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arXiv · 2502.17395

Back-Reaction of Super-Hubble Fluctuations, Late Time Tracking and Recent Observational Results

Marco Antonio Cardoso Alvarez·Leila Graef·Robert Brandenberger
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Abstract

Previous studies suggested that the back-reaction of super-Hubble cosmological fluctuations could lead to a dynamical relaxation of the cosmological constant. Moreover, this mechanism appears to be self-regulatory, potentially leading to an oscillatory behavior in the effective dark energy. Such an effect would occur in any cosmological model with super-Hubble matter fluctuations, including the standard $\Lambda\text{CDM}$ model. The recent DESI data, which indicate that dark energy may be dynamical, has renewed interest in exploring scenarios leading to such oscillatory behavior. In this work we propose a parametrization to account for the impact of super-Hubble fluctuations on the background energy density of the Universe. We model the total effective cosmological constant as the sum of a constant piece and an oscillating contribution. We perform a preliminary comparison of the background dynamics of this model with the recent radial BAO data from DESI. We also discuss the status of the $H_0$ tension problem in this model.

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Marco Antonio Cardoso Alvarez, Leila Graef, Robert Brandenberger. 2025-02-24. Back-Reaction of Super-Hubble Fluctuations, Late Time Tracking and Recent Observational Results. https://arxiv.org/abs/2502.17395

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