A Note on the Existence of Equal Time Correlators

The Schroedinger picture, which underpins the Wavefunction of the Universe framework to compute Cosmological Correlators, is known to be generically problematic in QFT because of the required infinite localization of the fields in time. We study under which conditions momentum space equal time correlators of scalar fields are finite in flat space. We identify cases where they can be divergent even after renormalizing the theory, while also providing sufficient conditions for their existence. Concrete examples are discussed, covering the well known $\lambda {\phi }^4$ model, composite operators and effective field theories.