http://arxiv.org/abs/1710.09818
The impact of the existence of gravitons with non-vanishing masses on the B modes of the Cosmic Microwave Background (CMB) is investigated. We also focus on putative modifications to the speed of the gravitational waves. We find that a change of the graviton speed shifts the acoustic peaks of the CMB and then could be easily constrained. For the case of massive gravity, we show analytically how the B modes are sourced in a manner differing from the massless case leading to a plateau at low $l$ in the CMB spectrum. We also study the case when there are more than one graviton, and when pressure instabilities are present. The latter would occur in doubly coupled bigravity in the radiation era. We show that by coupling two gravitons to matter there is a wider range of effects including a space of parameters where there is no detectable difference with massless gravity. When the tachyonic instability in the radiation era is present, the amplitude of the B-modes increases by several orders of magnitude and the tail of the power spectrum changes its slope. This would exclude these models unless the tensor to scalar ratio in the inflationary era is extremely small.
P. Brax, S. Cespedes and A. Davis
Fri, 27 Oct 17
17/60
Comments: N/A
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