We consider purely topological 2D Yang-Mills theory on a torus with the second Stiefel-Whitney class added to the Lagrangian in the form of a θ term. It will be shown that at θ = π there exists a class of S U ( 2 N ) / Z 2 ( N > 1 ) gauge theories with a twofold degenerate vacuum, which spontaneously breaks the time reversal and charge conjugation symmetries. The corresponding order parameter is given by the generator O of the Z N one-form symmetry.
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机译：我们考虑纯粹的拓扑2D阳磨机在一个圆环上的Torus论，其中第二个Stiefel-Whitney类以θ项的形式添加到拉格朗日。 将显示在θ=π处存在一类SU（2N）/ Z 2（N> 1）计具有双重退化真空的尺寸理论，其自发地破坏时间逆转和电荷共轭对称。 相应的订单参数由Z n单晶对称的发电机O给出。
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