Noise kernels of stochastic gravity in conformally-flat spacetimes

The central object in the theory of semiclassical stochastic gravity is the noise kernel, which is the symmetric two point correlation function of the stress–energy tensor. Using the corresponding Wightman functions in Minkowski, Einstein and open Einstein spaces, we construct the noise kernels of a conformally coupled scalar field in these spacetimes. From them we show that the noise kernels in conformally-flat spacetimes, including the Friedmann–Robertson–Walker universes, can be obtained in closed analytic forms by using a combination of conformal and coordinate transformations. (paper)