Theories which modify general relativity to explain the accelerated expansion of the Universe often use screening mechanisms to satisfy constraints on Solar System scales. We investigate the effects of the cosmic web and the local environmental density of dark matter halos on the screening properties of the Vainshtein and chameleon screening mechanisms. We compare the cosmic web morphology of d...

We examine the expected signal from annihilation events in realistic cold dark matter halos. If the WIMP is a neutralino, with an annihilation cross-section predicted in minimal SUSY models for the lightest stable relic particle, the central cusps and dense substructure seen in simulated halos may produce a substantial flux of energetic gamma rays. We derive expressions for the relative flux fr...

We study the angular momentum profile of dark matter halos for a statistical sample drawn from a set of high-resolution cosmological simulations of 256 3 particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and the halos are selected to have at least 3 × 10 4 particles in order to reliably measure the angular momentum profile. In contrast with the recent claims of Bullock et...

Despite the growing scientific awareness of ice-crystal halos, there is surprising lack of quantitative observational data about them. Even the most basic (and often-referenced) angular measurements sometimes consist of casual determinations of the radii of circular-halos with no mention whatever of the intensity distribution. More-complex halos are reported with either freehand drawings or pho...

N-body simulations of dark matter halos show that the density profiles of halos behave as ρ(r) ∝ r−α(r), where the density logarithmic slope α ≃ 1 ∼ 1.5 in the center and α ≃ 3 ∼ 4 in the outer parts of halos. However, some observations are not in agreement with simulations in the very central region of halos. The simulations also show that velocity dispersion anisotropy parameter β ≈ 0 in the ...

We have tried to understand the recent observations related to metallicity in Ly α forest clouds in the framework of the two component model suggested by Chiba & Nath (1997). The model consists of mini-halos having circular velocities smaller than ∼ 55 km s, with no star formation and galactic halos with higher circular velocities ≤ 250 km s, having clouds, star formation and consequent metal e...