Non-Parallel Electric and Magnetic Fields in a Gravitational Background,   Stationary Gravitational Waves and Gravitons
  The existence of an electromagnetic field with parallel electric and magnetic field components in the presence of a gravitational field is considered. A non-parallel solution is shown to exist. Next, we analyse the possibility of finding stationary gravitational waves in nature. Finally, we construct a D=4 effective quantum gravity model. Tree-level unitarity is verified. 
Carlos Pinheiro (UFES, Brazil), J.A.Helayel-Neto (CBPF & UCP, Brazil),   Gilmar S. Dias (UFES, Brazil), F.C. Khanna (UofA, C...