Spectrum of quenched twisted mass lattice QCD at maximal twist

Hadron masses are computed from quenched twisted mass lattice QCD for a degenerate doublet of up and down quarks with the twist angle set to pi/2, since this maximally twisted theory is expected to be free of linear discretization errors. Two separate definitions of the twist angle are used, and the hadron masses for these two cases are compared. The flavor breaking, that can arise due to twisting, is discussed in the context of mass splittings within the Delta(1232) multiplet.Comment: 23 pages, 16 figures, added discussion of pion decay constan

Strange quarks in quenched twisted mass lattice QCD

Two twisted doublets, one containing the up and down quarks and the other containing the strange quark with an SU(2)-flavor partner, are used for studies in the meson sector. The relevant chiral perturbation theory is presented, and quenched QCD simulations (where the partner of the strange quark is not active) are performed. Pseudoscalar meson masses and decay constants are computed; the vector and scalar mesons are also discussed. A comparison is made to the case of an untwisted strange quark, and some effects due to quenching, discretization, and the definition of maximal twist are explored.Comment: 37 pages, 12 figures, accepted for publicatio

Twisted mass QCD for the pion electromagnetic form factor

The pion form factor is computed using quenched twisted mass QCD and the GMRES-DR matrix inverter. The momentum averaging procedure of Frezzotti and Rossi is used to remove leading lattice spacing artifacts, and numerical results for the form factor show the expected improvement with respect to the standard Wilson action. Although some matrix inverters are known to fail when applied to twisted mass QCD, GMRES-DR is found to be a viable and powerful option. Results obtained for the pion form factor are consistent with the published results from other O(a) improved actions and are also consistent with the available experimental data.Comment: 19 pages, 12 figure

Parton Distribution Functions with Twisted Mass Fermions

We present a first Wilson twisted mass fermion calculation of the matrix element between pion states of the twist-2 operator, which is related to the the lowest moment of the valence quark parton distribution function in a pion. Using Wilson twisted mass fermions in the quenched approximation we demonstrate that can be computed at small pseudoscalar meson masses down to values of order 250 MeV. We investigate the scaling behaviour of this physically important quantity by applying two definitions of the critical mass and observe a scaling compatible with the expected O(a^2) behaviour in both cases. A combined continuum extrapolation allows to obtain reliable results for at very small pseudoscalar meson masses, which previously could not be explored by lattice QCD simulations.Comment: 15 pages, 3 figure