Uniform approximation problems of expanding Markov maps

Abstract: Let $ T:[0,1]\to[0,1] $ be an expanding Markov map with a finite partition. Let $ \mu_\phi $ be the invariant Gibbs measure associated with a H\"older continuous potential $ \phi $. In this paper, we investigate the size of the uniform approximation set [\mathcal U^\kappa(x):={y\in[0,1]:\forall N\gg1,~\exists n\le N, \text{ such that }|T^nx-y|<N^{-\kappa}},] where $ \kappa>0 $ and $ x\in[0,1] $. The critical value of $ \kappa $ such that $ \textrm{dim}{\textrm H}\mathcal U^\kappa(x)=1 $ for $ \mu\phi $-a.e.$ \, x $ is proven to be $ 1/\alpha_{\max} $, where $ \alpha_{\max}=-\int \phi\,d\mu_{\max}/\int\log|T'|\,d\mu_{\max} $ and $ \mu_{\max} $ is the Gibbs measure associated with the potential $ -\log|T'| $. Moreover, when $ \kappa>1/\alpha_{\max} $, we show that for $ \mu_\phi $-a.e.$ \, x $, the Hausdorff dimension of $ \mathcal U^\kappa(x) $ agrees with the multifractal spectrum of $ \mu_\phi $.