Primordial gravitational waves from conformal gravity
  We investigate the evolution of cosmological perturbations generated during de Sitter inflation in the conformal gravity. Primordial gravitational waves are composed of vector and tensor modes. We obtain the constant vector and tensor power spectra which seems to be correct because the conformal gravity is invariant under conformal transformation like the Maxwell kinetic term. 
Yun Soo Myung, Taeyoon Moon
gr-qc hep-th