Is there Another Solution To S8 Tension? (Cosmology)

Matteo lucca proposed dark energy-dark matter interactions as a possible solution to the S8 tension

Matteo Lucca investigated dark energy-dark matter interaction as a possible solution to the S8 tension. In particular, in order to address S8 tension, he proposed a scenario in which dark energy is a dynamical fluid, whose energy density can be transferred to the dark matter via a coupling function proportional to the energy density of the dark energy. Their study recently appeared in Arxiv.

Not just dark energy-dark matter interaction, several researchers also considered dark matter-dark energy interaction scenario. But, the cosmological features of both interactions are diametrically differ from each other depending on whether the energy density is flowing from the DE to the DM or vice versa.

In dark energy-dark matter interaction (iDEDM), because of the additional energy injected from the DE into the DM over the cosmic history, there has an overall suppression of the DM energy density with respect to the ΛCDM scenario. As a consequence, this results on the one hand in a decreased value of the Hubble parameter at late times, worsening the Hubble tension, and on the other hand in a delay of the radiation-matter equality from which follows a suppression of the matter power spectrum, which can alleviate the S8 tension. The opposite is true for the dark matter-dark energy interaction (iDMDE) case.

For these reasons, great attention has been dedicated to the iDMDE model in the context of the Hubble tension, although it has been explicitly shown by Lucca and Hooper in their previous study that, also this particular interacting DE scenario is unable to address the Hubble tension due to the no-go theorem that arises when Baryon Acoustic Oscillation (BAO) and SNIa data are accounted for. However, surprisingly, to his knowledge the iDEDM scenario has never been thoroughly investigated as a possible solution to the S8 tension. Thus, this inspired him to undertake this task in this study.

He found that, against data from Planck, BAO and Pantheon, the model

  • can significantly reduce the significance of the tension,
  • does so without exacerbating nor introducing any other tension (such as the H0 tension) and,
  • without worsening the fit to the considered data sets with respect to the ΛCDM model.

He also tested the model against data from weak lensing surveys such as KiDS and DES, and found that the model’s ability to address the S8 tension further improves, without a significant impact on any other parameter nor statistical measure.


Reference: Matteo Lucca, “Dark energy-dark matter interactions as a solution to the S8 tension”, Arxiv, pp. 1-7, 2021. https://arxiv.org/abs/2105.09249


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