Marco Antonio Cardoso Alvarez

arXiv2026

A Periodically Interacting Dark Sector: Signatures and Constraints from CMB and Cosmic Expansion Data

We introduce a novel cosmological model that provides an effective description of the back-reaction of super-Hubble fluctuations on the cosmological background, a generic effect expected to arise in any cosmological scenario without requiring additional ingredients. At the phenomenological level, it can be interpreted as an interacting dark sector scenario in which the sign of the energy transfer changes periodically over time. We constrain the model using CMB, BAO, and Type Ia supernova data. We find that a significant amplitude of the oscillatory interaction is allowed by the data, although there is no statistically significant preference for this model over $Λ$CDM.

astro-ph.CO↗

arXiv2025

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

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 $Λ\text{CDM}$ 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.

astro-ph.CO↗