Short distance singularities and automatic O($a$) improvement: the cases   of the chiral condensate and the topological susceptibility
  Short-distance singularities in lattice correlators can modify their Symanzik expansion by leading to additional O($a$) lattice artifacts. At the example of the chiral condensate and the topological susceptibility, we show how to account for these lattice artifacts for Wilson twisted mass fermions and show that the property of automatic O($a$) improvement is preserved at maximal twist. 
Krzysztof Cichy, Elena Garcia-Ramos, Karl Jansen
hep-lat