Continuum Random Combs and Scale Dependent Spectral Dimension

TL;DR

This paper introduces a simple analytical model using random combs to demonstrate how the effective spectral dimension of spacetime varies with scale, mimicking features observed in quantum gravity models.

Contribution

It develops a scale-dependent spectral dimension framework within random comb models, extending previous work and providing analytical insight into UV-IR dimensional crossover.

Findings

Spectral dimension decreases at small scales (UV) compared to large scales (IR).

A hierarchy of apparent spectral dimensions emerges in the crossover region.

Model validity extends to a wide class of tooth length distributions.

Abstract

Numerical computations have suggested that in causal dynamical triangulation models of quantum gravity the effective dimension of spacetime in the UV is lower than in the IR. In this paper we develop a simple model based on previous work on random combs, which share some of the properties of CDT, in which this effect can be shown to occur analytically. We construct a definition for short and long distance spectral dimensions and show that the random comb models exhibit scale dependent spectral dimension defined in this way. We also observe that a hierarchy of apparent spectral dimensions may be obtained in the cross-over region between UV and IR regimes for suitable choices of the continuum variables. Our main result is valid for a wide class of tooth length distributions thereby extending previous work on random combs by Durhuus et al.