On the Anisotropy of the Gravitational Wave Background from Massless Preheating

Understand

When a light scalar field is present during inflation, its value will vary on superhorizon scales, modulating the preheating process at the end of inflation.

• Consequently, the amplitude of the gravitational wave (GW) background produced during preheating will also be modulated.
• The observed energy density of this background will therefore appear anisotropic at different angles in the sky.
• We provide a master formula for the angular power spectrum C_l of the anisotropies in the GW background from preheating, valid for any scenario where the anisotropies are due to the superhorizon modulation of a light degree of freedom.