A Note on One-dimensional Stochastic Differential Equations with Generalized Drift

TL;DR

This paper studies one-dimensional stochastic differential equations with generalized drift involving local time, extending analysis to cases where the drift measure exceeds traditional bounds, and characterizes solution behaviors in these regimes.

Contribution

It provides a comprehensive analysis of SDEs with generalized drift when the measure exceeds standard bounds, expanding understanding beyond classical conditions.

Findings

Characterizes solutions for /2  and  bounds on the drift measure.

Identifies conditions for existence and uniqueness in extended drift regimes.

Describes solution features when the drift measure surpasses classical thresholds.

Abstract

We consider one-dimensional stochastic differential equations with generalized drift which involve the local time $L^X$ of the solution process: X_t = X_0 + \int_0^t b(X_s) dB_s + \int_\mathbb{R} L^X(t,y) \nu(dy), where b is a measurable real function, $B$ is a Wiener process and $\nu$ denotes a set function which is defined on the bounded Borel sets of the real line $\mathbb{R}$ such that it is a finite signed measure on $\mathscr{B}([-N,N])$ for every $N \in \mathbb{N}$. This kind of equation is, in dependence of using the right, the left or the symmetric local time, usually studied under the atom condition $\nu({x}) < 1/2$, $\nu({x}) > -1/2$ and $|\nu({x})| < 1$, respectively. This condition allows to reduce an equation with generalized drift to an equation without drift and to derive conditions on existence and uniqueness of solutions from results for equations without drift. The main aim of the present note is to treat the cases $\nu({x}) \geq 1/2$, $\nu({x}) \leq -1/2$ and $|\nu({x})| \geq 1$, respectively, for some $x \in \mathbb{R}$, and we give a complete description of the features of equations with generalized drift and their solutions in these cases.