Damping of Primordial Gravitational Waves from Generalized Sources

Abstract

It has been shown that a cosmological background with an anisotropic stress tensor, appropriate for a free streaming thermal neutrino background, can damp primordial gravitational waves after they enter the horizon, and can thus affect the CMB B-mode polarization signature due to such tensor modes. Here we generalize this result, and examine the sensitivity of this effect to non-zero neutrino masses, extra neutrino species, and also a possible relativistic background of axions from axion strings. In particular, additional neutrinos with cosmologically interesting neutrino masses at the O(1) eV level will noticeably reduce damping compared to massless neutrinos for gravitational wave modes with $k{\tau }_0\approx 100-200$, where ${\tau }_0\approx 2/H_0$ and $H_0$ is the present Hubble parameter, while an axion background would produce a phase-dependent damping distinct from that produced by neutrinos.

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Cited by in corpus (14)

• Primordial gravitational waves, precisely: The role of thermodynamics in the Standard Model
• Primordial Gravitational Waves in Nonstandard Cosmologies
• Damping of gravitational waves by matter
• Friction in Gravitational Waves: a test for early-time modified gravity
• Towards a reliable calculation of relic radiation from primordial gravitational waves
• Impact of high-scale Seesaw and Leptogenesis on inflationary tensor perturbations as detectable gravitational waves
• Microphysical manifestations of viscosity and consequences for anisotropies in the very early universe
• Probing neutrino interactions and dark radiation with gravitational waves
• Impact of the free-streaming neutrinos to the second order induced gravitational waves
• Relativistic viscous effects on the primordial gravitational waves spectrum
• Damping of gravitational waves in f(R) gravity
• Primordial gravitational waves from spontaneous Lorentz symmetry breaking
• Interaction of exact gravitational waves with matter
• Primordial observables of explicit diffeomorphism violation in gravity