Multi-frequency search for Dark Matter: the role of HESS, CTA, and SKA

Dark Matter (DM) remains a vital, but elusive, component in our current understanding of the universe. Accordingly, many experimental searches are devoted to uncovering its nature. However, both the existing direct detection methods, and the prominent $\gamma$-ray search with the Fermi Large Area Telescope (Fermi-LAT), are most sensitive to DM particles with masses below 1 TeV, and are significantly less sensitive to the hard spectra produced in annihilation via heavy leptons. The High Energy Stereoscopic System (HESS) has had some success in improving on the Fermi-LAT search for higher mass DM particles, particularly annihilating via heavy lepton states. However, the recent discovery of high J-factor dwarf spheroidal galaxies by the Dark Energy Survey (DES) opens up the possibility of investing more HESS observation time in the search for DM $\gamma$-ray signatures in dwarf galaxies. This work explores the potential of HESS to extend its current limits using these new targets, as well as the future constraints derivable with the up-coming Cherenkov Telescope Array (CTA). These limits are further compared with those we derived at low radio frequencies for the Square Kilometre Array (SKA). Finally, we explore the impact of HESS, CTA, and Fermi-LAT on the phenomenology of the "Madala" boson hypothesized based on anomalies in the data from the Large Hadron Collider (LHC) run 1. The power of these limits from differing frequency bands is suggestive of a highly effective multi-frequency DM hunt strategy making use of both existing and up-coming Southern African telescopes.Comment: 11 pages, 5 figures, 1 table. To appear in Proceedings of Science: High Energy Astrophysics in South Africa 201

Velocity correlation tensor and substructure's statistics around density peaks

We derive the conditional probability distribution of the peculiar velocity around a peak of given overdensity in a Gaussian density field. This distribution characterizes the shear field around local, isolated density peaks. We use the moments of the velocity distribution to study the spatial distribution of the escape velocity from protostructures forming in a standard, flat, scale--invariant CDM model. In the case of high (\nu \sim 2) peaks with filtering scales R_f \sim 2 h^{-1}~\mbox{Mpc}, we find that at distances between 2 \div 4~{\rm \mbox{Mpc}~h^{-1}} (or equivalently \approx 1 \div 2 ~R_f) a sensitive fraction of the matter enclosed within an extrapolated (up to the present epoch) volume containing a total gravitating mass M \approx 2.725\times10^{15} h^{-1} M_{\odot} (of the same order as that derived from gravitational lensing observations, see Tyson and Fisher~\cite{tf95}) is {\em gravitationally unbound} to the peak. The fraction of unbound matter varies between approximately between 0.05-0.2 depending on the central height \nu of the density peak, on the filtering radius and on the adopted normalization for the fluctuation spectrum. We show how these results support our previous conclusions regarding the delay of the collapse induced by the presence of small-scale substructure in clusters of galaxies formed in standard CDM cosmological models

Multi-Frequency Study of the SZ Effect in Cosmic Structures

The Sunyaev-Zel’dovich effect (SZE) is a relevant probe for cosmology and astrophysics. A multi-frequency approach to study the SZE in cosmic structures turns out to be crucial in the use of this probe for astrophysics and cosmology. Astrophysical and cosmological applications to galaxy clusters, galaxies, radiogalaxies and large-scale structures are discussed. Future directions for the study of the SZE and its polarization are finally outlined

THE SZ EFFECT IN THE PLANCK ERA: ASTROPHYSICAL AND COSMOLOGICAL IMPACT

The Sunyaev–Zel’dovich effect (SZE) is a relevant probe for cosmology and particle astrophysics. The Planck Era marks a definite step forward in the use of this probe for astrophysics and cosmology. Astrophysical applications to galaxy clusters, galaxies, radiogalaxies and large-scale structures are discussed. Cosmological relevance for the Dark Energy equation of state, modified Gravity scenarios, Dark Matter search, cosmic magnetism and other cosmological applications is also reviewed. Future directions for the study of the SZE and its polarization are finally outlined