Collision of electromagnetic shock waves coupled with axion waves: an example

We present an exact solution that describes the collision of electromagnetic shock waves coupled with axion plane waves. The axion has a rather special coupling to the cross-polarization term of the metric. The initial data on the null surfaces are well defined and collision results in a singularity-free interaction region. Our solution is a generalization of the Bell–Szekeres solution in the presence of an axion field.