English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The presence of a significant amount of gravitational radiation in the earlyUniverse affects the total energy density and hence the expansion rate in theearly epoch. In this work, we develop a physical model to connect the parameterof relativistic degree of freedom $N_\mathrm{eff}$ with the amplitude and shapeof primordial tensor power spectrum, and use the CMB temperature andpolarization data from {\it Planck} and BICEP2/KECK Array, and the primordialdeuterium measurement from damped Lyman-$\alpha$ (DLA) systems to constrainthis model. We find that with this extra relation $\Delta N_{\rm eff}(r,n_{\rmt})$, the tensor-to-scalar ratio $r$ is constrained to be $r<0.07$ ($3\sigma$C.L.) and the tilt of tensor power spectrum is $n_\mathrm{t}=-0.01\pm 0.31$($1\sigma$ C.L.) for {\it Planck}+BICEP2+KECK+[D/H] data. This achieves a muchtighter constraint on the tensor spectrum and provides a stringent test forcosmic inflation models. In addition, the current constraint on $N_{\rmeff}=3.122 \pm 0.171$ excludes the possibility of fourth neutrino species atmore than $5\sigma$ C.L.

How much primordial tensor mode is allowed?