Footprint of Two-Form Field: Statistical Anisotropy in Primordial
  Gravitational Waves
  We study the observational signatures of two-form field in the inflationary
cosmology. In our setup a two-form field is kinetically coupled to a spectator
scalar field and generates sizable gravitational waves and smaller curvature
perturbation. We find that the sourced gravitational waves have a distinct
signature: they are always statistically anisotropic and their spherical
moments are non-zero for hexadecapole and tetrahexacontapole, while the
quadrupole moment vanishes. Since their amplitude can reach
$\mathcal{O}(10^{-3})$ in the tensor-to-scalar ratio, we expect this novel
prediction will be tested in the next generation of the CMB experiments.
