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

R. Loll·W. Westra·S. Zohren
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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.

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R. Loll, W. Westra, S. Zohren. 2006-06-27. Taming the cosmological constant in 2D causal quantum gravity with topology change. https://doi.org/10.1016/j.nuclphysb.2006.06.033

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