Probing pre-inflationary anisotropy with directional variations in the   gravitational wave background
  We perform a detailed analysis on a primordial gravitational-wave background amplified during a Kasner-like pre-inflationary phase allowing for general triaxial anisotropies. It is found that the predicted angular distribution map of gravitational-wave intensity on large scales exhibits topologically distinctive patterns according to the degree of the pre-inflationary anisotropy, thereby serving as a potential probe for the pre-inflationary early universe with future all-sky observations of gravitational waves. We also derive an observational limit on the amplitude of such anisotropic gravitational waves from the B-mode polarisation of the cosmic microwave background. 
Yu Furuya, Yuki Niiyama, Yuuiti Sendouda
astro-ph.CO gr-qc hep-th