We consider the inflationary universe with a spectator scalar field coupled to a U(1) gauge field and calculate curvature perturbation and gravitational waves (GWs). We find that the sourced GWs can be larger than the one from vacuum fluctuation and they are statistically anisotropic as well as linearly polarized. The GW power spectrum acquires higher multipole moments with respect to the angle θ between a wave number k and a background vector field as h∝ (1-cos2θ+cos4θ-cos6θ) irrespective of the model parameters.
- physics of the early universe
ASJC Scopus subject areas
- Astronomy and Astrophysics