Velocity-dependent interacting dark energy and dark matter with a Lagrangian description of perfect fluids

Abstract

We consider a cosmological scenario where the dark sector is described by two perfect fluids that interact through a velocity-dependent coupling. This coupling gives rise to an interaction in the dark sector driven by the relative velocity of the components, thus making the background evolution oblivious to the interaction and only the perturbed Euler equations are affected at first order. We obtain the equations governing this system with the Schutz-Sorkin Lagrangian formulation for perfect fluids and derive the corresponding stability conditions to avoid ghosts and Laplacian instabilities. As a particular example, we study a model where dark energy behaves as a radiation fluid at high redshift while it effectively becomes a cosmological constant in the late Universe. Within this scenario, we show that the interaction of both dark components leads to a suppression of the dark matter clustering at late times. We also argue the possibility that this suppression of clustering together with the additional dark radiation at early times can simultaneously alleviate the ${\sigma }_8$ and $H_0$ tensions.

22 pages, 12 figures, fixed minor typos

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• Cosmological direct detection of dark energy: non-linear structure formation signatures of dark energy scattering with visible matter
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• On Evidence for Elastic Interactions in the Dark Sector
• Cosmological Dynamics in Interacting Scalar-Torsion f(T,$\varphi$) Gravity: Investigating Energy and Momentum Couplings
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• Cosmological dynamical systems of non-minimally coupled fluids and scalar fields
• Dark sector interactions in the $w\to -1$ limit: velocity locking in pure momentum exchange models
• Revisiting observational constraints on coupled exponential quintessence with energy and momentum transfers: degeneracy with massive neutrinos