Numerical reinvestigation of the Aoki phase withNf=2Wilson fermions at zero temperature

Abstract

We report on a numerical reinvestigation of the Aoki phase in lattice QCD with two flavors of Wilson fermions where the parity-flavor symmetry is spontaneously broken. For this purpose an explicitly symmetry-breaking source term hψiγ5τ 3 ψ was added to the fermion action. The order parameter ψ iγ5τ 3 ψ was computed with the hybrid Monte Carlo algorithm at several values of (β, κ, h) on lattices of sizes 4 4 to 12 4 and extrapolated to h = 0. The existence of a parity-flavor breaking phase can be confirmed at β = 4.0 and 4.3, while we do not find parity-flavor breaking at β = 4.6 and 5.0.

Twisted mass QCD at finite temperature

“…This can be seen on the right hand side of Figure 3 where the real part of the Polyakov loop and its susceptibility are shown as functions of κ. Therefore, if an Aoki phase were found somewhere between κ = 0.16 and 0.20, this would be in contrast to the experience gained in previous investigations (with Wilson gauge action) [6] in which no clear separation of the Aoki phase from the thermal transition has been observed. As expected for the phase diagram at µ = 0, the κ value at which the Polyakov loop rises significantly shifts to lower values when β is increased.…”

“…The expected Aoki phase for small values of β (cf. [6]) is in the µ = 0 plane, since µ = 0 explicitly breaks the associated parity-flavour symmetry. For larger values of β , a conical surface is believed to mark the thermal transition between the hadronic and quark gluon regimes.…”

Determination of low-energy constants of Wilson chiral perturbation theory

“…Depending on the sign of a particular combination of Wilson LECs -commonly denoted as c 2 ∝ −(2W 6 + W 8 ) -either the Aoki-scenario [11] or a first order, so called Sharpe-Singleton [10] scenario is realised. Numerical evidence for both scenarios has been observed in lattice QCD simulations and dedicated studies of the associated phase diagrams have been performed by several groups [13][14][15][16][17][18][19][20][21][22][23][24].…”

Dynamical twisted mass fermions with light quarks

“…[49,50] at large gauge couplings corresponding to values of the lattice spacing a ≥ 0.2 fm. In other studies [51,52,53] signals of first order phase transitions were found for Wilson fermions with and without the clover term, see also Ref.…”