A new class of Volterra-type integral equations from relativistic quantum physics

Abstract

We study a new kind of linear integral equations for a relativistic quantum-mechanical two-particle wave function ψ(x1, x2), where x1, x2 are spacetime points. In the case of retarded interaction, these integral equations are of Volterra-type in the in the time variables, i.e., they involve a time integration from 0 to ti =x0i i = 1,2. They are interesting not only in view of their applications in physics, but also because of the following mathematical features: (a) time and space variables are more interrelated than in normal time-dependent problems, (b) the integral kernels are singular, and the structure of these singularities is non-trivial, (c) they feature time delay. We formulate a number of examples of such equations for scalar wave functions and prove existence and uniqueness of solutions for them. We also point out open mathematical problems.