Preference for evolving dark energy in light of the galaxy bispectrum

Abstract

We analyse pre-DESI clustering data using a dark energy equation of state $w(z)$ parametrised by $(w_0, w_a)$, finding a $2.8-3.9\sigma$ preference for evolving dark energy over the cosmological constant $\Lambda$ when combined with cosmic microwave background data from \textit{Planck} and supernova data from Pantheon+, Union3, or DESY5. Our constraints, consistent with DESI Y1 results, are derived from the power spectrum and bispectrum of SDSS/BOSS galaxies using the Effective Field Theory of Large Scale Structure (EFTofLSS) at one loop. The evidence, estimated as the Gaussian-equivalent significance from the $\Delta \chi^2$-statistics to $(w_0, w_a) = (-1, 0)$ for two degrees of freedom, remains robust across analysis variations but disappears without the one-loop bispectrum. When combining DESI baryon acoustic oscillations with BOSS full-shape data, while marginalising over the sound horizon in the latter to partially mitigate potential correlations, the significance increases to $3.7-4.4\sigma$, depending on the supernova dataset. Using instead a data-driven reconstruction of $w(z)$, we show that deviations from $\Lambda$ can be observed at multiple redshifts, though at a low level of significance: only when imposing the specific parametrisation implied by $(w_0, w_a)$ the above evidence emerges. In addition, our findings are interpreted within the Effective Field Theory of Dark Energy (EFTofDE), from which we explicitly track the non-standard time evolution in EFTofLSS predictions. For perturbatively stable theories in the $w < -1$ regime, the preference for $w_0w_a$CDM persists notably in the clustering limit $(c_s^2 \rightarrow 0)$ when higher-derivative corrections are present.