What does this research mean for the field?

RCD is indistinguishable from LCDM at linear scales, with deviations in perturbations being less than 1e-6. Novelty: ClaimNovelty.CONFIRMATORY. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

This work aims to investigate the nature of linear scalar perturbations under a quasi-static cosmological background.

March 3, 2026Open Access

Linear Scalar Perturbations in the Quasi-Static Regime

Key Points

This work aims to investigate the nature of linear scalar perturbations under a quasi-static cosmological background.
Analyzed scalar perturbations in the quasi-static regime
Studied modifications of effective field theory (EFT) parameters at linear scales
Examined non-linear regime for coherence gradients
Confirmed that RCD is indistinguishable from LCDM at linear scales
Quantified modifications as occurring only in the non-linear regime
Observed that linear safety is a structural consequence of the action

Abstract

We analyze RCD linear scalar perturbations in the quasi-static regime. The homogeneous cosmological background forces all EFT modification parameters to unity: mu = eta = Sigma = 1. RCD is indistinguishable from LCDM at linear scales, with Delta (f*sigma₈) /f*sigma₈ < 1e-6. Modifications activate only in the non-linear regime where coherence gradients become non-negligible. This linear safety is a structural consequence of the action, not a tuning.

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Arturo Cerezo (Sun,) studied this question.

www.synapsesocial.com/papers/69a67eebf353c071a6f0a89b — DOI: https://doi.org/10.5281/zenodo.18827766

Linear Scalar Perturbations in the Quasi-Static Regime

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Abstract

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