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Cosmological perturbations
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 metricExpand
A general proof of the conservation of the curvature perturbation
Without invoking a perturbative expansion, we define the cosmological curvature perturbation, and consider its behaviour assuming that the universe is smooth over a sufficiently large comoving scale.Expand
A New approach to the evolution of cosmological perturbations on large scales
We discuss the evolution of linear perturbations about a Friedmann-Robertson-Walker background metric, using only the local conservation of energy-momentum. We show that on sufficiently large scalesExpand
Evolution of second-order cosmological perturbations.
We present a method for constructing gauge-invariant cosmological perturbations which are gauge-invariant up to second order. As an example, we give the gauge-invariant definition of the second-orderExpand
Non-Gaussianity of inflationary field perturbations from the field equation
We calculate the tree-level bispectrum of the inflaton field perturbation directly from the field equations, and construct the corresponding fNL parameter. Our results agree with previous onesExpand
A not so short note on the Klein–Gordon equation at second order
We give the governing equations for multiple scalar fields in a flat Friedmann–Robertson–Walker (FRW) background spacetime on all scales, allowing for metric and field perturbations up to secondExpand
Cosmological Perturbations in an Inflationary Universe
After introducing gauge-invariant cosmological perturbation theory we give an improved set of governing equations for multiple fluids including energy transfer. Having defined adiabatic and entropicExpand
Generalised constraints on the curvature perturbation from primordial black holes
Primordial black holes (PBHs) can form in the early Universe via the collapse of large density perturbations. There are tight constraints on the abundance of PBHs formed due to their gravitationalExpand
New calculation of the mass fraction of primordial black holes
We revisit the calculation of the abundance of primordial black holes (PBHs) formed from primordial density perturbations, using a formation criterion derived by Shibata and Sasaki which refers to aExpand
Large scale curvature and entropy perturbations for multiple interacting fluids
We present a gauge-invariant formalism to study the evolution of curvature perturbations in a Friedmann-Robertson-Walker universe filled by multiple interacting fluids. We resolve arbitraryExpand