Towards primordial gravitational waves and $n_s=1$ in light of BICEP/Keck, DESI BAO and Hubble tension

• DOI: 10.48550/arxiv.2409.17879
• Publication Date: 2024-01-01
• Authors: Wang, Hao; Ye, Gen; Jiang, Jun-Qian; Piao, Yun-Song
• Keywords: Cosmology and Nongalactic Astrophysics (astro-ph.CO); FOS: Physical sciences; General Relativity and Quantum Cosmology (gr-qc); General Relativity and Quantum Cosmology; Astrophysics - Cosmology and Nongalactic Astrophysics

Recent observational data seem to show a $\gtrsim 3σ$ evidence for an evolving dark energy (DE) against the cosmological constant, so the standard $Λ$CDM model. In this paper, we perform the search for the primordial gravitational waves with the potential pre-recombination solutions to the Hubble tension, using recent DESI baryon acoustic oscillation measurements combined with BICEP/Keck cosmic microwave background (CMB) B-mode polarization, Planck CMB and Pantheon supernova data, which reveal that the low bound of the tensor-to-scalar ratio $r$ is $> 1.5σ$ non-zero with the bestfit $r_{0.05}\sim 0.01$ and the scalar spectral index $n_s= 1$ (both $|r_{0.05}-0.01|$ and $|n_s-1|\sim {\cal O} (0.001)$). In particular, we observe the unnoticed impact of CMB B-mode polarization data for constraining the nature of DE, which together with early dark energy solutions to the Hubble tension is calling for the return of post-recombination $Λ$CDM.<br/>15 pages, 3 figures<br/>