We calculate the critical exponents of the threshold singularity for the spectral density of the XXZ-spin chain at zero magnetic field for the lower threshold. We show that the corresponding phase shifts are momentum independent and coincide with predictions of the effective mobile impurity Hamiltonian approach.

中文翻译：

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XXZ 自旋链中的阈值奇点

我们计算了下阈值在零磁场下 XXZ 自旋链的光谱密度的阈值奇异性的临界指数。我们表明，相应的相移与动量无关，并且与有效移动杂质哈密顿方法的预测一致。