Taming the cosmological constant in 2D causal quantum gravity with topology change

TL;DR

This paper analytically solves the quantum dynamics of 2D causal quantum gravity with topology change, showing that microscopic wormholes can reduce the effective cosmological constant without requiring fundamental discreteness.

Contribution

It provides a complete analytical solution of 2D causal quantum gravity with topology change, demonstrating a mechanism for cosmological constant suppression via wormholes.

Findings

Infinitesimal wormholes decrease the effective cosmological constant.

Finite microscopic wormhole density is obtained without assuming discreteness.

The model supports a well-defined gravitational path integral with topology sum under causality restrictions.

Abstract

As shown in previous work, there is a well-defined nonperturbative gravitational path integral including an explicit sum over topologies in the setting of Causal Dynamical Triangulations in two dimensions. In this paper we derive a complete analytical solution of the quantum continuum dynamics of this model, obtained uniquely by means of a double-scaling limit. We show that the presence of infinitesimal wormholes leads to a decrease in the effective cosmological constant, reminiscent of the suppression mechanism considered by Coleman and others in the four-dimensional Euclidean path integral. Remarkably, in the continuum limit we obtain a finite spacetime density of microscopic wormholes without assuming fundamental discreteness. This shows that one can in principle make sense of a gravitational path integral which includes a sum over topologies, provided suitable causality restrictions are imposed on the path integral histories.