Recent results on light hadron and quark masses

Abstract

Recent results for the spectrum of light hadrons provide clear evidence for the failure of quenched QCD and encouraging signs that simulations with dynamical sea quarks rectify some of the discrepancies, although string breaking has not yet been observed. The use of perturbation theory to match lattice quark masses to continuum schemes remains questionable, but non-perturbative methods are poised to remove this uncertainty. The inclusion of dynamical sea quarks substantially reduces estimates of the light quark masses. New results for the lightest glueball and the lightest exotic hybrid state provide useful input to phenomenology, but still have limited or no treatment of mixing. The $O(a)$-improved Wilson quark action is well-established in quenched QCD for $β\geq 5.7$, with most parameters obtainable non-perturbatively, in which range scaling violations are small. Progress has also been made with high-order improvement schemes for both Wilson and staggered quarks.