arXiv subjects

Timothy Budd

Publications and source records attributed to Timothy Budd.

25 records · Page 2Linked to original sources

arXiv2017

Geometry of infinite planar maps with high degrees

We study the geometry of infinite random Boltzmann planar maps with vertices of high degree. These correspond to the duals of the Boltzmann maps associated to a critical weight sequence $(q_{k})_{ k \geq 0}$ for the faces with polynomial decay $k^{-a}$ with $a \in ( 3/2, 5/2)$ which have been studied by Le Gall & Miermont as well as by Borot, Bouttier & Guitter. We show the existence of a phase transition for the geometry of these maps at $a = 2$. In the dilute phase corresponding to $a \in (2, 5/2)$ we prove that the volume of the ball of radius $r$ (for the graph distance) is of order $r^{\mathsf{d}}$ with $\mathsf{d}= (a-1/2)/(a-2)$, and we provide distributional scaling limits for the volume and perimeter process. In the dense phase corresponding to $a \in (3/2,2)$ the volume of the ball of radius $r$ is exponential in $r$. We also study the first-passage percolation (FPP) distance with exponential edge weights and show in particular that in the dense phase the FPP distance between the origin and infinity is finite. The latter implies in addition that the random lattices in the dense phase are transient. The proofs rely on the recent peeling process introduced in arXiv:1506.01590 and use ideas of arXiv:1412.5509 in the dilute phase.

math.PR↗

arXiv2016

The peeling process of infinite Boltzmann planar maps

We start by studying a peeling process on finite random planar maps with faces of arbitrary degrees determined by a general weight sequence, which satisfies an admissibility criterion. The corresponding perimeter process is identified as a biased random walk, in terms of which the admissibility criterion has a very simple interpretation. The finite random planar maps under consideration were recently proved to possess a well-defined local limit known as the infinite Boltzmann planar map (IBPM). Inspired by recent work of Curien and Le Gall, we show that the peeling process on the IBPM can be obtained from the peeling process of finite random maps by conditioning the perimeter process to stay positive. The simplicity of the resulting description of the peeling process allows us to obtain the scaling limit of the associated perimeter and volume process for arbitrary regular critical weight sequences.

math-ph↗

arXiv2015

Multi-point functions of weighted cubic maps

We study the geodesic two- and three-point functions of random weighted cubic maps, which are obtained by assigning random edge lengths to random cubic planar maps. Explicit expressions are obtained by taking limits of recently established bivariate multi-point functions of general planar maps. We give an alternative interpretation of the two-point function in terms of an Eden model exploration process on a random planar triangulation. Finally, the scaling limits of the multi-point functions are studied, showing in particular that the two- and three-point functions of the Brownian map are recovered as the number of faces is taken to infinity.

math-ph↗

arXiv2014

Geodesic distances in Liouville quantum gravity

In order to study the quantum geometry of random surfaces in Liouville gravity, we propose a definition of geodesic distance associated to a Gaussian free field on a regular lattice. This geodesic distance is used to numerically determine the Hausdorff dimension associated to shortest cycles of 2d quantum gravity on the torus coupled to conformal matter fields, showing agreement with a conjectured formula by Y. Watabiki. Finally, the numerical tools are put to test by quantitatively comparing the distribution of lengths of shortest cycles to the corresponding distribution in large random triangulations.

hep-th↗

arXiv2013

The toroidal Hausdorff dimension of 2d Euclidean quantum gravity

The lengths of shortest non-contractible loops are studied numerically in 2d Euclidean quantum gravity on a torus coupled to conformal field theories with central charge less than one. We find that the distribution of these geodesic lengths displays a scaling in agreement with a Hausdorff dimension given by the formula of Y. Watabiki.

hep-th↗

arXiv2011

The effective kinetic term in CDT

We report on recently performed simulations of Causal Dynamical Triangulations (CDT) in 2+1 dimensions aimed at studying its effective dynamics in the continuum limit. Two pieces of evidence from completely different measurements are presented suggesting that three-dimensional CDT is effectively described by an action with kinetic term given by a modified Wheeler-De Witt metric. These observations could strengthen an earlier observed connection between CDT and Horava-Lifshitz gravity. One piece of evidence comes from measurements of the modular parameter in CDT simulations with spatial topology of a torus, the other from measurements of local metric fluctuations close to a fixed spatial boundary.

gr-qc↗

arXiv2011

Shape Dynamics in 2+1 Dimensions

Shape Dynamics is a formulation of General Relativity where refoliation invariance is traded for local spatial conformal invariance. In this paper we explicitly construct Shape Dynamics for a torus universe in 2+1 dimensions through a linking gauge theory that ensures dynamical equivalence with General Relativity. The Hamiltonian we obtain is formally a reduced phase space Hamiltonian. The construction of the Shape Dynamics Hamiltonian on higher genus surfaces is not explicitly possible, but we give an explicit expansion of the Shape Dynamics Hamiltonian for large CMC volume. The fact that all local constraints are linear in momenta allows us to quantize these explicitly, and the quantization problem for Shape Dynamics turns out to be equivalent to reduced phase space quantization. We consider the large CMC-volume asymptotics of conformal transformations of the wave function. We then use the similarity of Shape Dynamics on the 2-torus with the explicitly constructible strong gravity (BKL) Shape Dynamics Hamiltonian in higher dimensions to suggest a quantization strategy for Shape Dynamics.

gr-qc↗