Large-scale instability in interacting dark energy and dark matter fluids

By Jussi Väliviita, E. Majerotto, R. Maartens. 2008

344 citations recorded by the source corpus.

If dark energy interacts with dark matter, this gives a new approach to the coincidence problem. But interacting dark energy models can suffer from pathologies. We consider the case where the dark energy is modelled as a fluid with constant equation of state parameter w. Non-interacting constant-w models are well behaved in the background and in the perturbed universe. But the combination of constant w and a simple interaction with dark matter leads to an instability in the dark sector perturbations at early times: the curvature perturbation blows up on super-Hubble scales. Our results underline how important it is to carefully analyse the relativistic perturbations when considering models of coupled dark energy. The instability that we find has been missed in some previous work where the perturbations were not consistently treated. The unstable mode dominates even if adiabatic initial conditions are used. The instability also arises regardless of how weak the coupling is. This non-adiabatic instability is different from previously discovered adiabatic instabilities on small scales in the strong-coupling regime.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/a1c48e5804df4b0755f1aa4778c301ea3edce88c

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Citations in the corpus

Nonminimal dark sector physics and cosmological tensions (2019, background): “Apart from the gravitational instabilities present when w = −1 [151, 228], there may also be early-time instabilities [151, 152, 157, 227–229], and avoiding them leads to imposing stability conditions on w and ξ.”
Interacting scenarios with dynamical dark energy: Observational constraints and alleviation of the H0 tension (2019, background): “Additionally, for an interacting universe the conservation equations become [103, 104, 105]”
Cosmology and Fundamental Physics with the Euclid Satellite (2012, methodology): “Alternatively, the coupling can be introduced by choosing directly a covariant stressenergy tensor, treating dark energy as a fluid in the absence of a starting action [818, 1189, 260, 1048, 1188, 811, 512, 259, 513].”
Alleviating the H0 and σ8 anomalies with a decaying dark matter model (2019, methodology): “We considered dark matter that decays into dark radiation, parameterised by a single new parameter [39, 46].”
Interacting dark energy in the early 2020s: A promising solution to the H0 and cosmic shear tensions (2019, methodology): “interacting vacuum), IDE models can suffer from gravitational instabilities [144, 265].”
Interacting dark energy with time varying equation of state and the H0 tension (2018, methodology): “For simplicity, we assume that momentum transfer potential is zero in the rest frame of the dark matter [51, 52, 53] which directs k(2)fA = QA(θ − θc) where k is the wave number and θ = θ μ, θc are respectively the volume expansion scalar of the total fluid and the volume expansion scalar for the CD”