Cosmological perturbations

By Karim A. Malik, D. Wands. Series on the Foundations of Natural Science and Technology, 2008

443 citations recorded by the source corpus.

We review the study of inhomogeneous perturbations about a homogeneous and isotropic background cosmology. We adopt a coordinate based approach, but give geometrical interpretations of metric perturbations in terms of the expansion, shear and curvature of constant-time hypersurfaces and the orthogonal timelike vector field. We give the gauge transformation rules for metric and matter variables at first and second order. We show how gauge invariant variables are constructed by identifying geometric or matter variables in physically-defined coordinate systems, and give the relations between many commonly used gauge-invariant variables. In particular we show how the Einstein equations or energy-momentum conservation can be used to obtain simple evolution equations at linear order, and discuss extensions to non-linear order. We present evolution equations for systems with multiple interacting fluids and scalar fields, identifying adiabatic and entropy perturbations. As an application we consider the origin of primordial curvature and isocurvature perturbations from field perturbations during inflation in the very early universe.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b6d1d42e0b41989de94295c8963b994f7eb6906a

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Citations in the corpus

Interacting scenarios with dynamical dark energy: Observational constraints and alleviation of the H0 tension (2019, background): “Let us briefly describe the perturbation equations for an interacting dark energy model following [100, 101, 102].”
Interacting dark sector and precision cosmology (2017, background): “J C A P 0 1 ( 2 0 1 8 ) 0 0 8 Following for example [64, 65], consider two fluids A and B which interact with one another respecting overall energy-momentum conservation, ∇μ ( T A + T μν B ) = 0.”
Gravitational wave decay into dark energy (2018, background): “[50]), where the metric is written in the general decomposition”
Gravitational waves from a universe filled with primordial black holes (2020, background): “Let us now express the density contrast in different gauges [56].”
Gravitational wave constraints on the primordial black hole dominated early universe (2020, background): “Note that the choice of the synchronous comoving gauge is possible since the PBH gas behaves as dust [77].”
Interacting dark energy with time varying equation of state and the H0 tension (2018, background): “In what follows, we consider the perturbed FLRW metric [48, 49, 50]”