How much primordial tensor mode is allowed?
Abstract
The presence of a significant amount of gravitational radiation in the early Universe affects the total energy density and hence the expansion rate in the early epoch. In this work, we develop a physical model to connect the number of relativistic degrees of freedom N_{eff} 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 Lymanα systems to constrain this model. We find that with the extra relation ∆ N_{eff}(r ,n_{t}), the tensortoscalar ratio r is constrained to be r <0.07 (3 σ C.L.) and the tilt of the tensor power spectrum is n_{t}=0.01 ±0.31 (1 σ C.L.) for P l a n c k +BICEP 2 +KECK +[D /H ] data. This achieves a much tighter constraint on the tensor spectrum and provides a stringent test for cosmic inflation models. In addition, the current constraint on N_{eff}=3.122 ±0.171 excludes the possibility of a fourth neutrino species at more than 5 σ C.L.
 Publication:

Physical Review D
 Pub Date:
 March 2020
 DOI:
 10.1103/PhysRevD.101.063536
 arXiv:
 arXiv:1912.00995
 Bibcode:
 2020PhRvD.101f3536A
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 12 pages, 7 figures