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Time Changes of the Brownian Motion: Poincaré Inequality, Heat Kernel Estimate and Protodistance

About this Title

Jun Kigami, Graduate School of Informatics, Kyoto University, Kyoto 606-8501, Japan

Publication: Memoirs of the American Mathematical Society
Publication Year: 2019; Volume 259, Number 1250
ISBNs: 978-1-4704-3620-9 (print); 978-1-4704-5255-1 (online)
DOI: https://doi.org/10.1090/memo/1250
Published electronically: April 18, 2019
Keywords: Sierpinski carpet, Brownian motion, time change, Poincaré inequality, protodistance, volume doubling property, walk dimension, heat kernel
MSC: Primary 31E05, 60J35, 60J60; Secondary 28A80, 30L10, 43A99, 60J65, 80A20

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Table of Contents

Chapters

  • 1. Introduction
  • 2. Generalized Sierpinski carpets
  • 3. Standing assumptions and notations
  • 4. Gauge function
  • 5. The Brownian motion and the Green function
  • 6. Time change of the Brownian motion
  • 7. Scaling of the Green function
  • 8. Resolvents
  • 9. Poincaré inequality
  • 10. Heat kernel, existence and continuity
  • 11. Measures having weak exponential decay
  • 12. Protodistance and diagonal lower estimateof heat kernel
  • 13. Proof of Theorem 1.1
  • 14. Random measures having weak exponential decay
  • 15. Volume doubling measure and sub-Gaussian heat kernel estimate
  • 16. Examples
  • 17. Construction of metrics from gauge function
  • 18. Metrics and quasimetrics
  • 19. Protodistance and the volume doubling property
  • 20. Upper estimate of $p_{\mu }(t, x, y)$
  • 21. Lower estimate of $p_{\mu }(t, x, y)$
  • 22. Non existence of super-Gaussian heat kernel behavior

Abstract

In this paper, time changes of the Brownian motions on generalized Sierpinski carpets including $n$-dimensional cube $[0, 1]^n$ are studied. Intuitively time change corresponds to alteration to density of the medium where the heat flows. In case of the Brownian motion on $[0, 1]^n$, density of the medium is homogeneous and represented by the Lebesgue measure. Our study includes densities which are singular to the homogeneous one. We establish a rich class of measures called measures having weak exponential decay. This class contains measures which are singular to the homogeneous one such as Liouville measures on $[0, 1]^2$ and self-similar measures. We are going to show the existence of time changed process and associated jointly continuous heat kernel for this class of measures. Furthermore, we obtain diagonal lower and upper estimates of the heat kernel as time tends to $0$. In particular, to express the principal part of the lower diagonal heat kernel estimate, we introduce “protodistance”associated with the density as a substitute of ordinary metric. If the density has the volume doubling property with respect to the Euclidean metric, the protodistance is shown to produce metrics under which upper off-diagonal sub-Gaussian heat kernel estimate and lower near diagonal heat kernel estimate will be shown.

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