Lattice measurement of αs with a realistic charm quark

We report on an estimate of αs, renormalised in the MS¯ scheme at the τ and Z0 mass scales, by means of lattice QCD. Our major improvement compared to previous lattice calculations is that, for the first time, no perturbative treatment at the charm threshold has been required since we have used statistical samples of gluon fields built by incorporating the vacuum polarisation effects of u/d, s and c sea quarks. Extracting αs in the Taylor scheme from the lattice measurement of the ghost-ghost-gluon vertex, we obtain αsMS¯(mZ2)=0.1200(14) and αsMS¯(mτ2)=0.339(13).