Pancake Model Research Articles

Nonlinear evolution of large-scale structure in the universe

Using N-body simulations we study the nonlinear development of primordial density perturbation in an Einstein--de Sitter universe. We compare the evolution of an initial distribution without small-scale density fluctuations to evolution from a random Poisson distribution. These initial conditions mimic the assumptions of the adiabatic and isothermal theories of galaxy formation. The large-scale structures which form in the two cases are markedly dissimilar. In particular, the correlation function xi(r) and the visual appearance of our adiabatic (or ''pancake'') models match better the observed distribution of galaxies. This distribution is characterized by large-scale filamentary structure. Because the pancake models do not evolve in a self-similar fashion, the slope of xi(r) steepens with time; as a result there is a unique epoch at which these models fit the galaxy observations. We find the ratio of cutoff length to correlation length at this time to be lambda/sub min//r/sub 0/ = 5.1; its expected value in a neutrino dominated universe is 4(..cap omega..h)/sup -1/ (H/sub 0/ = 100h km s/sup -1/ Mpc/sup -1/). At early epochs these models predict a negligible amplitude for xi(r) and could explain the lack of measurable clustering in the Ly..cap alpha.. absorption lines of high-redshift quasars. However, large-scale structuremore » in our models collapses after z = 2. If this collapse precedes galaxy formation as in the usual pancake theory, galaxies formed uncomfortably recently. The extent of this problem may depend on the cosmological model used; the present series of experiments should be extended in the future to include models with ..cap omega..<1.« less

Propagation of adiabatic cosmological perturbations through the ERA of matter-radiation decoupling

view Abstract Citations (84) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Propagation of adiabatic cosmological perturbations through the ERA of matter-radiation decoupling Press, W. H. ; Vishniac, E. T. Abstract With particular reference to the pancake theory of galaxy formation, the paper calculates the attenuation or amplification of adiabatic perturbations of a Friedmann cosmology before, during, and after the era of hydrogen recombination and matter-radiation decoupling. The calculation is based on a modified two-fluid (baryon, photon) model which maintains accuracy even when the mean free path of the photon fluid becomes arbitrarily large. It is found that in addition to the damping of radiative viscosity and heat conduction before recombination, damping just during decoupling is important. Consequently there is no 'velocity overshoot' of perturbations to increased amplitude (as had been previously proposed); this probably renders the standard pancake model inconsistent with present limits on the microwave anisotropy. Also, the smallest surviving mass scales ('pancake masses') are quite large, e.g., 2 x 10 to the 16th solar masses, about 120 Mpc, for Omega = 0.1. Publication: The Astrophysical Journal Pub Date: March 1980 DOI: 10.1086/157749 Bibcode: 1980ApJ...236..323P Keywords: Cosmology; Galactic Evolution; Hydrodynamic Equations; Perturbation Theory; Two Fluid Models; Adiabatic Conditions; Conductive Heat Transfer; Differential Equations; Hydrogen Recombinations; Astrophysics full text sources ADS |

Spontaneous Production of the Zel'dovich Spectrum of Cosmological Fluctuations

The spectrum of initial cosmological perturbations posited by Zel'dovich and co-workers for the "pancake theory" of galaxy formation has (i) adiabatic perturbations only, and (ii) constant perturbation amplitude on all scales at their respective horizon times. Assumption (i) has recently been shown to follow from grand unified gauge theories. This paper shows that assumption (ii) may also be a consequence of spontaneous symmetry-breaking at sufficiently high temperatures. In this case the Universe may have been exactly Friedmannian originally. In a classical, U(1) Abelian Higgs model, the scale-independent dimensionless size of perturbations is here calculated to be δT00/T00 ∼ (8π/3)(Tc/m*)2 where m* is the Planck mass (1019 GeV) and Tc is the critical temperature of spontaneous symmetry-breaking, related to the mass of the gauge boson of the symmetry group. For the pancake model, one needs Tc ∼ 1017 GeV.