AR-2019-2020

10 − 18 10 − 15 10 − 12 10 − 9 10 − 6 10 − 3 10 0 10 3 M PBH /M 10 − 5 10 − 4 10 − 3 10 − 2 10 − 1 10 0 f PBH = Ω 0 , PBH / Ω 0 , DM 6 × 10 − 17 M 10 − 13 M 15 M PBH from KKLT inflation Figure 7: The fractional abundance of primordial black holes is shown as a function of PBH mass in the KKLT model for three differently located bumps. One sees that KKLT inflation with a tiny bump can generate nearly monochromatic narrow band mass functions, corresponding to 6 × 10 − 17 , 10 − 13 and 15 M black holes. PBHs in these bands can contribute significantly to the dark matter density in the universe today. Voronoi volume function: A new probe of cosmology and galaxy evolution Aseem Paranjape and Shadab Alam (Royal Observatory, Edinburgh) have proposed the Voronoi volume function, (VVF) described below, as a novel probe of cosmology and structure formation. For a collection of points in space, such as the locations of tracers like galaxies or dark matter haloes, the Voronoi tessellation is a unique partitioning of space into cells such that (a) each cell contains a single tracer, and (b) any point in a cell is closer to the tracer contained in that cell than to any other tracer in the set. The Voronoi tessellation has a long history of applications in many scientific fields, including cosmology and large-scale structure, where it has been previously used in void-finding algorithms and numerical simulation techniques. The VVF proposed by Paranjape and Alam is simply the distribution of cell volumes of the Voronoi tessellation of any given set of galaxies or galaxy-like objects. They show that the shape of the VVF of such tracers responds sensitively to physical proper- ties such as mass, large-scale environment, sub-structure and redshift-space effects, making this a hitherto unexplored probe of both primordial cosmology and galaxy evolution. Using convenient summary statistics the width, median and a low percentile of the VVF as functions of tracer num- ber density, they explore these effects using tessellations of tracers (specifically, dark matter haloes) identified in a suite of N-body simulations of a range of dark matter models. They find that the summary statistics are sensitive probes of primordial features such as small-scale oscillations in the initial matter power spectrum (as arise in models involving collisional effects in the dark sector), while being largely insensitive to a truncation of initial power (as in warm dark matter models). For vanilla Cold Dark Matter (CDM) cosmologies, the summary statistics display strong redshift evolu- tion and redshift-space effects, and are also sensitive to cosmological parameter values for realistic samples. Comparing the VVF of galaxies in the GAMA survey with that of abundance matched CDM (sub)haloes tentatively reveals environmental effects in GAMA beyond halo mass. Their exploratory analysis, thus, paves the way for using the VVF as a new probe of galaxy evolution