Dark matter solution to the H0 and S8 tensions, and the integrated Sachs-Wolfe void anomaly

We consider a phenomenological model of dark matter with an equation-of-state w that is negative and changing at late times. We show this couples the H₀ and S₈ tensions, alleviating them both simultaneously, reducing the H₀ tension from ∼5 σ to ∼3 σ and the S₈ tension from ∼3 σ to ∼1 σ . Furthermore, the model provides an explanation for the anomalously large integrated Sachs-Wolfe (ISW) effect from cosmic voids, a unique consequence of the changing and negative equation-of-state. Observations of high ISW from cosmic voids may therefore be evidence that dark matter plays a significant role in both the H₀ and S₈ tensions. We predict the ISW from cosmic voids to be a factor of up to ∼2 greater in this model than what is expected from the standard model Λ CDM . These results extend to other degenerate models of dark matter, such as unified or interacting dark matter and dark energy models.