Light quarks with twisted mass fermions

We investigate Wilson twisted mass fermions in the quenched approximation using different definitions of the critical bare quark mass mc to realize maximal twist and, correspondingly, automatic O(a) improvement for physical observables. A particular definition of mc is given by extrapolating the value of mc obtained from the PCAC relation at non-vanishing bare twisted quark mass μ to μ=0. Employing this improved definition of the critical mass the Wilson twisted mass formulation provides the possibility to perform reliable simulations down to very small quark masses with correspondingly small pion masses of mπ≃250MeV, while keeping the cutoff effects of O(a2) under control.