Averaging principle for SDEs with singular drifts driven by $\alpha$-stable processes

In this paper, we investigate the convergence rate of the averaging principle for stochastic differential equations (SDEs) with $\beta$-H\"older drift driven by $\alpha$-stable processes. More specifically, we first derive the Schauder estimate for nonlocal partial differential equations (PDEs) associated with the aforementioned SDEs, within the framework of Besov-H\"older spaces. Then we consider the case where $(\alpha,\beta)\in(0,2)\times(1-\tfrac{\alpha}{2},1)$. Using the Schauder estimate, we establish the strong convergence rate for the averaging principle. In particular, under suitable conditions we obtain the optimal rate of strong convergence when $(\alpha,\beta)\in(\tfrac{2}{3},1]\times(2-\tfrac{3\alpha}{2},1)\cup(1,2)\times(\tfrac{\alpha}{2},1)$. Furthermore, when $(\alpha,\beta)\in(0,1]\times(1-\alpha,1-\tfrac{\alpha}{2}]\cup(1,2)\times(\tfrac{1-\alpha}{2},1-\tfrac{\alpha}{2}]$, we show the convergence of the martingale solutions of original systems to that of the averaged equation. When $\alpha\in(1,2)$, the drift can be a distribution.