Menagerie of Euclidean constructions for 3D holographic cosmologies

TL;DR

This paper develops a method to generate numerous exact solutions in 3D gravity with matter, extending previous models to include more complex cosmologies and analyzing their dominance in the Euclidean path integral.

Contribution

It introduces a generalized construction of 3D gravity solutions with baby universe cosmologies and AdS tubes, expanding the class of known holographic models.

Findings

Constructed a large class of exact 3D gravity solutions with cosmological features.

Identified conditions under which these solutions dominate the Euclidean path integral.

Compared new solutions with previous models and discussed dominance criteria.

Abstract

We construct a large number of exact solutions of three-dimensional gravity with heavy matter particles that generalize the construction of Antonini, Sasieta, and Swingle (AS${}^2$), argued to define CFT states dual to a spacetime with a closed baby universe cosmology. Our construction starts with an arbitrary heavy-particle closed universe cosmology of the type constructed in Maloney, Meruliya, and Van Raamsdonk [arXiv:2503.12227], and via a gluing procedure adds an arbitrary number of AdS tubes connecting the past and future conformal boundaries of the associated Euclidean wormhole solution. With our construction, it is straightforward to produce examples where the cosmology is approximately homogeneous and isotropic. We describe a necessary condition for the cosmological wormhole saddle to dominate the Euclidean path integral with the specified boundary conditions. We argue that the original AS${}^2$ construction usually does not meet this condition, and describe alternative saddles that are likely to dominate. We discuss various possibilities for how the cosmological saddle might be made to dominate in our generalized construction.