Dirac operators and the calculation of the Connes metric on arbitrary (infinite) graphs

As an outgrowth of our investigation of non-regular spaces within the context of quantum gravity and non-commutative geometry, we develop a graph Hilbert space framework on arbitrary (infinite) graphs and use it to study spectral properties of graph Laplacians and graph Dirac operators. We define a spectral triplet sharing most of the properties of what Connes calls a spectral triple. With the help of this scheme we derive an explicit expression for the Connes-distance function on general directed or undirected graphs. We derive a series of a priori estimates and calculate it for a variety of examples of graphs. As a possibly interesting side, we show that the natural setting for approaching such problems may be the framework of (non)linear programming or optimization. We compare our results (arrived at within our particular framework) with those of other authors and show that the seeming differences depend on the use of different graph geometries and/or Dirac operators. (author)