How much primordial tensor mode is allowed?

The presence of a significant amount of gravitational radiation inthe early Universe affects the total energy density and hence the expansion rate inthe early epoch. Inthis work, we develop a physical model to connect the number of relativistic degrees of freedom Neff with the amplitude and shape of...

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Bibliographic Details
Published in:Physical review. D 2020-03, Vol.101 (6), p.1, Article 063536
Main Authors: Aich, Moumita, Ma, Yin-Zhe, Dai, Wei-Ming, Xia, Jun-Qing
Format: Article
Language:English
Subjects:
Big Bang theory
Constraint modelling
Cosmic microwave background
Cosmic microwave background temperature
Deuterium
Expanding universe theory
Flux density
Mathematical analysis
Neutrinos
Tensors
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Summary:The presence of a significant amount of gravitational radiation inthe early Universe affects the total energy density and hence the expansion rate inthe early epoch. Inthis work, we develop a physical model to connect the number of relativistic degrees of freedom Neff with the amplitude and shape of the primordial tensor power spectrum, and use the cosmic microwave background temperature and polarization data from Planck and the BICEP2/KECK Array and the primordial deuterium measurements from damped Lyman-α systems to constrainthis model. We find that with the extra relation ΔNeff(r, nt) , the tensor-to-scalar ratio r is constrained to be r < 0.07 (3σ C.L.) and the tilt of the tensor power spectrum is nt = −0.01 ± 0.31 (1σ C.L.) for Planck + BICEP 2 + KECK + [D/H] data. This achieves a much tighter constraint onthe tensor spectrum and provides a stringent test for cosmic inflation models. In addition, the current constraint on Neff = 3.122 ± 0.171 excludes the possibility of a fourth neutrino species at more than 5σ C.L.
ISSN:2470-0010
2470-0029
DOI:10.1103/PhysRevD.101.063536