arXiv subjects

Naotaka Kajino

Publications and source records attributed to Naotaka Kajino.

16 recordsLinked to original sources

arXiv2026

Contraction properties and differentiability of $p$-energy forms with applications to nonlinear potential theory on self-similar sets

We introduce a new contraction property, which we call the generalized $p$-contraction property, for $p$-energy forms as generalizations of many well-known inequalities, such as $p$-Clarkson's inequality, the strong subadditivity and the Markov property in the theory of nonlinear Dirichlet forms, and show that any $p$-energy form satisfying $p$-Clarkson's inequality is Fréchet differentiable. We also verify the generalized $p$-contraction property for $p$-energy forms on fractals constructed by Kigami [Mem. Eur. Math. Soc. 5 (2023)] and by Cao--Gu--Qiu [Adv. Math. 405 (2022), no. 108517]. As a general framework of $p$-energy forms taking the generalized $p$-contraction property into consideration, we introduce the notion of $p$-resistance form and investigate fundamental properties of $p$-harmonic functions with respect to $p$-resistance forms. In particular, some new estimates on scaling factors of self-similar $p$-energy forms on self-similar sets are obtained by establishing Hölder regularity estimates for $p$-harmonic functions, and the $p$-walk dimensions of any generalized Sierpiński carpet and the $D$-dimensional level-$l$ Sierpiński gasket are shown to be strictly greater than $p$.

math.FA↗

arXiv2026

Two-sided heat kernel bounds for $\sqrt{8/3}$-Liouville Brownian motion

Liouville Brownian motion (LBM) is the canonical diffusion process on a Liouville quantum gravity (LQG) surface. In this work, we establish upper and lower bounds for the heat kernel for LBM when $γ=\sqrt{8/3}$ in terms of the $\sqrt{8/3}$-LQG metric which are sharp up to a polylogarithmic factor in the exponential.

math.PR↗

arXiv2026

Generalized Kac's moment formula for positive continuous additive functionals of Markov processes

We establish a formula for moments of certain random variables involving positive continuous additive functionals (PCAFs) of standard processes which have absolutely continuous transition functions and are in duality with standard processes with absolutely continuous transition functions,generalizing the classical Kac's moment formula. In particular, all our results are applicable to the more familiar case of symmetric Hunt processes which are associated with regular Dirichlet forms and have absolutely continuous transition functions.

math.PR↗

arXiv2025

Heat kernel estimates for boundary traces of reflected diffusions on uniform domains

We study the boundary trace processes of reflected diffusions on uniform domains. We obtain stable-like heat kernel estimates for such a boundary trace process when the diffusion on the underlying ambient space satisfies sub-Gaussian heat kernel estimates. Our arguments rely on new results of independent interest such as sharp two-sided estimates and the volume doubling property of the harmonic measure, the existence of a continuous extension of the Naïm kernel to the topological boundary, and the Doob--Naïm formula identifying the Dirichlet form of the boundary trace process as the pure-jump Dirichlet form whose jump kernel with respect to the harmonic measure is exactly (the continuous extension of) the Naïm kernel.

math.PR↗

arXiv2025

$p$-Energy forms on fractals: recent progress

In this article, we survey recent progress on self-similar $p$-energy forms on self-similar fractals, where $p\in(1,\infty)$. While for $p=2$ the notion of such forms coincides with that of self-similar Dirichlet forms and there have been plenty of studies on them since the late 1980s, studies on the case of $p\in(1,\infty)\setminus\{2\}$ was initiated much later in 2004 by Herman, Peirone and Strichartz [Potential Anal. 20 (2004), 125--148] and Strichartz and Wong [Nonlinearity 17 (2004), 595--616] and no essential progress on this case had been made since then until a few years ago. The recent progress by Kigami, Shimizu, Cao--Gu--Qiu and Murugan--Shimizu has established the existence of such $p$-energy forms on general post-critically finite (p.-c.f.) self-similar sets and on large classes of low-dimensional infinitely ramified self-similar sets, and the authors have proved further detailed properties of these forms and associated $p$-harmonic functions, mainly for p.-c.f. self-similar sets. This article is devoted to a review of these results, focusing on the most recent developments by the authors and illustrating them in the simplest non-trivial setting of the two-dimensional standard Sierpiński gasket.

math.FA↗

arXiv2024

Korevaar-Schoen $p$-energy forms and associated $p$-energy measures on fractals

We construct good $p$-energy forms on metric measure spaces as pointwise subsequential limits of Besov-type $p$-energy functionals under certain geometric/analytic conditions. Such forms are often called Korevaar-Schoen $p$-energy forms in the literature. As an advantage of our approach, the associated $p$-energy measures are obtained and investigated. We also prove that our construction is applicable to the settings of Kigami [Mem. Eur. Math. Soc. 5 (2023)] and Cao-Gu-Qiu [Adv. Math. 405 (2022), no. 108517], yields Korevaar-Schoen $p$-energy forms comparable to the $p$-energy forms constructed in these papers, and can be further modified in the case of self-similar sets to obtain self-similar $p$-energy forms keeping most of the good properties of Korevaar-Schoen ones.

math.FA↗

arXiv2022

On the conformal walk dimension: Quasisymmetric uniformization for symmetric diffusions

We introduce the notion of conformal walk dimension, which serves as a bridge between elliptic and parabolic Harnack inequalities. The importance of this notion is due to the fact that, for a given strongly local, regular symmetric Dirichlet space in which every metric ball has compact closure (MMD space), the finiteness of the conformal walk dimension characterizes the conjunction of the metric doubling property and the elliptic Harnack inequality. Roughly speaking, the conformal walk dimension of an MMD space is defined as the infimum over all possible values of the walk dimension with which the parabolic Harnack inequality can be made to hold by a time change of the associated diffusion and by a quasisymmetric change of the metric. We show that the conformal walk dimension of any MMD space satisfying the metric doubling property and the elliptic Harnack inequality is two, and provide a necessary condition for a pair of such changes to attain the infimum defining the conformal walk dimension when it is attained by the original pair. We also prove a necessary condition for the existence of such a pair attaining the infimum in the setting of a self-similar Dirichlet form on a self-similar set, and apply it to show that the infimum fails to be attained for the Vicsek set and the $N$-dimensional Sierpiński gasket with $N\geq 3$, in contrast to the attainment for the two-dimensional Sierpiński gasket due to Kigami [Math. Ann. 340 (2008), no. 4, 781--804].

math.PR↗

arXiv2022

An elementary proof that walk dimension is greater than two for Brownian motion on Sierpiński carpets

We give an elementary self-contained proof of the fact that the walk dimension of the Brownian motion on an arbitrary generalized Sierpiński carpet is greater than two, no proof of which in this generality had been available in the literature. Our proof is based solely on the self-similarity and hypercubic symmetry of the associated Dirichlet form and on several very basic pieces of functional analysis and the theory of regular symmetric Dirichlet forms. We also present an application of this fact to the singularity of the energy measures with respect to the canonical self-similar measure (uniform distribution) in this case, proved first by M. Hino in [Probab. Theory Related Fields 132 (2005), no. 2, 265-290].

math.PR↗

arXiv2021

On singularity of energy measures for symmetric diffusions with full off-diagonal heat kernel estimates II: Some borderline examples

We present a concrete family of fractals, which we call the (two-dimensional) thin scale irregular Sierpiński gaskets and each of which is equipped with a canonical strongly local regular symmetric Dirichlet form. We prove that any fractal $K$ in this family satisfies the full off-diagonal heat kernel estimates with some space-time scale function $Ψ_{K}$ and the singularity of the associated energy measures with respect to the canonical volume measure (uniform distribution) on $K$, and also that the decay rate of $r^{-2}Ψ_{K}(r)$ to $0$ as $r\downarrow 0$ can be made arbitrarily slow by suitable choices of $K$. These results together support the energy measure singularity dichotomy conjecture [Ann. Probab. 48 (2020), no. 6, 2920--2951, Conjecture 2.15] stating that, if the full off-diagonal heat kernel estimates with space-time scale function $Ψ$ satisfying $\lim_{r\downarrow 0}r^{-2}Ψ(r)=0$ hold for a strongly local regular symmetric Dirichlet space with complete metric, then the associated energy measures are singular with respect to the reference measure of the Dirichlet space.

math.PR↗

arXiv2021

The Laplacian on some self-conformal fractals and Weyl's asymptotics for its eigenvalues: A survey of the analytic aspects

This article surveys the analytic aspects of the author's recent studies on the construction and analysis of a "geometrically canonical" Laplacian on circle packing fractals invariant with respect to certain Kleinian groups (i.e., discrete groups of Möbius transformations on the Riemann sphere $\widehat{\mathbb{C}}=\mathbb{C}\cup\{\infty\}$), including the classical Apollonian gasket and some round Sierpiński carpets. The main result on Weyl's asymptotics for its eigenvalues is of the same form as that by Oh and Shah [Invent. Math. 187 (2012), 1--35, Theorem 1.4] on the asymptotic distribution of the circles in a very large class of such fractals.

math.PR↗

arXiv2020

Two-sided bounds on free energy of directed polymers on strongly recurrent graphs

We study the directed polymers in random environment on an infinite graph $G=(V,E)$ on which the underlying random walk satisfies sub-Gaussian heat kernel bounds with spectral dimension $d_{s}$ strictly less than two. Our goal in this paper is to show (i) the existence and the coincidence of the quenched and the annealed free energy $F_q(β)$, $F_a(β)$ and (ii) that $F_a(β)-F_q(β)$ is comparable to $β^{\frac{4}{2-d_{s}}}$ for small inverse temperature $β$.

math.PR↗

arXiv2020

On singularity of energy measures for symmetric diffusions with full off-diagonal heat kernel estimates

We show that for a strongly local, regular symmetric Dirichlet form over a complete, locally compact geodesic metric space, full off-diagonal heat kernel estimates with walk dimension strictly larger than two (\emph{sub-Gaussian} estimates) imply the singularity of the energy measures with respect to the symmetric measure, verifying a conjecture by M.\ T.\ Barlow in [Contemp.\ Math., vol.\ 338, 2003, pp.\ 11--40]. We also prove that in the contrary case of walk dimension two, i.e., where full off-diagonal \emph{Gaussian} estimates of the heat kernel hold, the symmetric measure and the energy measures are mutually absolutely continuous in the sense that a Borel subset of the state space has measure zero for the symmetric measure if and only if it has measure zero for the energy measures of all functions in the domain of the Dirichlet form.

math.PR↗

arXiv2020

The Laplacian on some self-conformal fractals and Weyl's asymptotics for its eigenvalues: A survey of the ergodic-theoretic aspects

This short survey is aimed at sketching the ergodic-theoretic aspects of the author's recent studies on Weyl's eigenvalue asymptotics for a \emph{"geometrically canonical" Laplacian} defined by the author on some self-conformal circle packing fractals including the classical \emph{Apollonian gasket}. The main result being surveyed is obtained by applying Kesten's renewal theorem [\emph{Ann.\ Probab.}\ \textbf{2} (1974), 355--386, Theorem 2] for functionals of Markov chains on general state spaces and provides an alternative probabilistic proof of the result by Oh and Shah [\emph{Invent.\ Math.}\ \textbf{187} (2012), 1--35, Corollary 1.8] on the asymptotic distribution of the circles in the Apollonian gasket.

math.DS↗

arXiv2017

Equivalence of recurrence and Liouville property for symmetric Dirichlet forms

Given a symmetric Dirichlet form $(\mathcal{E},\mathcal{F})$ on a (non-trivial) $σ$-finite measure space $(E,\mathcal{B},m)$ with associated Markovian semigroup $\{T_{t}\}_{t\in(0,\infty)}$, we prove that $(\mathcal{E},\mathcal{F})$ is both irreducible and recurrent if and only if there is no non-constant $\mathcal{B}$-measurable function $u:E\to[0,\infty]$ that is \emph{$\mathcal{E}$-excessive}, i.e., such that $T_{t}u\leq u$ $m$-a.e.\ for any $t\in(0,\infty)$. We also prove that these conditions are equivalent to the equality $\{u\in\mathcal{F}_{e}\mid \mathcal{E}(u,u)=0\}=\mathbb{R}\mathbf{1}$, where $\mathcal{F}_{e}$ denotes the extended Dirichlet space associated with $(\mathcal{E},\mathcal{F})$. The proof is based on simple analytic arguments and requires no additional assumption on the state space or on the form. In the course of the proof we also present a characterization of the $\mathcal{E}$-excessiveness in terms of $\mathcal{F}_{e}$ and $\mathcal{E}$, which is valid for any symmetric positivity preserving form.

math.PR↗

arXiv2015

Continuity and estimates of the Liouville heat kernel with applications to spectral dimensions

The Liouville Brownian motion (LBM), recently introduced by Garban, Rhodes and Vargas and in a weaker form also by Berestycki, is a diffusion process evolving in a planar random geometry induced by the Liouville measure $M_γ$, formally written as $M_γ(dz)=e^{γX(z)-{γ^2} \mathbb{E}[X(z)^2]/2}\, dz$, $γ\in(0,2)$, for a (massive) Gaussian free field $X$. It is an $M_γ$-symmetric diffusion defined as the time change of the two-dimensional Brownian motion by the positive continuous additive functional with Revuz measure $M_γ$. In this paper we provide a detailed analysis of the heat kernel $p_t(x,y)$ of the LBM. Specifically, we prove its joint continuity, a locally uniform sub-Gaussian upper bound of the form $p_t(x,y)\leq C_{1} t^{-1} \log(t^{-1}) \exp\bigl(-C_{2}((|x-y|^β\wedge 1)/t)^{\frac{1}{β-1}}\bigr)$ for $t\in(0,\frac{1}{2}]$ for each $β>\frac{1}{2}(γ+2)^2$, and an on-diagonal lower bound of the form $p_{t}(x,x)\geq C_{3}t^{-1}\bigl(\log(t^{-1})\bigr)^{-η}$ for $t\in(0,t_η(x)]$, with $t_η(x)\in(0,\frac{1}{2}]$ heavily dependent on $x$, for each $η>18$ for $M_γ$-almost every $x$. As applications, we deduce that the pointwise spectral dimension equals $2$ $M_γ$-a.e.\ and that the global spectral dimension is also $2$.

math.PR↗

arXiv2015

Localized upper bounds of heat kernels for diffusions via a multiple Dynkin-Hunt formula

We prove that for a general diffusion process, certain assumptions on its behavior \emph{only within a fixed open subset} of the state space imply the existence and sub-Gaussian type off-diagonal upper bounds of the \emph{global} heat kernel on the fixed open set. The proof is mostly probabilistic and is based on a seemingly new formula, which we call a \emph{multiple Dynkin-Hunt formula}, expressing the transition function of a Hunt process in terms of that of the part process on a given open subset. This result has an application to heat kernel analysis for the \emph{Liouville Brownian motion}, the canonical diffusion in a certain random geometry of the plane induced by a (massive) Gaussian free field.

math.PR↗