The exact value of Hausdorff dimension of escaping sets of class B meromorphic functions

We consider the subclass of class $\mathcal{B}$ consisting of meromorphic functions $f:\mathbb{C}\to \widehat{\mathbb{C}}$ for which infinity is not an asymptotic value and whose all poles have orders uniformly bounded from above. This class was introduced in \cite{BwKo2012} and the Hausdorff dimension ${\rm HD}({{\mathcal I} (f)})$oftheset${{\mathcal I} (f)}$ of all points escaping to infinity under forward iteration of $f$ was estimated therein. In this paper we provide a closed formula for the exact value of ${\rm HD}({{\mathcal I} (f)})$ identifying it with the critical exponent of the natural series introduced in \cite{BwKo2012}. This exponent is very easy to calculate for many concrete functions. In particular, we construct a function from this class which is of infinite order and for which $\mathrm{H}\mathrm{D}(\mathcal{I}(f))=0$.