(5b) A Convenient Set of Comoving Cosmological Variables
and Their Application
Martel and Shapiro (1998) generalized the comoving variables
presented by Shandarin (1980) for matter-dominated models to
cosmological models in which there is an additional, nonclumping background
energy density, such as a cosmological constant. Such models are of great
current interest because they help reconcile the CDM model of structure
formation with data on galaxy clustering and large-scale structure, the COBE
CMB temperature anisotropy measurement, the average estimates of the age of
globular clusters, the Hubble constant, and dynamical estimates of the mean
cosmic matter density. When written in these new, "supercomoving" variables,
the cosmological fluid equations for a nonrelativistic, gamma=5/3
gas become identical with noncosmological fluid equations, making the
application of familiar results and techniques from noncosmological gas
dynamics straightforward.