De Sitter Bra-Ket Wormholes

TL;DR

This paper explores a gravitational path integral approach to the universe's initial state using connected geometries in Lorentzian de Sitter gravity, revealing a probabilistic distribution that dominates over traditional models but lacks normalization.

Contribution

It introduces a novel connected geometry framework for the initial state in de Sitter gravity, incorporating matter fields and analyzing probabilistic interpretations.

Findings

Connected geometries dominate over Hartle-Hawking saddle in large universes

The resulting distribution has a meaningful probabilistic interpretation for local observables

The distribution is non-normalizable over the entire phase space

Abstract

We study a model for the initial state of the universe based on a gravitational path integral that includes connected geometries which simultaneously produce bra and ket of the wave function. We argue that a natural object to describe this state is the Wigner distribution, which is a function on a classical phase space obtained by a certain integral transform of the density matrix. We work with Lorentzian de Sitter Jackiw-Teitelboim gravity in which we find semiclassical saddle-points for pure gravity, as well as when we include matter components such as a CFT and a classical inflaton field. We also discuss different choices of fixing time reparametrizations. In the regime of large universes our connected geometry dominates over the Hartle-Hawking saddle and gives a distribution that has a meaningful probabilistic interpretation for local observables. It does not, however, give a normalizable probability measure on the entire phase space of the theory.