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The high-mass end of the halo mass function is a sensitive probe of primordial non-Gaussianity (NG). In a recent study [9], we have computed the NG halo mass function in the context of the excursion set theory and shown that the primordial NG imprint is coupled to that induced by the nonlinear collapse of dark matter halos. We also found an excellent agreement with N-body simulation results. Here, we perform a more accurate computation which accounts for the interval validity of the bispectrum expansion to next-to-leading order and extend the calculation to the case of a nonvanishing primordial trispectrum. [ABSTRACT FROM AUTHOR]

The growth rate of cosmic structure is a powerful cosmological probe for extracting information on the gravitational interactions and dark energy. In the late-time Universe, the growth rate becomes nonlinear and is usually probed by measuring the two-point statistics of galaxy clustering in redshift space up to a limited scale, retaining the constraint on the linear growth rate f. In this paper, we present an alternative method to analyze the growth of structure in terms of local densities, i.e., f(Δ). Using N-body simulations, we measure the function of f(Δ) and show that structure grows faster in high-density regions and slower in low-density regions. We demonstrate that f(Δ) can be modeled using a log-normal Monte Carlo random walk approach, which provides a means to extract cosmological information from f(Δ). We discuss prospects for applying this approach to galaxy surveys. [ABSTRACT FROM AUTHOR]

Using cosmic voids to probe the growth rate of cosmic structure, and hence the nature of dark energy, is particularly interesting in the context of modified gravity theories that rely on the "screening mechanism." In this work we improve the modelling of redshift-space distortions around voids in the dark matter density field, and thus reduce systematic errors in the derivation of cosmological parameters. We also show how specific types of voids can be used to better probe the growth rate, using a flexible void finder. We apply our results to test for a "quintessence" type of dark energy vs. a Λ CDM model, and find a good agreement with the fiducial cosmology after implementing an analytical correction to the radial velocity profiles around voids. We additionally outline characteristic imprints of dark energy in the dark matter velocity distributions around voids. [ABSTRACT FROM AUTHOR]

Using Monte Carlo random walks of a log-normal distribution, we show how to qualitatively study void properties for nonstandard cosmologies. We apply this method to an f(R) modified gravity model and recover the N-body simulation results of [I. Achitouv, M. Baldi, E. Puchwein, and J. Weller, Phys. Rev. D 93, 103522 (2016).] for the void profiles and their deviation from GR. This method can potentially be extended to study other properties of the large scale structures such as the abundance of voids or overdense environments. We also introduce a new way to identify voids in the cosmic web, using only a few measurements of the density fluctuations around random positions. This algorithm allows us to select voids with specific profiles and radii. As a consequence, we can target classes of voids with higher differences between f(R) and standard gravity void profiles. Finally, we apply our void criteria to galaxy mock catalogues and discuss how the flexibility of our void finder can be used to reduce systematic errors when probing the growth rate in the galaxy-void correlation function. [ABSTRACT FROM AUTHOR]

The high-mass end of the halo mass function is a sensitive probe of primordial non-Gaussianity (NG). In a recent study [9], we have computed the NG halo mass function in the context of the excursion set theory and shown that the primordial NG imprint is coupled to that induced by the nonlinear collapse of dark matter halos. We also found an excellent agreement with N-body simulation results. Here, we perform a more accurate computation which accounts for the interval validity of the bispectrum expansion to next-to-leading order and extend the calculation to the case of a nonvanishing primordial trispectrum. [ABSTRACT FROM AUTHOR]

We compute the critical density of collapse for spherically symmetric overdensities in a class of f(R) modified gravity models. For the first time we evolve the Einstein, scalar field and nonlinear fluid equations, making the minimal simplifying assumptions that the metric potentials and scalar field remain quasistatic throughout the collapse. Initially evolving a top-hat profile, we find that the density threshold for collapse depends significantly on the initial conditions imposed, specifically the choice of size and shape. By imposing "natural" initial conditions, we obtain a fitting function for the spherical collapse Sc as a function of collapse redshift, mass of the overdensity and fR0, the background scalar field value at z = 0. By extending Sc into a drifting and diffusing barrier within the context of excursion set theory, we obtain a realistic mass function that might be used to confront this class of scalar-tensor models with observations of dark-matter halos. The proposed analytic formula for the halo mass function was tested against Monte Carlo random walks for a wide class of moving barriers and can therefore be applied to other modified gravity theories. [ABSTRACT FROM AUTHOR]

We calculate the halo correlation function in redshift space using the Gaussian streaming model (GSM). To determine the scale-dependent functions entering the GSM, we use local Lagrangian bias together with convolution Lagrangian perturbation theory (CLPT), which constitutes an approximation to the Post-Zel'dovich approximation. On the basis of N-body simulations, we demonstrate that a smoothing of the initial conditions with the Lagrangian radius improves the Zel'dovich approximation and its ability to predict the displacement field of protohalos. Based on this observation, we implement a "truncated" CLPT by smoothing the initial power spectrum and investigate the dependence of the streaming model ingredients on the smoothing scale. We find that the real space correlation functions of halos and their mean pairwise velocity are optimized if the coarse graining scale is chosen to be 1 Mpc/h at z=0, while the pairwise velocity dispersion is optimized if the smoothing scale is chosen to be the Lagrangian size of the halo. We compare theoretical results for the halo correlation function in redshift space to measurements within the Horizon run 2 N-body simulation halo catalog. We find that this simple two-filter smoothing procedure in the spirit of the truncated Zel'dovich approximation significantly improves the GSM+CLPT prediction of the redshift space halo correlation function over the whole mass range from large galaxy to galaxy cluster-sized halos. We expect that the necessity for two filter scales is an artifact of our local bias model, and that once a more physical bias model is implemented in CLPT, the only physically relevant smoothing scale will be related to the Lagrangian radius, in accord with our findings based on N-body simulations. [ABSTRACT FROM AUTHOR]

We compute the critical density of collapse for spherically symmetric overdensities in a class of f(R) modified gravity models. For the first time we evolve the Einstein, scalar field and nonlinear fluid equations, making the minimal simplifying assumptions that the metric potentials and scalar field remain quasistatic throughout the collapse. Initially evolving a top-hat profile, we find that the density threshold for collapse depends significantly on the initial conditions imposed, specifically the choice of size and shape. By imposing "natural" initial conditions, we obtain a fitting function for the spherical collapse dc as a function of collapse redshift, mass of the overdensity and fR0, the background scalar field value at z=0. By extending dc into a drifting and diffusing barrier within the context of excursion set theory, we obtain a realistic mass function that might be used to confront this class of scalar-tensor models with observations of dark-matter halos. The proposed analytic formula for the halo mass function was tested against Monte Carlo random walks for a wide class of moving barriers and can therefore be applied to other modified gravity theories. [ABSTRACT FROM AUTHOR]