arXiv subjects

Julien Dubédat

Publications and source records attributed to Julien Dubédat.

14 recordsLinked to original sources

arXiv2022

Metric growth dynamics in Liouville quantum gravity

We consider the metric growth in Liouville quantum gravity (LQG) for $γ\in (0,2)$. We show that a process associated with the trace of the free field on the boundary of a filled LQG ball is stationary, for every $γ\in (0,2)$. The infinitesimal version of this stationarity combined with an explicit expression of the generator of the evolution of the trace field $(h_t)$ provides a formal invariance equation that a measure on trace fields must satisfy. When considering a modified process corresponding to an evolution of LQG surfaces, we prove that the invariance equation is satisfied by an explicit $σ$-finite measure on trace fields. This explicit measure on trace fields only corresponds to the pure gravity case. On the way to prove this invariance, we retrieve the specificity of both $γ= \sqrt{8/3}$ and of the LQG dimension $d_γ = 4$. In this case, we derive an explicit expression of the (nonsymmetric) Dirichlet form associated with the process $(h_t)$ and construct dynamics associated with its symmetric part.

math.PR↗

arXiv2022

Random clusters in the Villain and XY models

In the Ising and Potts model, random cluster representations provide a geometric interpretation to spin correlations. We discuss similar constructions for the Villain and XY models, where spins take values in the circle, as well as extensions to models with different single site spin spaces. In the Villain case, we highlight natural interpretation in terms of the cable system extension of the model. We also list questions and open problems on the cluster representations obtained in this fashion.

math.PR↗

arXiv2021

Stochastic Ricci Flow on Compact Surfaces

In this paper we introduce the stochastic Ricci flow (SRF) in two spatial dimensions. The flow is symmetric with respect to a measure induced by Liouville Conformal Field Theory. Using the theory of Dirichlet forms, we construct a weak solution to the associated equation of the area measure on a flat torus, in the full "$L^1$ regime" $σ< σ_{L^1}=2\sqrtπ$ where $σ$ is the noise strength. We also describe the main necessary modifications needed for the SRF on general compact surfaces, and list some open questions.

math.PR↗

arXiv2020

Tightness of Liouville first passage percolation for $γ\in (0,2)$

We study Liouville first passage percolation metrics associated to a Gaussian free field $h$ mollified by the two-dimensional heat kernel $p_t$ in the bulk, and related star-scale invariant metrics. For $γ\in (0,2)$ and $ξ= \fracγ{d_γ}$, where $d_γ$ is the Liouville quantum gravity dimension defined in [Ding-Gwynne18], we show that renormalized metrics $(λ_t^{-1} e^{ξp_t * h} ds)_{t \in (0,1)}$ are tight with respect to the uniform topology. In particular, we show that subsequential limits are bi-Hölder with respect to the Euclidean topology, obtain tail estimates for side-to-side distances and derive error bounds for the normalizing constants $λ_t$.

math.PR↗

arXiv2020

Weak LQG metrics and Liouville first passage percolation

For $γ\in (0,2)$, we define a weak $γ$-Liouville quantum gravity (LQG) metric to be a function $h\mapsto D_h$ which takes in an instance of the planar Gaussian free field (GFF) and outputs a metric on the plane satisfying a certain list of natural axioms. We show that these axioms are satisfied for any subsequential limits of Liouville first passage percolation. Such subsequential limits were proven to exist by Ding-Dubédat-Dunlap-Falconet (2019). It is also known that these axioms are satisfied for the $\sqrt{8/3}$-LQG metric constructed by Miller and Sheffield (2013-2016). For any weak $γ$-LQG metric, we obtain moment bounds for diameters of sets as well as point-to-point, set-to-set, and point-to-set distances. We also show that any such metric is locally bi-Hölder continuous with respect to the Euclidean metric and compute the optimal Hölder exponents in both directions. Finally, we show that LQG geodesics cannot spend a long time near a straight line or the boundary of a metric ball. These results are used in subsequent work by Gwynne and Miller which proves that the weak $γ$-LQG metric is unique for each $γ\in (0,2)$, which in turn gives the uniqueness of the subsequential limit of Liouville first passage percolation. However, most of our results are new even in the special case when $γ=\sqrt{8/3}$.

math.PR↗

arXiv2019

Liouville metric of star-scale invariant fields: tails and Weyl scaling

We study the Liouville metric associated to an approximation of a log-correlated Gaussian field with short range correlation. We show that below a parameter $γ_c >0$, the left-right length of rectangles for the Riemannian metric $e^{γϕ_{0,n}} ds^2$ with various aspect ratio is concentrated with quasi-lognormal tails, that the renormalized metric is tight when $γ< \min ( γ_c, 0.4)$ and that subsequential limits are consistent with the Weyl scaling.

math.PR↗

arXiv2015

An SLE$_2$ loop measure

There is an essentially unique way to associate to any Riemann surface a measure on its simple loops, such that the collection of measures satisfy a strong conformal invariance property. Wendelin Werner constructed these random simple loops as boundaries of Brownian loops, and so they correspond in the zoo of statistical mechanics models to central charge $0$, or Schramm-Loewner Evolution (SLE) parameter $κ=8/3$. The goal of this paper is to construct a family of measures on simple loops on Riemann surfaces that satisfies a conformal covariance property, and that would correspond to SLE parameter $κ=2$ (central charge $-2$). On planar annuli, this loop measure was already built by Adrien Kassel and Rick Kenyon. We will give an alternative construction of this loop measure on planar annuli, investigate its conformal covariance, and finally extend this measure to general Riemann surfaces. This gives an example of a Malliavin-Kontsevich-Suhov loop measure in non-zero central charge.

math.PR↗

arXiv2014

Asymptotics of height change on toroidal Temperleyan dimer models

The dimer model is an exactly solvable model of planar statistical mechanics. In its critical phase, various aspects of its scaling limit are known to be described by the Gaussian free field. For periodic graphs, criticality is an algebraic condition on the spectral curve of the model, determined by the edge weights; isoradial graphs provide another class of critical dimer models, in which the edge weights are determined by the local geometry. In the present article, we consider another class of graphs: general Temperleyan graphs, i.e. graphs arising in the (generalized) Temperley bijection between spanning trees and dimer models. Building in particular on Forman's formula and representations of Laplacian determinants in terms of Poisson operators, and under a minimal assumption - viz. that the underlying random walk converges to Brownian motion - we show that the natural topological observable on macroscopic tori converges in law to its universal limit, i.e. the law of the periods of the dimer height function converges to that of the periods of a compactified free field.

math.PR↗

arXiv2014

SLE and Virasoro representations: localization

We consider some probabilistic and analytic realizations of Virasoro highest-weight representations. Specifically, we consider measures on paths connecting points marked on the boundary of a (bordered) Riemann surface. These Schramm-Loewner Evolution (SLE)- type measures are constructed by the method of localization in path space. Their partition function (total mass) is the highest-weight vector of a Virasoro representation, and the action is given by Virasoro uniformization. We review the formalism of Virasoro uniformization, which allows to define a canonical action of Virasoro generators on functions (or sections) on a - suitably extended - Teichmüller space. Then we describe the construction of families of measures on paths indexed by marked bordered Riemann surfaces. Finally we relate these two notions by showing that the partition functions of the latter generate a highest-weight representation - the quotient of a reducible Verma module - for the former.

math.PR↗

arXiv2014

SLE and Virasoro representations: Fusion

We continue the study of null-vector equations in relation with partition functions of (systems of) Schramm-Loewner Evolutions (SLEs) by considering the question of fusion. Starting from $n$ commuting SLEs seeded at distinct points, the partition function satisfies $n$ null-vector equations (at level 2). We show how to obtain higher level null-vector equations by coalescing the seeds one by one. As an example, we extend Schramm's formula (for the position of a marked bulk point relatively to a chordal SLE trace) to an arbitrary number of SLE strands. The argument combines input from representation theory - the study of Verma modules for the Virasoro algebra - with regularity estimates, themselves based on hypoellipticity and stochastic flow arguments.

math.PR↗

arXiv2014

Dimers and analytic torsion I

In the dimer model, a configuration consists of a perfect matching of a fixed graph. If the underlying graph is planar and bipartite, such a configuration is associated to a height function. For appropriate "critical" (weighted) graphs, this height function is known to converge in the fine mesh limit to a Gaussian free field, following in particular Kenyon's work. In the present article, we study the asymptotics of smoothed and local field observables from the point of view of families of Cauchy-Riemann operators and their determinants. This allows in particular to obtain a functional invariance principle for the field; characterise completely the limiting field on toroidal graphs as a compactified free field; analyse electric correlators; and settle the Fisher-Stephenson conjecture on monomer correlators. The analysis is based on comparing the variation of determinants of families of (continuous) CR operators with that of their discrete (finite dimensional) approximations. This relies in turn on estimating precisely inverting kernels, in particular near singularities. In order to treat correlators of "singular" local operators, elements of (multiplicatively) multi-valued discrete holomorphic functions are discussed.

math.PR↗

arXiv2014

Double dimers, conformal loop ensembles and isomonodromic deformations

The double-dimer model consists in superimposing two independent, identically distributed perfect matchings on a planar graph, which produces an ensemble of non-intersecting loops. Kenyon established conformal invariance in the small mesh limit by considering topological observables of the model parameterized by $\SL_2(\C)$ representations of the fundamental group of the punctured domain. The scaling limit is conjectured to be $\CLE_4$, the Conformal Loop Ensemble at $κ=4$. In support of this conjecture, we prove that a large subclass of these topological correlators converge to their putative $\CLE_4$ limit. Both the small mesh limit of the double-dimer correlators and the corresponding $\CLE_4$ correlators are identified in terms of the $τ$-functions introduced by Jimbo, Miwa and Ueno in the context of isomonodromic deformations.

math.PR↗

arXiv2011

Exact bosonization of the Ising model

We present exact combinatorial versions of bosonization identities, which equate the product of two Ising correlators with a free field (bosonic) correlator. The role of the discrete free field is played by the height function of an associated bipartite dimer model. Some applications to the asymptotic analysis of Ising correlators are discussed.

math.PR↗

arXiv2011

Topics on abelian spin models and related problems

In these notes, we discuss a selection of topics on several models of planar statistical mechanics. We consider the Ising, Potts, and more generally abelian spin models; the discrete Gaussian free field; the random cluster model; and the six-vertex model. Emphasis is put on duality, order, disorder and spinor variables, and on mappings between these models.

math.PR↗