The clustering of critical points in the evolving cosmic web

ABSTRACT Focusing on both small separations and baryonic acoustic oscillation scales, the cosmic evolution of the clustering properties of peak, void, wall, and filament-type critical points is measured using two-point correlation functions in ΛCDM dark matter simulations as a function of their relative rarity. A qualitative comparison to the corresponding theory for Gaussian random fields allows us to understand the following observed features: (i) the appearance of an exclusion zone at small separation, whose size depends both on rarity and signature (i.e. the number of negative eigenvalues) of the critical points involved; (ii) the amplification of the baryonic acoustic oscillation bump with rarity and its reversal for cross-correlations involving negatively biased critical points; (iii) the orientation-dependent small-separation divergence of the cross-correlations of peaks and filaments (respectively voids and walls) that reflects the relative loci of such points in the filament’s (respectively wall’s) eigenframe. The (cross-) correlations involving the most non-linear critical points (peaks, voids) display significant variation with redshift, while those involving less non-linear critical points seem mostly insensitive to redshift evolution, which should prove advantageous to model. The ratios of distances to the maxima of the peak-to-wall and peak-to-void over that of the peak-to-filament cross-correlation are ${\sim} \sqrt{2}$ and ${\sim} \sqrt{3}$, respectively, which could be interpreted as the cosmic crystal being on average close to a cubic lattice. The insensitivity to redshift evolution suggests that the absolute and relative clustering of critical points could become a topologically robust alternative to standard clustering techniques when analysing upcoming surveys such as Euclid or Large Synoptic Survey Telescope (LSST).

Alcock–Paczyński test with model-independent BAO data

Cosmological tests based on the statistical analysis of galaxy distributions usually depend on source evolution. An exception is the Alcock–Paczyński (AP) test, which is based on the changing ratio of angular to spatial/redshift size of (presumed) spherically-symmetric source distributions with distance. Intrinsic redshift distortions due to gravitational effects may also have an influence, but they can now be overcome with the inclusion of a sharp feature, such as the Baryonic Acoustic Oscillation (BAO) peak. Redshift distortions affect the amplitude of the peak, but impact its position only negligibly. As we shall show here, the use of this diagnostic, with new BAO peaks from SDSS-III/BOSS at average redshifts [Formula: see text], [Formula: see text] and [Formula: see text], disfavors the current concordance ([Formula: see text]CDM) model at [Formula: see text]. Within the context of expanding Friedmann–Robertson–Walker (FRW) cosmologies, these data instead favor the zero active mass equation-of-state, [Formula: see text], where [Formula: see text] and [Formula: see text] are, respectively, the total density and pressure of the cosmic fluid, the basis for the [Formula: see text] universe.

THE RANKING OF f(R) THEORIES AMONG ALTERNATIVE COSMOLOGICAL SCENARIOS

There are many cosmological scenarios that try to explain the observed current accelerated expansion. They are based or on the existence of new fields in nature or on the modification of the gravitation theory. This work investigates the observational viability of a modified gravity f(R) = R - α/ Rn within the Palatine approach, in the light of 32 age measurements of passively evolving galaxies and the baryonic acoustic oscillation peak scale. By using information-criteria model selection, this scenario is compared with the DGP alternative cosmological model as well the adjustable components of energy based in the general relativity based int the observational data set.