Dynamical Twisted Mass Fermions with Light Quarks

We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf=2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non-perturbative RI-MOM renormalization procedur...

I review the main theoretical properties and some recent analytical and numerical investigations of the formulations of lattice QCD with chirally twisted Wilson quarks (also known as twisted mass lattice QCD).

We investigate Wilson twisted mass fermions in the quenched approximation using different definitions of the critical bare quark mass m_c to realize maximal twist and, correspondingly, automatic O(a) improvement for physical observables. A particular definition of m_c is given by extrapolating the value of m_c obtained from the PCAC relation at non-vanishing bare twisted quark mass mu to mu=0. Employing this improved definition of the critical mass the Wilson twisted mass for...

We present new results for light quark masses. The calculations are performed using two flavours of $O(a)$ improved Wilson fermions. We have reached lattice spacings as small as $a \sim 0.07$fm and pion masses down to $m_{\pi} \sim 340$MeV in our simulations. This gives us significantly better control on the chiral and continuum extrapolations.

Lattice formulations of QCD with Wilson fermions and a chirally twisted quark mass matrix provide an attractive framework for non-perturbative numerical studies. Owing to reparameterization invariance, the limiting continuum theory is just QCD. No spurious quark zero modes, which are responsible for the problem with exceptional configurations, can occur at finite values of the quark mass. Moreover, the details of the lattice formulation can be adjusted so as to simplify the r...

We present results for spectroscopy, quark masses and decay constants obtained from SESAM's and TkL's large statistics simulations of QCD with two dynamical Wilson fermions.

We compute the low lying eigenvalues of the Hermitian Dirac operator in lattice QCD with $N_{\rm f} = 2+1+1$ twisted mass fermions. We discuss whether these eigenvalues are in the $\epsilon$-regime or the $p$-regime of Wilson chiral perturbation theory ($\chi$PT) for twisted mass fermions. Reaching the deep $\epsilon$-regime is practically unfeasible with presently typical simulation parameters, but still the few lowest eigenvalues of the employed ensemble evince some charact...

In this proceeding contribution we report on the ongoing effort to understand and simulate Wilson twisted mass fermions in the so called epsilon regime.

We present a preliminary study of a chiral-gauge-invariant Wilson term for the Standard Model on a lattice. In the strong coupling limit for doublers, this Wilson term shows that the doublers of leptons (quarks) are anti-baryons (anti-leptoquarks), and they are decoupled by getting gauge invariant masses. We discuss that the possibility of achieving the low-energy Standard Model could be realized by the ``three-fermion-cuts'' at the weak coupling limit for normal modes, where...

I review recent theoretical developments and numerical results of twisted mass QCD. I argue that, combined with an efficient algorithm, twisted mass QCD can be an attractive QCD lattice action, to perform large scale simulations at small pion masses, where a matching with chiral perturbation theory can be performed. Open issues like flavour breaking effects are also addressed.