[1] Univ Siegen, Ctr Particle Phys Siegen, Theoret Phys 1, D-57068 Siegen, Germany
[2] Maastricht Univ, Gravitat Waves & Fundamental Phys GWFP, Duboisdomein 30, NL-6229 GT Maastricht, Netherlands
[3] Nikhef, Sci Pk 105, NL-1098 XG Amsterdam, Netherlands