Cosmological bulk-to-boundary propagator
= Cosmological bulk-to-boundary propagator
For a free mode function $f(k,\eta)$ and a correlator evaluated at $\eta_0$, the two cosmological bulk-to-boundary propagators are $K_R=f(k,\eta)f^*(k,\eta_0)$ and $K_L=f^*(k,\eta)f(k,\eta_0)$, up to the chosen contour-label convention.