Hadron masses from a novel fermion action in lattice QCD

Full text: Due to the self-interacting nature of gluons, it is impossible to calculate analytically the nonperturbative properties of QCD, the theory of the strong interactions. The only way to perform such a calculation is via a numerical simulation on a discretised lattice with finite lattice spacing, a. Naive discretizations of the QCD action lead to O(a) errors and require extrapolations in a to the continuum limit to make contact with the real world. We use a novel fermion action which displays good scaling at finite lattice spacing, a, as well as having good chiral behaviour. For the first time we are able to efficiently perform simulations of hadron properties at quark masses approaching the chiral limit. We calculate hadron masses including excited states of the nucleon with negative parity and higher spin (jp = 1-/2 and 33/2). We find a N-Δ mass splitting in the quenched approximation 50% bigger than the physical value, rendering previous claims that the quenched approximation reproduces experimental values to within 10% invalid