Improved constraints on primordial gravitational waves in light of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>H</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math> tension and BICEP/Keck data
Gen Ye, Yun-Song Piao
Abstract
The ${H}_{0}$ tension that the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model is suffering from can be resolved with prerecombination early dark energy. We present the first constraint on the tensor-to-scalar ratio $r$ in corresponding ${H}_{0}$-tension-free cosmologies using the most recent BICEP/Keck cosmic microwave background (CMB) B-mode polarization data. We find, combining BICEP/Keck with Planck18 CMB and baryon acoustic oscillation data, that the models with larger Hubble-Lema\^{\i}tre-constant ${H}_{0}$ will have tighter upper bound on $r$, and resolution of the ${H}_{0}$ tension (${H}_{0}\ensuremath{\sim}73\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$) tightens the upper bound to $r<0.028(95%\text{ }\text{ }\mathrm{C}.\mathrm{L}.)$, 25% tighter than the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ constraint $r<0.036$. We clarify the origin of this tightened bound.