Abstract
In this paper, we discuss the vacuum structure of QCD with two flavors of Wilson fermions, inside the Aoki phase. We provide numerical evidence, coming from HMC simulations in 44, 64 and 84 lattices, supporting a vacuum structure for this model at strong coupling more complex than the one assumed in the standard wisdom, with new vacua where the expectation value of iψ¯γ5ψ can take non-zero values, and which can not be connected with the Aoki vacua by parity–flavor symmetry transformations.
Highlights
Two and three colors QCD with unimproved Wilson fermions started to be simulated in the early 80s [1,2]
In the other one there is no spontaneous symmetry breaking. This standard picture for the Aoki phase was questioned three years ago by three of us in [21], where we conjectured on the appearance of new vacua in the Aoki phase, which can be characterized by a non-vanishing vacuum expectation value of the flavor singlet pseudoscalar condensate iψγ5ψ, and which can not be connected with the Aoki vacua by parity–flavor symmetry transformations
If on the contrary the spectral density ρU (λ, κ) of the Hermitian Dirac–Wilson operator in a fixed background gauge field U is symmetric in λ, we argued in [21] on the appearance of other phases, which can be characterized by a non-vanishing vacuum expectation value of iψuγ5ψu + iψd γ5ψd, and which can not be connected with the Aoki vacua by parity–flavor symmetry transformations
Summary
Two and three colors QCD with unimproved Wilson fermions started to be simulated in the early 80s [1,2]. In the other one (the “first-order” scenario) there is no spontaneous symmetry breaking This standard picture for the Aoki phase was questioned three years ago by three of us in [21], where we conjectured on the appearance of new vacua in the Aoki phase, which can be characterized by a non-vanishing vacuum expectation value of the flavor singlet pseudoscalar condensate iψγ5ψ , and which can not be connected with the Aoki vacua by parity–flavor symmetry transformations.
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