Finite dimensionality of Besov spaces and potential-theoretic decomposition of metric spaces

In the context of a metric measure space (X, d, mu), we explore the potential-theoretic implications of having a finite-dimensional Besov space. We prove that if the dimension of the Besov space B-p,p(theta)(X) is k> 1, then X can be decomposed into k number of irreducible components (Theorem 1.1). Note that 9 may be bigger than 1, as our framework includes fractals. We also provide sufficient conditions under which the dimension of the Besov space is 1. We introduce critical exponents theta(p)(X) and theta(& lowast;)(p)(X) for the Besov spaces. As examples illustrating Theorem 1.1, we compute these critical exponents for spaces X formed by glueing copies of n-dimensional cubes, the Sierpi & nacute;ski gaskets, and of the Sierpi & nacute;ski carpet.