Evolving and interacting dark energy: photometric and spectroscopic synergy with DES Y3 and DESI DR2

TL;DR

This work tests Dark Scattering (DS), a momentum-exchange interacting dark energy model, against a CPL parametrisation of the dark energy equation of state using a joint data set from DES Y3 3×2pt, DESI DR2 BAO, DES Y5 SNe, and Planck CMB. The nonlinear DS boost is modeled with halo-model reaction and a neural-network emulator to enable fast predictions, while CPL is used as a comparative baseline. The analysis finds A_ds consistent with zero across data combinations and shows CPL generally provides a better fit; including DES photometric data substantially improves the constraints on (w0, wa), particularly for DS, by up to ~50%. No evidence for an S8 tension is detected in either model, and these results set the most stringent pre-Euclid constraints on DS by combining photometric and spectroscopic information. The findings highlight the value of photometric-spectroscopic synergy for constraining late-time cosmology and set the stage for future tests with Euclid and Rubin.

Abstract

We investigate the Dark Scattering (DS) interacting dark energy scenario, characterised by pure momentum exchange between dark matter and dark energy, allowing for a time-dependent equation-of-state described by the Chevallier-Polarski-Linder (CPL) parametrisation. This class of models is weakly constrained by CMB observations and can exhibit distinctive late-time suppression of structure growth. We derive constraints on cosmological, DS, and CPL parameters using three two-point correlation functions from the Dark Energy Survey Year 3 data, combined with baryon acoustic oscillation measurements from DESI, Type Ia supernovae from DES Year 5, and CMB data from Planck. We find the dark-sector interaction parameter $A_\mathrm{ds}$ to be consistent with zero for all data combinations, and that CPL provides a statistically preferred fit over DS for the selected probes. From the full data combination we obtain $w_0=-0.76\pm0.06, \, w_a=-0.77^{+0.23}_{-0.20}$ for CPL, and $w_0=-0.79^{+0.05}_{-0.06}, \, w_a=-0.56^{+0.24}_{-0.15}, \, (A_\mathrm{ds}=9.8^{+2.8}_{-9.5}\,\mathrm{bn/GeV} )$ for DS. The inclusion of DES photometric information improves the Figure-of-Merit on $(w_0,w_a)$ by $\sim$20% for CPL and $\sim$50% for DS relative to DESI+SN+CMB alone. We find no evidence for an $S_8$ discrepancy in either model. These results provide the most stringent pre-Euclid constraints on DS from a combined photometric and spectroscopic analysis.

Figures (7)

• Figure 1: Linear growth factor in DS with respect to $\Lambda$CDM today, overlayed with https://data.desi.lbl.gov/public/papers/y3/bao-cosmo-params/README.html DESI results for evolving dark energy without interaction (specific combinations of cosmological probes are shown in the legend). The reddish region on the heatmap denotes enhancement of structure growth with respect to $\Lambda$CDM, while the blueish region denotes suppression. Grey dashed lines mark the $\Lambda$CDM-limit for the dark energy equation-of-state. Dark red dashed line denotes the suppression/enhancement transition, i.e. $D_\mathrm{DS} \approx D_{\Lambda \mathrm{CDM}}$, for different values of the interaction strength $\xi$ (in units of [bn/GeV]).
• Figure 2: Quantiles of the relative accuracy of our DS emulator on $6 \cdot 10^4$ testing samples. The dashed grey line denotes the 1% accuracy.
• Figure 3: Dark energy results for different data selections, specified in the legend of the lower panels. CPL constraints are shown in dark red, DS constraints are shown in blue. All contours shown contain 68% and 95% of the posterior probability. Dashed yellow regions denote priors in DS: $w_0+w_a<-1/2$ for the existence of a growing solution of the linearised growth equation and $0<\xi<150$ [bn/GeV].
• Figure 4: CPL: constraints without (in blue) and with (in dark red) photometric information from DES. Grey dashed lines denote $\Lambda$CDM limit in equation-of-state parameters. Grey stripe denotes constraints from Planck 2018 without lensing for $\Lambda$CDM planck2018cosmo.
• Figure 5: Same as \ref{['fig:cpl+spectro+photo']} for DS. Dashed yellow regions denote prior constraints same as in \ref{['fig:w0waAds']}.