Non-perturbative renormalization in coordinate space for Nf=2N_f=2 maximally twisted mass fermions with tree-level Symanzik improved gauge action

We present results of a lattice QCD application of a coordinate space renormalization scheme for the extraction of renormalization constants for flavour non-singlet bilinear quark operators. The method consists in the analysis of the small-distance behaviour of correlation functions in Euclidean space and has several theoretical and practical advantages, in particular: it is gauge invariant, easy to implement and has relatively low computational cost. The values of renormalization constants in the X-space scheme can be converted to the MSbar scheme via 4-loop continuum perturbative formulae. Our results for $N_f=2$ maximally twisted mass fermions with tree-level Symanzik improved gauge action are compared to the ones from the RI-MOM scheme and show full agreement with this method.Comment: 29 pages, 7 figures, 6 table

Short distance singularities and automatic O(aa) 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.Comment: 12 pages, corrected proof for topological susceptibility, version published in JHE

Lattice Hamiltonian approach to the Schwinger model: further results from the strong coupling expansion

We employ exact diagonalization with strong coupling expansion to the massless and massive Schwinger model. New results are presented for the ground state energy and scalar mass gap in the massless model, which improve the precision to nearly $10^{-9}$. We also investigate the chiral condensate and compare our calculations to previous results available in the literature. Oscillations of the chiral condensate which are present while increasing the expansion order are also studied and are shown to be directly linked to the presence of flux loops in the system.Comment: 7 pages, 6 figures, to appear in PoS(Lattice 2014)31

Topological susceptibility from twisted mass fermions using spectral projectors

We discuss the computation of the topological susceptibility using the method of spectral projectors and dynamical twisted mass fermions. We present our analysis concerning the O(a)-improvement of the topological susceptibility and we show numerical results for Nf=2 and Nf=2+1+1 flavours, performing a study of the quark mass dependence in terms of leading order chiral perturbation theory.Comment: 7 pages, 3 figures; presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German