Collision of Electromagnetic Shock Waves Coupled with Axion Waves: An Example

We present an exact solution that describes 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 is 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.