  General relativity predicts final-type singularities inside black holes, as
well as a cosmological initial-type singularity. Cosmic censorship protects
external observers from black hole singularities, while Penrose's Weyl
curvature hypothesis protects the smoothness of the initial (Big Bang)
singularity. We discuss a simple realization of the Weyl curvature hypothesis
by assuming a very early radiation-dominated universe and analytically
extending the expansion factor to negative values of conformal time. We impose
time-reversal conditions at the Big Bang to characterize a natural set of
preferred vacuum states for quantized matter fields. We implement the
prescription of States of Low Energy constructed around the Big Bang obtaining
Hadamard states. We also explore the physical implications of these vacua for
cosmological dark matter production.

General Relativity and Quantum Cosmology;High Energy Physics - Theory