On the connectedness of self-affine tiles

Let Tbe a self-affine tile in R-n defined by an integral expanding matrix A and a digit set D. The paper gives a necessary and sufficient condition for the connectedness of T. The condition can be checked algebraically via the characteristic polynomial of A. Through the use of this, it is shown that in R-2, for any integral expanding matrix A, there exists a digit set D such that the corresponding tile Tis connected. This answers a question of Bandt and Gelbrich. Some partial results for the higher-dimensional cases are also given.