Collisionless damping of density fluctuations in an expanding universe

Journal Article · Tue Nov 15 00:00:00 EST 1983 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/161460· OSTI ID:6623714

Bond, J R; Szalay, A S

The best candidate for the dark matter is a massive collisionless non-baryonic relic of the early universe. The most natural type of initial density fluctuations expected are of the adiabatic rather than of the isothermal type. We calculate the temporal evolution of the (initially adiabatic) fluctuation spectrum by numerical integration of the coupled Einstein-Boltzmann equations for scalar perturbations in the metric and in the density of photons, neutrinos, and collisionless relics. Our output linear perturbation spectrum, which is itself input to the nonlinear problem of large scale structure formation, is shown to be characterized by two scales: the damping mass and the horizon mass when the energy density in relativistic particles equals that in nonrelativistic ones, M/sub H/eq. Collisionless relics which decouple when relativistic may be of two basic types if they are to dominate the mass of the universe: massive neutrinos of 10--100 eV, or massive gravitinos (or other weakly interacting particles) of mass about 1 keV. For massive neutrinos, both scales are of supercluster size; and the Zel'dovich pancake picture, in which a large scale is the first to collapse, is expected, regardless of initial spectrum. For massive gravitinos, the damping mass is of galactic scale. Depending upon the initial spectrum, one can get either hierarchical clustering from the damping scale upward or fragmentation of the large M/sub H/eq scale. Collisionless relics which decouple when nonrelativistic have negligible damping masses; again, hierarchical clustering from very small scales or large scale fragmentation is possible in this adiabatic picture.

• Research Organization: Institute of Theoretical Physics, Department of Physics, Stanford University
• DOE Contract Number: AC02-80ER10773
• OSTI ID: 6623714
• Journal Information: Astrophys. J.; (United States), Vol. 274:2
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMOLOGICAL MODELS
ELEMENTARY PARTICLES
NEUTRINOS
UNIVERSE
BARYONS
BOLTZMANN EQUATION
COSMOLOGY
DAMPING
DISTURBANCES
EINSTEIN FIELD EQUATIONS
EXPANSION
GENERAL RELATIVITY THEORY
METRICS
PHOTONS
SPECTRA
DIFFERENTIAL EQUATIONS
EQUATIONS
FERMIONS
FIELD EQUATIONS
FIELD THEORIES
HADRONS
LEPTONS
MASSLESS PARTICLES
MATHEMATICAL MODELS
PARTIAL DIFFERENTIAL EQUATIONS
640106* - Astrophysics & Cosmology- Cosmology