Dynamical Twisted Mass Fermions with Light Quarks

We present the results of an extended scaling test of quenched Wilson twisted mass QCD. We fix the twist angle by using two definitions of the critical mass, the first obtained by requiring the vanishing of the pseudoscalar meson mass m_PS for standard Wilson fermions and the second by requiring restoration of parity at non-zero value of the twisted mass mu and subsequently extrapolating to mu=0. Depending on the choice of the critical mass we simulate at values of beta in [5...

As a test of quenched lattice twisted mass QCD, we compute the non-perturbatively O($a$) improved pseudoscalar and vector meson masses and the pseudoscalar decay constant down to $M_{\rm PS}/M_{\rm V} = 0.467(13)$ at $\beta=6$ in large volume. We check the absence of exceptional configurations and -- by further data at $\beta=6.2$ -- the size of scaling violations. The CPU time cost for reaching a given accuracy is close to that with ordinary Wilson quarks at $M_{\rm PS}/M_{\...

In this contribution, results from $N_f=2$ lattice QCD simulations at one lattice spacing using twisted mass fermions with a clover term at the physical pion mass are presented. The mass splitting between charged and neutral pions (including the disconnected contribution) is shown to be around $20(20)~\mathrm{MeV}$. Further, a first measurement using the clover twisted mass action of the average momentum fraction of the pion is given. Finally, an analysis of pseudoscalar meso...

We summarize four contributions about dynamical twisted mass fermions. The resulting report covers results for N_f=2 obtained from three different gauge actions, namely the standard Wilson plaquette gauge action, the DBW2 and the tree-level Symanzik improved gauge action. In addition, first results for N_f=2+1+1 flavours of twisted mass fermions are discussed.

We present a lattice QCD determination of the $b$-quark mass and of the $f_{B_s}$ and $f_B$ decay constants performed with $N_f = 2 + 1 + 1$ twisted mass Wilson fermions. We have used simulations at three values of the lattice spacing generated by ETMC with pion masses ranging from 210 to 440 MeV. To obtain physical quantities we performed a combined chiral and continuum limit and an extrapolation in the heavy quark mass from the charm to the $b$-quark region using suitable r...

We compare the behavior of overlap fermions, which are chirally invariant, and of Wilson twisted mass fermions at full twist in the approach to the chiral limit. Our quenched simulations reveal that with both formulations of lattice fermions pion masses of O(250 MeV) can be reached in practical applications. Our comparison is done at a fixed value of the lattice spacing a=0.123 fm. A number of quantities are measured such as hadron masses, pseudoscalar decay constants and qua...

The masses of the low lying baryons are evaluated using a total of ten ensembles of dynamical twisted mass fermion gauge configurations. The simulations are performed using two degenerate flavors of light quarks, and a strange and a charm quark fixed to approximately their physical values. The light sea quarks correspond to pseudo scalar masses in the range of about 210~MeV to 430~MeV. We use the Iwasaki improved gluonic action at three values of the coupling constant corresp...

We present results for the light quark masses in lattice QCD with two degenerate flavours of dynamical fermions. We used configurations generated by the UKQCD and QCDSF collaborations at six different combinations of beta and kappa_sea.

We report on the scaling of basic hadronic observables in lattice QCD with N_f=2 maximally twisted Wilson dynamical quarks. We give preliminary results for some of the Gasser-Leutwyler low energy constants, the chiral condensate and the average mass of u and d quarks.

Wilson's formulation of lattice QCD is attractive for many reasons, but perhaps mainly because of its simplicity and conceptual clarity. Numerical simulations of the Wilson theory (and of its improved versions) tend to be extremely demanding, however, to the extent that they rapidly become impractical at small quark masses. Recent advances in simulation algorithms now allow such simulations to be pushed to significantly smaller masses without having to compromise in other way...