Reducing cutoff effects in maximally twisted LQCD close to the chiral limit

When analyzed in terms of the Symanzik expansion, lattice correlators of multi-local (gauge-invariant) operators with non-trivial continuum limit exhibit in maximally twisted lattice QCD “infrared divergent” cutoff effects of the type a/(mπ) h, 2k ≥ h ≥ 1 (k, h integers), which tend to become numerically large when the pion mass gets small. We prove that, if the action is O(a) improved à la Symanzik or, alternatively, the critical mass counter-term is chosen in some “optimal” way, these lattice artifacts are reduced to terms that are at worst of the order a(a/mπ) k−1, k ≥ 1. This implies that the continuum extrapolation of lattice results is smooth at least down to values of the quark mass, mq, satisfying the order of magnitude inequality mq > a ΛQCD.