http://arxiv.org/abs/2303.17985
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.
N. Jokela, K. Kajantie, M. Laine, et. al.
Mon, 3 Apr 23
34/53
Comments: 8 pages