Unitarity, stability, and loops of unstable ghosts
Unitarity, stability, and loops of unstable ghosts
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DOI：
10.1103/physrevd.100.105006
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发表时间：
2019-11-12
影响因子：
5
通讯作者：
Menezes, Gabriel
中科院分区：
文献类型：
--
作者：
Donoghue, John F.;Menezes, Gabriel
我们对二次引力理论和Lee-Wick型理论中出现的不稳定幽灵共振提出了新的认识。量子修正使这种共振不稳定，因此它不会出现在渐近谱中。我们证明了这些理论对所有阶都是酉的。统一性通过在统一性和中只包含稳定状态的切来满足。这消除了将其视为统一和中的幽灵状态的需要。然而，我们经常使用窄宽度近似，其中我们确实包括了不稳定状态的切割，而忽略了稳定衰变产物的切割。如果我们在一个环路上用不稳定的幽灵共振来做这个，我们只有使用最初由Lee和Wick定义的轮廓才能得到正确的答案。量子效应也在费曼和延迟传播体中提供阻尼，导致扰动下的稳定性。
We present a new understanding of the unstable ghostlike resonance which appears in theories such as quadratic gravity and Lee-Wick type theories. Quantum corrections make this resonance unstable, such that it does not appear in the asymptotic spectrum. We prove that these theories are unitary to all orders. Unitarity is satisfied by the inclusion of only cuts from stable states in the unitarity sum. This removes the need to consider this as a ghost state in the unitarity sum. However, we often use a narrow-width approximation where we do include cuts through unstable states and ignore cuts through the stable decay products. If we do this with the unstable ghost resonance at one loop, we get the correct answer only by using a contour which was originally defined by Lee and Wick. The quantum effects also provide damping in both the Feynman and the retarded propagators, leading to stability under perturbations.