Fluidflow description of density irregularities in the Universe
Abstract
A new derivation is given of two differential equations for the energydensity irregularities in the Universe, defined on a comoving hypersurface. One of them, a secondorder equation, is valid generally and the other, a firstorder equation, is valid when ∇^{2}P is negligible where P is the pressure. The new derivation of these important equations uses the fluidflow equations as advocated by Hawking in 1966, and is much simpler than the usual one involving metric perturbations. The regime of validity of the firstorder equation is discussed in some detail.
 Publication:

Physical Review D
 Pub Date:
 July 1988
 DOI:
 10.1103/PhysRevD.38.485
 Bibcode:
 1988PhRvD..38..485L
 Keywords:

 04.20.Cv;
 98.80.Dr;
 Fundamental problems and general formalism