Reducing cutoff effects in maximally twisted lattice QCD close to the chiral limit

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  • 23 March 2005
Abstract
When analyzed in terms of the Symanzik expansion, the expectation values 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^{2k}/(m_\pi^2)^{h}, 2k>=h>=1, which become numerically dangerous when the pion mass gets small. We prove that, if the critical mass counter-term is chosen in some ``optimal'' way or, alternatively, the action is O(a) improved a`la Symanzik, the leading cutoff effects of this kind (i.e. those with h=2k) can all be eliminated. Once this is done, the remaining next-to-leading ``infrared divergent'' effects are only of the kind a^{2}(a^2/m_\pi^2)^{k}, k>=1. This implies that the continuum extrapolation of lattice results is smooth at least down to values of the quark mass, m_q, satisfying the order of magnitude inequality m_q>a^2\Lambda^3_{QCD}.

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