Probing dark energy evolution with Quaia quasars through the integrated Sachs-Wolfe effect

The Integrated Sachs--Wolfe effect probes the late-time evolution of gravitational potentials and provides a complementary test of the nature of dark energy. The new analysis still awaits peer review, but it already lays out the central claim clearly.

It is relevant because cosmology operates at the edge of what current instruments can measure, where systematic errors and model assumptions are never trivial. Small discrepancies between independent measurements have historically pointed toward missing physics rather than simple calibration errors, and the ongoing tension in the Hubble constant is a live example of how a persistent disagreement between methods can reshape the theoretical landscape. Each new dataset that approaches this territory with independent systematics adds real information to a problem that has resisted easy resolution for more than a decade. The Integrated Sachs--Wolfe (ISW) effect probes the late-time evolution of gravitational potentials and provides a complementary test of the nature of dark energy. We investigate whether the redshift evolution of the ISW effect can provide new constraints on the time evolution of dark energy.

We consider theoretical predictions for the standard $Λ$CDM cosmology and alternative $w_0w_a$CDM models favoured by recent DESI BAO and DES Y6 constraints. We perform a tomographic cross-correlation analysis of the {\it Quaia} quasar catalogue and \textit{Planck} CMB temperature maps to measure the ISW signal over a broad redshift.

We assess the robustness of the inferred ISW amplitude against variations in sky coverage, multipole range, and tomographic binning. We detect the ISW effect at a significance of $2.8 \, σ$, corresponding to an amplitude of $A_{\rm ISW}\simeq1.69\pm0.61$ relative to the \textit{Planck} $Λ$CDM prediction.

The inferred signal remains stable against various analysis choices, including various CMB maps (SMICA, NILC, SEVEM), different choices of $\ell_{\rm max}$ and the number of. The measured ISW amplitude is moderately stronger than predicted by the fiducial $Λ$CDM cosmology, and the alternative $w_0w_a$CDM models do not account for this discrepancy.

The relevance goes beyond one dataset because even small shifts in measured parameters can matter when the field is testing the limits of the standard cosmological model. The Lambda-CDM framework describes the observable universe with remarkable economy, but its success rests on two components, dark matter and dark energy, whose physical nature remains entirely unknown. Any credible measurement that tightens or loosens the constraints on those components moves the entire theoretical enterprise forward, regardless of whether the immediate result looks dramatic on its own terms.

Future tomographic ISW measurements with improved quasar catalogues from {\it Gaia} and forthcoming wide-area galaxy surveys such as {\it Euclid} and DESI will help clarify the. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy.

Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to see whether the effect survives when independent surveys, different calibration strategies and tighter control of systematic uncertainties enter the picture. Programmes such as Euclid, DESI and the Rubin Observatory will deliver datasets over the next several years that cover the same parameter space with largely independent methods. If the current signal persists through those tests, its theoretical implications will become impossible to set aside. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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