Perturbations in cosmologies with a scalar field and a perfect fluid

  title={Perturbations in cosmologies with a scalar field and a perfect fluid},
  author={Nicola Bartolo and Pier Stefano Corasaniti and Andrew R. Liddle and Michael Malquarti},
  journal={Physical Review D},
We study the properties of cosmological density perturbations in a multi-component system consisting of a scalar field and a perfect fluid. We discuss the number of degrees of freedom completely describing the system, introduce a full set of dynamical gauge-invariant equations in terms of the curvature and entropy perturbations, and display an efficient formulation of these equations as a first-order system linked by a fairly sparse matrix. Our formalism includes spatial gradients, extending… 

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