Properties of pseudoscalar flavour-singlet mesons from 2+1+1 twisted   mass lattice QCD
  We study properties of pseudoscalar flavour-singlet mesons from Wilson twisted mass lattice QCD with Nf=2+1+1 dynamical quark flavors. Results for masses are presented at three values of the lattice spacing and light quark masses corresponding to values of the pion mass from 230 MeV to 500 MeV. We briefly discuss scaling effects and the light and strange quark mass dependence of the eta mass. In addition we present an exploratory study using Osterwalder-Seiler type strange and charm valence quarks. This approach avoids some of the complications of the twisted mass heavy doublet. We present first results for matching valence and unitary actions and a comparison of statistical uncertainties. 
Krzysztof Cichy, Vincent Drach, Elena Garcia-Ramos, Karl Jansen, Chris   Michael, Konstantin Ottnad, Carsten Urbach, Falk Zi...
hep-lat hep-ph