追踪宇宙学中的大质量场
Tracing out massive fields in cosmology
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中文总结 AI 辅助
本研究通过in-in形式论和约化密度矩阵，探讨了德西特空间中积分掉大质量场对光场关联函数的影响，并验证了有效描述与完整理论的一致性。
中文摘要 AI 辅助
宇宙学关联函数通过（准）德西特背景下的in-in形式论进行计算。其有效描述最好用约化密度矩阵来表示。在这项工作中，我们研究了在德西特空间中积分掉一个大质量场如何决定一个光场在有限观测时间下的约化密度矩阵。从一个具有非线性耦合的准单场模型出发，我们首先在固定的最终值下评估大质量场的波泛函，然后对该值进行求迹。该求迹产生了通常在Schwinger--Keldysh描述中存在的分支混合项。对于一个共形耦合的大质量场，我们明确展示了来自有效描述的光场双谱与完整理论计算一致。这个例子还表明，场在未来边界处的衰减本身并不能证明将其对求迹的贡献丢弃是合理的。我们讨论了精确的非局部有效描述与通过大质量展开获得的局部有效场论之间的差异。然后我们识别出哪些局部三次项影响晚期概率，哪些仅贡献波泛函相位。最后，我们根据响应、噪声和Schwinger--Keldysh一致性条件对所得核进行组织，并讨论约化密度矩阵的对称性约束。
英文摘要
Cosmological correlators are calculated through the in-in formalism in (quasi-)de Sitter background. Its effective description is best represented by a reduced density matrix. In this work, we study how integrating out a massive field in de Sitter space determines the reduced density matrix of a light field at a finite observation time. Starting from a quasi-single-field model with non-linear couplings, we first evaluate the massive field wavefunctional at fixed final value and then trace over this value. The trace generates branch-mixing terms which are generally present in the Schwinger--Keldysh description. For a conformally coupled massive field, we show explicitly that the light field bispectrum from the effective description agrees with a full theory calculation. This example also shows that decay of a field at the future boundary does not by itself justify discarding its contribution to the trace. We discuss the differences between an exact nonlocal effective description and the local effective field theory obtained through a large mass expansion. We then identify which local cubic terms affect the late-time probability and which contribute only a wavefunctional phase. Finally, we organize the resulting kernels by response, noise, and Schwinger--Keldysh consistency conditions, and discuss the symmetry constraints on the reduced density matrix.
发表机构
- Chongqing University（重庆大学）
- City University of Hong Kong（香港城市大学）
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