Amplitude Of Primordial Density Fluctuations Research Articles

Anthropic Prediction for Λ and theQCatastrophe

We discuss probability distributions for the cosmological constant Lambda and the amplitude of primordial density fluctuations Q in models where they both are anthropic variables. With mild assumptions about the prior probabilities, the distribution P(Lambda,Q) factorizes into two independent distributions for the variables Q and $y \propto \Lambda/Q^3$. The distribution for y is largely model-independent and is in a good agreement with the observed value of y. The form of P(Q) depends on the origin of density perturbations. If the perturbations are due to quantum fluctuations of the inflaton, then P(Q) tends to have an exponential dependence on Q, due to the fact that in such models Q is correlated with the amount of inflationary expansion. For simple models with a power-law potential, P(Q) is peaked at very small values of Q, far smaller than the observed value of 10^{-5}. This problem does not arise in curvaton-type models, where the inflationary expansion factor is not correlated with Q.

Neutrinos and physics beyond the standard model

A brief sketch is made of the present observational status of neutrino physics, with emphasis on the hints that follow from solar and atmospheric neutrino observations, as well as cosmological data on the amplitude of primordial density fluctuations. I also briefly review the ways to account for the observed anomalies and some of their implications.

Natural new inflation in broken supergravity

We consider a natural new inflationary model in broken supergravity based on an R symmetry. The model predicts a concrete relation between the amplitude of primordial density fluctuations and the scale of supersymmetry breaking. The observed value of the density fluctuations is obtained for the gravitino mass of order the weak scale along with a power-law spectral index considerably less than one, which may be tested in future observations.

Neutrino properties

A brief sketch is made of the present observational status of neutrino properties, with emphasis on the hints from solar and atmospheric neutrinos, as well as cosmological data on the amplitude of primordial density fluctuations. Implications of neutrino mass in particle accelerators, astrophysics and cosmology are discussed.

Large scale structure and supersymmetric inflation without fine tuning.

We explore constraints on the spectral index $n$ of density fluctuations and the neutrino energy density fraction ${\ensuremath{\Omega}}_{\ensuremath{\nu}}$ from observations of large scale structure. The best fits imply $n\ensuremath{\approx}1$ and ${\ensuremath{\Omega}}_{\ensuremath{\nu}}\ensuremath{\approx}0.1\ensuremath{-}0.3$, for Hubble constants 40-60 km ${\mathrm{s}}^{\ensuremath{-}1}$ ${\mathrm{Mpc}}^{\ensuremath{-}1}$. We present a new class of inflationary models based on realistic supersymmetric grand unified theories (GUTs) which do not have the usual "fine tuning" problems. The amplitude of primordial density fluctuations is found to be $\ensuremath{\propto}{(\frac{{M}_{X}}{{M}_{P}})}^{2}$, where ${M}_{X}$ (${M}_{P}$) denote the GUT (Planck) scale. The spectral index $n=0.98$, in excellent agreement with the observations.

Constraints on the amplitude of primordial density fluctuations from the large-scale cosmic microwave background temperature distribution

A general method for evaluating the maximum amplitude eta(H) of density fluctuations at their horizon crossing is presented that is consistent with all the available observations of the cosmic microwave background (CMB) large-scale temperature distribution. Flat universes with Gaussian, adiabatic, scale-invariant primordial density fluctuations are considered. The theoretical predictions are compared with the upper bounds on the CMB quadrupole anisotropy, the CMB anisotropy on intermediate angular scales, and the CMB autocorrelation function. It is found that the Fixen et al. (1983) upper limit on 10 degrees implies, at the 95 percent confidence level, eta(H) less than 0.00003. 25 refs.

Galaxy clusters and the amplitude of primordial fluctuations

view Abstract Citations (268) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galaxy Clusters and the Amplitude of Primordial Fluctuations Frenk, Carlos S. ; White, Simon D. M. ; Efstathiou, George ; Davis, Marc Abstract The distributions of velocity dispersion, gas temperature, and mass-to- light ratio for Abell clusters can be used to constrain the amplitude of primordial density fluctuations within hierarchical clustering theories for the formation of cosmic structure. We have calculated these distributions in the "standard" cold dark matter (CDM) cosmogony with the dual aim of testing the validity of this model and of fixing the value of the biasing parameter, b, which quantifies the segregation between galaxies and mass. To compare the model predictions with optical data, we construct catalogs of "galaxies" from N-body simulations, we subject them to projection effects similar to those in Abell's cluster catalog, and we estimate velocity dispersions using the techniques employed in analyses of real clusters. We find that a significant fraction of rich clusters identified in projection do not correspond to rich three-dimensional clusters, but result instead from superpositions of foreground groups on poorer clusters. A similar fraction of true rich clusters are missed in the projected catalogs. Projection effects have a dramatic effect on the predicted distribution of cluster velocity dispersions. The observed distribution, including a significant tail above ~1500 km s^-1^ is reproduced by our strongly biased CDM models (b ~ 2-2.5) even though these models predict only a negligible abundance of clusters with true dispersions larger than 1000 km s^-1^. The temperature of the X-ray-emitting gas in clusters is not affected by projection effects, but a comparison with theoretical predictions is hampered by selection effects in existing data and by uncertainties in the thermodynamic state of the gas. Combining our simulations with recent hydrodynamical models, we find that CDM models with b ~ 2-2.5 provide an acceptable match to present data. The most reliable constraint on b may come from the mean mass-to-light ratio of clusters which appears less sensitive to systematic observational errors than the distributions of velocity dispersions and X-ray temperatures. This comparison also suggests b ~ 2-3. Finally, we discuss theoretical expectations and possible observational problems associated with the study of clusters at intermediate and high redshifts. Optical studies of high- redshift clusters are unlikely to constrain b significantly, but X-ray studies seem more promising. Our results differ from those of other authors largely as a result of our detailed modeling of observational procedures. Publication: The Astrophysical Journal Pub Date: March 1990 DOI: 10.1086/168439 Bibcode: 1990ApJ...351...10F Keywords: Computational Astrophysics; Cosmology; Dark Matter; Galactic Clusters; Galactic Evolution; Line Of Sight; Many Body Problem; Mass To Light Ratios; Velocity Distribution; X Ray Spectra; Astrophysics; COSMOLOGY; DARK MATTER; GALAXIES: CLUSTERING; GALAXIES: REDSHIFTS; NUMERICAL METHODS full text sources ADS |

Massive superclusters as a probe of the nature and amplitude of primordial density fluctuations

It is pointed out that correlation studies of galaxy positions have been widely used in the search for information about the large-scale matter distribution. The study of rare condensations on large scales provides an approach to extend the existing knowledge of large-scale structure into the weakly clustered regime. Shane (1975) provides a description of several apparent massive condensations within the Shane-Wirtanen catalog, taking into account the Serpens-Virgo cloud and the Corona cloud. In the present study, a description is given of a model for estimating the frequency of condensations which evolve from initially Gaussian fluctuations. This model is applied to the Corona cloud to estimate its 'rareness' and thereby estimate the rms density contrast on this mass scale. An attempt is made to find a conflict between the density fluctuations derived from the Corona cloud and independent constraints. A comparison is conducted of the estimate and the density fluctuations predicted to arise in a universe dominated by cold dark matter.