Non-adiabatic perturbations in multi-component perfect fluids

Abstract

The evolution of non-adiabatic perturbations in models with multiple coupled perfect fluids with non-adiabatic sound speed is considered. Instead of splitting the entropy perturbation into relative and intrinsic parts, we introduce a set of symmetric quantities, which also govern the non-adiabatic pressure perturbation in models with energy transfer. We write the gauge invariant equations for the variables that determine on a large scale the non-adiabatic pressure perturbation and the rate of changes of the comoving curvature perturbation. The analysis of evolution of the non-adiabatic pressure perturbation has been made for several particular models.

11 pages, v2, major revision, some clarifications added, English is improved, results unchanged

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• An extensive investigation of the Generalised Dark Matter model
• Non-linear dark energy clustering
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• Revealing the non-adiabatic nature of dark energy perturbations from galaxy clustering data
• Degeneracy between nonadiabatic dark energy models and $\Lambda$CDM: ISW effect and the cross correlation of CMB with galaxy clustering data
• Velocity and Heat Flow in a Composite Two Fluid System
• Ultralight scalar dark matter versus nonadiabatic perfect fluid dark matter in pulsar timing