Temperature fluctuations in an inhomogeneous diffusive fluid

Abstract

We discuss metric perturbations of the relativistic diffusion equation around the homogeneous Juttner equilibrium of massless particles in a homogeneous expanding universe. The metric perturbation describes matter distribution and the gravitational wave background in an inhomogeneous universe. We show that the lowest order perturbation can be treated as a variation of temperature. We derive a formula expressing temperature fluctuations in terms of the diffusion and tensor power spectrum. We discuss the multipole expansion of the fluctuations in the presence of diffusion.

14 pages,minor corrections

References in corpus (4)

• Extended Limber Approximation
• Enhanced polarization of CMB from thermal gravitational waves
• Relativistic diffusion
• Non-linear relativistic diffusions