Manifestly causal in-in perturbation theory about the interacting vacuum
Manifestly causal in-in perturbation theory about the interacting vacuum
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DOI：
10.1007/jhep03(2021)080
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发表时间：
2020-10
影响因子：
5.4
通讯作者：
M. Baumgart;R. Sundrum
中科院分区：
文献类型：
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作者：
M. Baumgart;R. Sundrum
内外摄动理论是宇宙学和非平衡物理的重要工具。在这里，我们调和了与德西特/暴胀背景特别相关的两个重要方面之间的明显冲突：(i)需要用一个将自由（“束-戴维斯”）真空投射到相互作用真空上并使顶点积分定义良好的iλ处方稍微变形幺正时间演化；（ii） Weinberg对in-in摄动理论的“嵌套换向子”重新表述，在假设精确统一的情况下，表明局部算子期望值内因果关系的约束。我们证明了一个修正的iλ处方保持了（ii）的推导所依赖的精确的统一性，而对于所有阶的摄动理论，它都非平凡地与(i)一致。
In-In perturbation theory is a vital tool for cosmology and nonequilibrium physics. Here, we reconcile an apparent conflict between two of its important aspects with particular relevance to De Sitter/inflationary contexts:(i) the need to slightly deform unitary time evolution with an iϵ prescription that projects the free (“Bunch-Davies”) vacuum onto the interacting vacuum and renders vertex integrals well-defined, and (ii) Weinberg’s “nested commutator” reformulation of in-in perturbation theory which makes manifest the constraints of causality within expectation values of local operators, assuming exact unitarity. We show that a modified iϵ prescription maintains the exact unitarity on which the derivation of (ii) rests, while nontrivially agreeing with (i) to all orders of perturbation theory.