Semiclassical Physics in gravitational scenario, in its first approximation (1st order) cares only for the expectation value of stress energy tensor and ignores the inherent quantum fluctuations thereof. In the approach of stochastic gravity, on the other hand, these matter fluctuations are supposed to work as the source of geometry fluctuations and have the potential to render the results from 1st order semiclassical physics irrelevant. We study the object of central significance in stochastic gravity, i.e. the noise kernel, for a wide class of Friedmann space-times. Through an equivalence of quantum fields on de Sitter space-time and those on generic Friedmann universes, we obtain the noise kernel through the correlators of Stress Energy Tensor (SET) for fixed co-moving but large physical distances. We show that in many Friedmann universes including the expanding universes, the initial quantum fluctuations, the universe is born with, may remain invariant and important even at late times. Further, we explore the cosmological space-times where even after long times the quantum fluctuations remain strong and become dominant over large physical distances, which the matter driven universe is an example of. The study is carried out in minimal as well as non-minimal interaction settings. Implications of such quantum fluctuations are discussed.

中文翻译：

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de Sitter时空中的应力能相关器：在连接的Friedmann宇宙中其共形掩蔽或增长

引力场景中的半经典物理学在其第一近似（一阶）中仅关注应力能张量的期望值，而忽略了其固有的量子涨落。另一方面，在随机引力的方法中，这些物质涨落被认为是几何涨落的来源，并且有可能使一阶半经典物理学的结果变得无关紧要。我们研究了广泛的弗里德曼时空中随机引力具有中心意义的对象，即噪声核。通过等效于de Sitter时空和通用Friedmann宇宙上的量子场，我们通过应力能量张量（SET）的相关器获得了固定运动的但较大物理距离的噪声核。我们表明，在包括扩展宇宙在内的许多弗里德曼宇宙中，宇宙所固有的初始量子涨落即使在后期也可能保持不变且重要。此外，我们探索宇宙时空，即使长时间后，量子涨落仍保持强势并在较大的物理距离上占主导地位，这是物质驱动宇宙的一个例子。该研究是在最小交互设置和非最小交互设置下进行的。讨论了这种量子涨落的含义。物质驱动的宇宙就是一个例子。该研究是在最小交互设置和非最小交互设置下进行的。讨论了这种量子涨落的含义。物质驱动的宇宙就是一个例子。该研究是在最小交互设置和非最小交互设置下进行的。讨论了这种量子涨落的含义。