Scattering Theory for Klein-Gordon Equations with Non-Positive Energy

Abstract

We study the scattering theory for charged Klein-Gordon equations: describing a Klein-Gordon field minimally coupled to an external electromagnetic field described by the electric potential v(x) and magnetic potential, The flow of the Klein-Gordon equation preserves the energy, We consider the situation when the energy is not positive. In this case the flow cannot be written as a unitary group on a Hilbert space, and the Klein-Gordon equation may have complex eigenfrequencies. Using the theory of definitizable operators on Krein spaces and time-dependent methods, we prove the existence and completeness of wave operators, both in the short- and long-range cases. The range of the wave operators are characterized in terms of the spectral theory of the generator, as in the usual Hilbert space case. © 2011 Springer Basel AG.