As a way for a better treatment of chiral symmetry, Brower, Shen and Tan proposed "chirally extended QCD" (also called XQCD) in 1994. An important basic scheme in XQCD is to add "irrelevant" terms to the action so that we have chiral symmetry on the lattice while having desired continuum limit. This book introduces part of the recent research of XQCD by R. Brower, C-I Tan, R. Edwards, F. Berruto, H. Neff, and K-T Lim that incorporates Ginsparg-Wilson fermions. It briefly explains the construction of continuum and lattice XQCD actions, introduces a numerical study of the imaginary part of the determinant of the coset XQCD Dirac operator, and shows step-by-step that the 4-d Yukawa Overlap XQCD fermion action can be derived from the standard 5-d domain-wall action. It would be useful to physicists and physics students specializing in QCD.