The effective field theory of multi-component fluids

Abstract

We study the effective Lagrangian, at leading order in derivatives, that describes the propagation of density and metric fluctuations in a fluid composed by an arbitrary number of interacting components. Our results can be applied to any situation in cosmology where different species have non-gravitational interactions. In time-dependent backgrounds, such as FLRW, the quadratic action can only be diagonalized at fixed time slices and flavour mixing is unavoidable as time flows. In spite of this, the fluid can be interpreted at the level of the linear equations of motion as an ensemble of individual interacting species. We show that interactions lead to anisotropic stresses that depend on the mixing terms in the quadratic action for perturbations. In addition to the standard entrainment among different components, we find a new operator in the effective action that behaves as a cosmological constant when it dominates the dynamics.

1+19 pages. Minor changes. Matches JCAP version

References in corpus (7)

• The Effective Field Theory of Inflation
• Effective Field Theory for Inflation
• Theoretical Models of Dark Energy
• The quantum mechanics of perfect fluids
• Coupled dark matter-dark energy in light of near Universe observations
• Future weak lensing constraints in a dark coupled universe
• Constraining the dark fluid

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• Thermodynamics of perfect fluids from scalar field theory
• Velocity-dependent interacting dark energy and dark matter with a Lagrangian description of perfect fluids
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• Cascading dust inflation in Born-Infeld gravity
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