The short-time limit of the Dirichlet partition function and the image   method
  In this paper we rigorously derive the $t\rightarrow 0^+$ asymptotics of the free partition function $Z_{\Omega}(t)$ for a diffusion process on tessellations of the d-dimensional Euclidean space $\mathbb{E}^d, \, d=1,2,3$ with an absorbing boundary. Utilising the path integral approach and the method of images for domains which are compatible with finite reflection subgroups of the orthogonal group $\mathbb{O}_d$, we solve this problem following a group theoretic method which was lacking from the literature. 
Agapitos N. Hatzinikitas and Nikolaos Lymouris
math-ph math.MP