  We obtain global space-time weighted-L^2 (Morawetz) and L^4 (Strichartz)
estimates for a massless chargeless scalar field propagating on a
super-extremal (overcharged) Reissner-Nordstrom background. We begin by
discussing the question of well-posedness of the Cauchy problem for scalar
fields on non-globally hyperbolic manifolds and the role played by the
Friedrichs extension, go over the construction of the function spaces involved,
show how to transform the problem to one about the wave equation on the
Minkowski space with a singular potential, and finally prove that the potential
thus obtained satisfies the various conditions needed in order for the
estimates to hold.
