QCD at θ ∼ π.
نویسنده
چکیده
Taking into account the terms ∼ m 2 in the effective chiral lagrangian , we show that, at θ = π, the theory with 2 light quarks of equal mass involves two degenerate vacuum states separated by a barrier. For N f = 3, the energy barrier between two vacua appears already in the leading order in mass. This corresponds to the first order phase transition at θ = π. The surface energy density of the domain wall separating two different vacua is calculated. In the immediate vicinity of the point θ = π, two minima of the potential still exist, but one of them becomes metastable. The probability of the false vacuum decay is estimated.
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