Jose Navarro-Salas (University of Valencia)

"Ultraviolet regularity, CPT and the Big Bang quantum vacuum"

Abstract: In a general spacetime, there is no preferred choice of a vacuum state. In a cosmological scenario, this question translates to asking about how to select the initial quantum state. This issue is of major relevance since physical predictions depend upon the fixing of the initial vacuum. For instance, the main predictions of inflationary cosmology rely on the choice of the initial quantum state at the onset of inflation. Another example concerns the recent proposal [Boyle, Finn and Turok] for a CPT-symmetric cosmology in which the gravitational background is assumed to be time-reversal symmetric with respect to the big bang event. In this talk we will provide a simple characterization of the CPT-invariant vacuum states by naturally setting invariant initial conditions at the big bang. We will further impose ultraviolet regularity. The existence of many CPT-invariant vacua is somewhat analogous to the invariant $alpha$-vacua in de Sitter space. However, while the $alpha$-vacua are not ultraviolet regular, up to the Bunch-Davies vacuum, we identify several examples of CPT-invariant and ultraviolet regular vacuum states.