We investigate the thermal QCD transition with two flavors of maximally twisted mass fermions for a set of pion masses, 300 MeV

A lot of effort in lattice simulations over the last years has been devoted to studies of the QCD deconfinement transition. Most state-of-the-art simulations use rooted staggered fermions, while Wilson fermions are affected by large systematic uncertainties, such as coarse lattices or heavy sea quarks. Here we report on an ongoing study of the transition, using two degenerate flavours of nonperturbatively O(a) improved Wilson fermions. We start with N t = 12 and 16 lattices and pion masses of 600 to 450 MeV, aiming at chiral and continuum limits with light quarks.

We present numerical results for the phase diagram of lattice QCD at finite temperature in the formulation with twisted mass Wilson fermions and a tree-level Symanzik-improved gauge action. Our simulations are performed on lattices with temporal extent N ¼ 8, and lattice coupling ranging from strong coupling to the scaling domain. Covering a wide range in the space spanned by the lattice coupling and the hopping and twisted mass parameters and , respectively, we obtain a comprehensive picture of the rich phase structure of the lattice theory. In particular, we verify the existence of an Aoki phase in the strong coupling region and the realization of the Sharpe-Singleton scenario at intermediate couplings. In the weak coupling region we identify the phase boundary for the physical finite temperature phase transition/crossover. Its shape in the three-dimensional parameter space is consistent with Creutz's conjecture of a cone-shaped thermal transition surface.

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We give an update on our current project to determine the transition temperature and the order of the deconfinement transition in the chiral limit of two flavour QCD. We use nonperturbatively O(a) improved Wilson fermions of the Sheikholeslami-Wohlert type, employing the efficient deflation accelerated DDHMC algorithm. We start at lattices with N t ≥ 12 and pion masses below 600 MeV, aiming at chiral and continuum limits with light quarks.