Second- and First-Order Phase Transitions in CDT

TL;DR

This paper investigates phase transitions in Causal Dynamical Triangulations (CDT), providing evidence for first- and second-order transitions, which are crucial for understanding quantum gravity at the Planck scale.

Contribution

It offers the first detailed numerical analysis of phase transition orders in 4D CDT, highlighting the significance of second-order transitions for quantum gravity.

Findings

A-C transition is first order.

B-C transition is second order.

Second-order transition may relate to ultraviolet fixed points.

Abstract

Causal Dynamical Triangulations (CDT) is a proposal for a theory of quantum gravity, which implements a path-integral quantization of gravity as the continuum limit of a sum over piecewise flat spacetime geometries. We use Monte Carlo simulations to analyse the phase transition lines bordering the physically interesting de Sitter phase of the four-dimensional CDT model. Using a range of numerical criteria, we present strong evidence that the so-called A-C transition is first order, while the B-C transition is second order. The presence of a second-order transition may be related to an ultraviolet fixed point of quantum gravity and thus provide the key to probing physics at and possibly beyond the Planck scale.