On diffusions with discontinuous scales

Abstract

It is well known that a regular diffusion on an interval $I$ without killing inside is uniquely determined by a canonical scale function $s$ and a canonical speed measure $m$. Note that $s$ is a strictly increasing and continuous function and $m$ is a fully supported Radon measure on $I$. In this paper we will associate a general triple $(I,s,m)$, where $s$ is only assumed to be increasing and $m$ is not necessarily fully supported, to certain Markov processes by way of Dirichlet forms. Using two transformations, called scale completion and darning respectively, to rebuild the topology of $I$, we will successfully regularize the triple $(I,s,m)$ and obtain a regular Dirichlet form associated with it. The corresponding Markov process is called the regularized Markov process associated with $(I,s,m)$. In fact, it is the unique Markov process up to homeomorphism that can be associated with $(I,s,m)$ in the context of regular representations of Dirichlet forms. As a byproduct of regularized Markov process, a continuous simple Markov process, which does not satisfy the strong Markov property, will be also raised to be associated to $(I,s,m)$ without operating regularizing program. Furthermore, we will show that the regularized Markov process is identified with a skip-free Hunt process in one dimension as well as a quasidiffusion without killing inside. Note that the skip-free Hunt process generalizes the concept of regular diffusion and admits a scale function and a speed measure in an analogous manner.