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Inflationary gravitational wave background as a tail effect (2303.17985v2)
Published 31 Mar 2023 in gr-qc, astro-ph.CO, and hep-ph
Abstract: The free propagator of a massless mode in an expanding universe can be written as a sum of two terms, a lightcone and a tail part. The latter describes a subluminal (time-like) signal. We show that the inflationary gravitational wave background, influencing cosmic microwave background polarization, and routinely used for constraining inflationary models through the so-called $r$ ratio, originates exclusively from the tail part.
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