Suppose $π:\mathbb R^d \to \mathbb R^d, \sigma:\mathbb R^d \to \mathbb R^{d\times d}$ are measurable functions and satisfy \begin{equation*} 2\langle π₯βπ¦,π(π₯)βπ(π¦)\rangle +\|\sigma(π₯)β\sigma(π¦)\|^2 \le πΎ|π₯βπ¦| \rho(|π₯βπ¦|),\ \ \ \ {(1)}\end{equation*} for all $π₯,π¦ \in \mathbb R^d$, where $\rho:[0, \infty)β[0,\infty)$ is some appropriate function. In addition, assume that the SDE $$ππ(π‘)=π(π(π‘))ππ‘+ \sigma(π(π‘))ππ(π‘)$$ is well-posed in the strong sense.
We now consider the coupled process $$\begin{aligned} & ππ(π‘)=π(π(π‘))ππ‘+\sigma(π(π‘))ππ(π‘), \\ & ππ(π‘)=π(π(π‘))ππ‘+\sigma(π(π‘))ππ(π‘),\end{aligned}$$ where $π$ is a $π$-dimensional standard Brownian motion. Is it true that for all $t\geq 0$ the following estimate is true? \begin{equation*} π|π(π‘)βπ(π‘)|β€\rho(|π(π‘)βπ(π‘)|)ππ‘+\left\langle \frac{π(π‘)βπ(π‘)}{|π(π‘)βπ(π‘)|},(\sigma(π(π‘))β\sigma(π(π‘)))ππ(π‘)\right\rangle.\ {(2)}\end{equation*}
Using Ito's formula, we have $$ π|π(π‘)βπ(π‘)|^2=(2\langle π(π‘)βπ(π‘),π(π(π‘))βπ(π(π‘))\rangle + \|\sigma(π(π‘))β\sigma(π(π‘))\|^2)ππ‘+2\langle π(π‘)βπ(π‘),(\sigma(π(π‘))β\sigma(π(π‘)))ππ(π‘)\rangle.$$ Using (1), and applying Ito's formula to the process $|π(π‘)βπ(π‘)|^2$ using the function $π(π)=π^{1/2}, π\ge 0,$ we can formally derive (2). But there is a problem, as $π$ is not differentiable at 0. But I don't know how to rigorously prove or disprove (2).
Thanks a lot for your help. (I posted this question in Stack Exchange, but no answer yet).