Probing neutrino interactions and dark radiation with gravitational waves

Understand

After their generation, cosmological backgrounds of gravitational waves propagate nearly freely but for the expansion of the Universe and the anisotropic stress of free-streaming particles.

• Primordial signals -- both that from inflation and the infrared spectrum associated to subhorizon production mechanisms -- would carry clean information about the cosmological history of these effects.
• We study the modulation of the standard damping of gravitational waves by free-streaming radiation due to the decoupling (or recoupling) of interactions.
• We focus on nonstandard neutrino interactions in effect after the decoupling of weak interactions as well as more general scenarios in the early Universe involving other light relics.