The trace formula for a point scatterer on a hyperbolic surface with one   cusp
  We prove an exact trace formula for the Laplacian with a delta potential - also known as a point scatterer - on a non-compact hyperbolic surface of finite volume with one cusp. Our formula is an analogue of the Selberg trace formula. We express the difference of perturbed and unperturbed trace as a smooth term plus a sum over combinations of diffractive orbits. 
Henrik Ueberschaer
math-ph math.MP