Vacuum prescription for inflationary in-in integrals
= Vacuum prescription for inflationary in-in integrals
{title2=$\tau_i=-\infty(1-i\varepsilon),\quad\varepsilon>0$}
The Gaussian <Bunch-Davies vacuum> is selected by tilting the early endpoint to $-\infty(1-i\varepsilon)$ for integrands $e^{iK\tau}$ with $K>0$. They then decay at the early boundary. The complex-conjugate integrand requires the opposite tilt. Ordered contractions and their contour must be conjugated together.