Peculiarities for scalar fields in GR domain walls

In the present letter, the solutions of the Klein Gordon equation in the space time of an infinite domain wall is studied. It is shown that the horizon is an special region, where initial conditions (scattering conditions) at asymptotic past for the field can not be defined. This is in harmony with the fact that this region can not be crossed, a possibility that was suggested in \cite{lanosa}. If these results are correct, then it makes no sense to impose boundary conditions at this location.