Measure-valued solutions of scalar hyperbolic conservation laws, Part 1: Existence and time evolution of singular parts

We prove existence for a class of signed Radon measure -valued entropy solutions of the Cauchy problem for a first order scalar hyperbolic conservation law in one space dimension. The initial data of the problem is a finite superposition of Dirac masses, whereas the flux is Lipschitz continuous. Existence is proven by a constructive procedure which makes use of a suitable family of approximating problems. Relevant qualitative properties of such constructed solutions are pointed out.