Intersection graphs of ideals of rings

In this paper we consider the intersection graph G(R) of nontrivial left ideals of a ring R. We characterize the rings R for which the graph G(R) is disconnected and obtain several necessary and sufficient conditions on a ring R such that G(R) is complete. For a commutative ring R with identity we show that G(R) is complete if and only if G(R[x]) is also so. In particular, we determine the values of n for which G(Zn) is connected, complete, bipartite, planar or has a cycle. Next we characterize finite graphs which are the intersection graphs of Zn and determine the set of all non-isomorphic graphs of Zn for a given number of vertices. We also determine the values of n for which the graph of Zn is Eulerian and Hamiltonian.