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Register a new userA numerical reinvestigation of the Aoki phase with N_f=2 Wilson fermions at zero temperature
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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 $hbar{psi} i gamma_{5} tau^{3}psi$ was added to the fermion action. The order parameter $<bar{psi} i gamma_{5}tau^{3}psi>$ was computed with the Hybrid Monte Carlo algorithm at several values of $(beta,kappa,h)$ 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 $beta=4.0$ and 4.3, while we do not find parity-flavor breaking at $beta=4.6$ and 5.0.
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In this letter we report on a numerical investigation of the Aoki phase in the case of finite temperature which continues our former study at zero temperature. We have performed simulations with Wilson fermions at $beta=4.6$ using lattices with temporal extension $N_{tau}=4$. In contrast to the zero temperature case, the existence of an Aoki phase can be confirmed for a small range in $kappa$ at $beta=4.6$, however, shifted slightly to lower $kappa$. Despite fine-tuning $kappa$ we could not separate the thermal transition line from the Aoki phase.
We report on a numerical reinvestigation of the Aoki phase in full lattice QCD with two flavors of unimproved Wilson fermions. For zero temperature the Aoki phase can be confirmed at inverse coupling $beta=4.0$ and $beta=4.3$, but not at $beta=4.6$ and $beta=5.0$. At non-zero temperature the Aoki phase was found to exist also at $beta=4.6$.
The order of the thermal phase transition in the chiral limit of Quantum Chromodynamics (QCD) with two dynamical flavors of quarks is a long-standing issue and still not known in the continuum limit. Whether the transition is first or second order has important implications for the QCD phase diagram and the existence of a critical endpoint at finite densities. We follow a recently proposed approach to explicitly determine the region of first order chiral transitions at imaginary chemical potential, where it is large enough to be simulated, and extrapolate it to zero chemical potential with known critical exponents. Using unimproved Wilson fermions on coarse $N_t=4$ lattices, the first order region turns out to be so large that no extrapolation is necessary. The critical pion mass $m_pi^capprox 560$ MeV is by nearly a factor 10 larger than the corresponding one using staggered fermions. Our results are in line with investigations of three-flavour QCD using improved Wilson fermions and indicate that the systematic error on the two-flavour chiral transition is still of order 100%.
We present new data on the mass of the light and strange quarks from SESAM/T$chi$L. The results were obtained on lattice-volumes of $16^3times 32$ and $24^3times 40$ points, with the possibility to investigate finite-size effects. Since the SESAM/T$chi$L ensembles at $beta=5.6$ have been complemented by configurations with $beta=5.5$, moreover, we are now able to attempt the continuum extrapolation (CE) of the quark masses with standard Wilson fermions.
JLQCD collaboration recently started the $N_f=3$ QCD simulations with the $O(a)$-improved Wilson fermion action employing an exact fermion algorithm developed for odd number of quark flavors. It is found that this theory has an unexpected non-trivial phase structure in the $(beta,kappa)$ plane even at zero temperature. A detailed study is made to understand the nature of the observed phase transitions and to find the way of avoiding untolerably large lattice artifacts associated with the phase transition.
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