New constraints on cosmological gravitational waves from CMB and BAO in light of dynamical dark energy

Abstract

In this work, we derive upper limits on the physical energy-density fraction today of cosmological gravitational waves, denoted by ${\Omega }_{\mathrm{gw}}{h}^2$, via analyzing \emph{Planck} \& ACT \& SPT CMB and DESI BAO data combination. In the standard cosmological model, we establish 95\% CL upper limits of ${\Omega }_{\mathrm{gw}}{h}^2<1.0\times 10^{-6}$ for adiabatic initial conditions and ${\Omega }_{\mathrm{gw}}{h}^2<2.7\times 10^{-7}$ for homogeneous initial conditions, assuming a uniform prior for ${\Omega }_{\mathrm{gw}}{h}^2$. In light of dynamical dark energy, we get ${\Omega }_{\mathrm{gw}}{h}^2<7.2\times 10^{-7}$ (adiabatic) and ${\Omega }_{\mathrm{gw}}{h}^2<2.4\times 10^{-7}$ (homogeneous). In contrast, if a log-uniform prior was assumed for ${\Omega }_{\mathrm{gw}}{h}^2$, these constraints can become tighter by a factor of $\sim 4$, suggesting the results to be prior-sensitive. Furthermore, we project the sensitivity achievable with LiteBIRD \& CMB Stage-IV measurements of CMB and CSST observations of BAO, forecasting 68\% CL uncertainties of $\sigma =2.5\times 10^{-7}$ (adiabatic) and $\sigma =1.0\times 10^{-7}$ (homogeneous) for ${\Omega }_{\mathrm{gw}}{h}^2$. The constraints we obtained in this work provide critical benchmarks for exploring the cosmological origins of gravitational waves within the frequency band $f\gtrsim 10^{-15}$\,Hz and potentially enable joint analysis with direct gravitational-wave detection sensitive to this regime.

12 pages, one column, 4 figures, 3 tables, to appear in the Chinese Physics C

Cited by in corpus (1)

• Testing signatures of phantom crossing through full-shape galaxy clustering analysis