The QCD Equation of State at High Temperatureand Small Density from the LatticeChuan MiaoFalkult at fur PhysikUniversit at BielefeldThesis submitted for the Degree of Doctor of Philosophy in theUniversit at Bielefeld March 2008Contents1 Introduction 11.1 A short introduction to the lattice QCD . . . . . . . . . . . . . . . . . . . . 51.1.1 Gauge action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.1.2 Naive fermion action . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.1.3 Gauge eld theory and QCD on lattice . . . . . . . . . . . . . . . . . 101.2 Lattice QCD at nite temperature and density . . . . . . . . . . . . . . . . 111.3 Decon nement and chiral transition . . . . . . . . . . . . . . . . . . . . . . 141.3.1 Decon nement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.3.2 Chiral transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181.4 Improved actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201.4.1 Improved gauge action . . . . . . . . . . . . . . . . . . . . . . . . . . 211.4.2 Improved staggered fermion action . . . . . . . . . . . . . . . . . . . 221.5 Monte Carlo simulation and RHMC algorithm . . . . . . . . . . . . . . . . 241.5.1 Monte Carlo simulations and Metropolis test . . . . . . . . . . . . . 241.5.2 Hybrid Monte Carlo . . . . . . . . . . . . . . . . . . . . . . . . . . . 251.5.3 Pseudo fermion and RHMC for QCD . . . . . . . . . . . . . . . . .