发表机构
Institute of Theoretical Physics, Wrocław University of Science and Technology（弗罗茨瓦夫科技大学理论物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文利用扩展广义Kadanoff--Baym近似揭示其谱性质，发现该近似在强相互作用下谱函数出现负值，存在重要局限性。
AI 中文摘要
具有平均场传播子的广义Kadanoff--Baym近似越来越多地被用于模拟非平衡量子费米子和玻色子系统。与完整的Kadanoff--Baym方程相比，其平均场传播子大幅降低了计算成本，使得模拟的计算开销随传播时间线性增长。然而，广义Kadanoff--Baym近似的时间对角结构掩盖了输运方程碰撞积分内的谱性质。本文利用扩展的广义Kadanoff--Baym近似恢复并研究了这些隐藏的谱性质。对于Hubbard团簇，我们将通过扩展广义Kadanoff--Baym近似获得的基态谱函数与标准Kadanoff--Baym方程的结果进行了比较。在中等相互作用强度下，谱函数表现出良好的一致性。然而，在强相互作用下，出现了显著偏差，且通过扩展广义Kadanoff--Baym近似获得的谱函数变为负值。这些结果表明，尽管广义Kadanoff--Baym近似具有计算优势，但在强相互作用区域存在重要局限性，当相互作用足够强时可能产生非物理的谱性质。
英文摘要
The Generalized Kadanoff--Baym Ansatz with mean-field propagators is increasingly used to simulate non-equilibrium quantum fermionic and bosonic systems. Compared with the full Kadanoff--Baym equations, its mean-field propagators substantially reduce computational cost, enabling simulations with computational effort that scales linearly with propagation time. However, the time-diagonal structure of the Generalized Kadanoff--Baym Ansatz obscures spectral properties within the collision integral of the transport equation. Here, we recover and investigate these hidden spectral properties using the extended Generalized Kadanoff--Baym Ansatz. For a Hubbard cluster, we compare ground-state spectral functions obtained with the extended Generalized Kadanoff--Baym Ansatz against those from standard Kadanoff--Baym equations. At moderate interaction strengths, the spectral functions show good agreement. At large interaction strengths, however, significant deviations emerge, and the spectral function obtained with the extended Generalized Kadanoff--Baym Ansatz becomes negative. These results demonstrate that, despite its computational advantages, the Generalized Kadanoff--Baym Ansatz has important limitations in strongly interacting regimes and may produce unphysical spectral properties when interactions become sufficiently large.
