Numerical prescriptions of early-time divergences of the in-in formalism

Understand

In quantum field theory, the in and out states can be related to the full Hamiltonian by the $i\epsilon$ prescription.

• A Wick rotation can further bring the correlation functions to Euclidean spacetime where the integrals are better defined.
• This setup is convenient for analytical calculations.
• However, for numerical calculations, an infinitesimal $\epsilon$ or a Wick rotation of numerical functions are difficult to implement.