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Author: Alexander Victorovich Shirokov Publisher: ISBN: Category : Languages : en Pages : 181
Book Description
(Cont.) It is shown in this thesis that inhomogeneous distribution of dark matter on small scales significantly changes the predicted event rates in direct detection dark matter experiments. The effect of spatial inhomogeneity weakens the upper limits on neutralino cross section produced in the Cryogenic Dark Matter Search Experiment.
Author: Alexander Victorovich Shirokov Publisher: ISBN: Category : Languages : en Pages : 181
Book Description
(Cont.) It is shown in this thesis that inhomogeneous distribution of dark matter on small scales significantly changes the predicted event rates in direct detection dark matter experiments. The effect of spatial inhomogeneity weakens the upper limits on neutralino cross section produced in the Cryogenic Dark Matter Search Experiment.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Cosmological simulations show that dark matter halos contain a wealth of substructure. These subhalos are assumed have a mass distribution that extends down to the smallest mass in the Cold Dark Matter (CDM) hierarchy, which lies below the current resolution limit of simulations. Substructure has important ramifications for indirect dark matter detection experiments as the signal depends sensitively on the small-scale density distribution of dark matter in the Galactic halo. A clumpy halo produces a stronger signal than halos where the density is a smooth function of radius. However, the small-scale Universe presents a daunting challenge for models of structure formation. In the CDM paradigm, structures form in a hierarchical fashion, with small-scale perturbations collapsing first to form halos that then grow via mergers. However, near the bottom of the hierarchy, dark matter structures form nearly simultaneously across a wide range of scales. To explore these small scales, I use a series of simulations of scale-free cosmological models, where the initial density power spectrum is a power-law. I can effectively examine various scales in the Universe by using the index in these artificial cosmologies as a proxy for scale. This approach is not new, but my simulations are larger than previous such simulations by a factor of 3 or more. My results call into question the often made assumption that the subhalo population is scale-free. The subhalo population does depend on the mass of the host. By combining my study with others, I construct a phenomenological model for the subhalo mass function. This model shows that the full subhalo hierarchy does not greatly boost the dark matter annihilation flux of a host halo. Thus, the enhancement of the Galactic halo signature due to substructure can not alone account the observed flux of cosmic rays produced by annihilating dark matter. Finally, I examine the nonlinear power spectrum, which is used to determine cosmological parame.
Author: Warren Richard Morningstar Publisher: ISBN: Category : Languages : en Pages :
Book Description
The standard model for dark matter, the Cold Dark Matter model, which accurately predicts the formation and evolution of large scale structure in the universe, appears to be in disagreement with observations of structure on much smaller scales. It is, as of yet, unclear if this is due to astrophysical processes causing a reduction in the efficiency of star formation in low mass galaxies, or due to the suppression of low mass structure formation altogether caused by exciting new dark matter microphysics. Gravitational lensing offers a unique and luminosity-independent means of distinguishing between these possibilities. In this work, I present tools to simulate realistic ALMA observations of strong gravitational lenses, and to model the small scale distribution of dark matter using interferometric observations of strong lenses. We applied this technique to observations of the gravitational lens SDP 81, and identified a low mass perturbing object, and placed new constraints on the abundance of low mass dark matter halos. I also present several techniques to automate the inference of the smooth distribution of matter in these objects, which allow inference to proceed 1.6 billion times faster, and which strongly reduce the need for human supervision of the modeling process. With these techniques in hand, we are poised to extract important information about the elusive dark matter.
Author: Siegfried Wagner Publisher: Springer Science & Business Media ISBN: 3540691820 Category : Mathematics Languages : en Pages : 700
Book Description
For the fourth time, the Leibniz Supercomputing Centre (LRZ) and the Com- tence Network for Technical, Scienti c High Performance Computing in Bavaria (KONWIHR) publishes the results from scienti c projects conducted on the c- puter systems HLRB I and II (High Performance Computer in Bavaria). This book reports the research carried out on the HLRB systems within the last three years and compiles the proceedings of the Third Joint HLRB and KONWIHR Result and Reviewing Workshop (3rd and 4th December 2007) in Garching. In 2000, HLRB I was the rst system in Europe that was capable of performing more than one Tera op/s or one billion oating point operations per second. In 2006 it was replaced by HLRB II. After a substantial upgrade it now achieves a peak performance of more than 62 Tera op/s. To install and operate this powerful system, LRZ had to move to its new facilities in Garching. However, the situation regarding the need for more computation cycles has not changed much since 2000. The demand for higher performance is still present, a trend that is likely to continue for the foreseeable future. Other resources like memory and disk space are currently in suf cient abundance on this new system.
Author: Carlos Chover Lopez Publisher: ISBN: Category : Languages : en Pages :
Book Description
In the last century, new observational techniques and discoveries such as the Cosmic Microwave Background Radiation have brought a new dimension of knowledge about the Universe. Therefore new theories and models have been proposed to explain the observed Universe. Computer simulations are a very important tool because they lay a bridge between theory, often over-simpli ed, and observations, which reveal the complexity of our Universe. In this thesis, it is given a review of observations including the most important discoveries and results that help to describe the Universe and have been used to develop the models considered nowadays. The cosmological theory behind the large-scale structure formation is explained, from the basis of the Friedman model to the formation of structures through the linear, quasi-linear and non-linear regime, including the Zeldovich approximation and the spherical collapse model. Furthermore, the di erent types of codes used for cosmological simulations are introduced, focusing on the N-body codes and presenting the code used in this thesis, developed by Klypin & Holtzman (1997). The tools used to analyse the results: density plots, power spectrum and mass variance are described as well. Three main sets of simulations have been performed: a basic simulation (RUN0) with standard cosmological parameters, simulations of CDM and simulations of Hot+Cold Dark Matter (HCDM). All the simulations use 323 particles, while di erent cosmological parameters have been changed e.g. 8, m, and n. Thus, it is observed that higher values of m and low values of lead to more clustering and hence more developed structures. Moreover, the e ect of 8 appears to be critical, since it determines the amplitude of the density uctuations at the initial redshift of the simulation. When studying the presence of hot dark matter, the main di erence comes from the cut-o in the power spectrum due to the hot dark matter free-streaming, resulting in less developed structures. Similarly to the previous case, the e ects of the cosmological parameters are explained for this model. Finally, some additional simulations regarding dark halos populations and density pro- les are included in the Appendix.
Author: Reuben David Blaff Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Cold dark matter (CDM) cosmological N-body simulations have proved to be powerful tools for studying the evolution and structure of the universe. These simulations, however, predict certain small-scale structure that disagrees with observation. They are also computationally expensive. Thus, the majority of efforts have focused upon the vanilla CDM model. There are, however, a variety of DM models beyond CDM, such as self-interacting dark matter (SIDM), which has shown promise in resolving some of the aforementioned small-scale structure problems. Our new Python package, SPHerical, which we present in this paper, aims to allow for further exploration of SIDM and other alternative DM models. The package is used to simulate the evolution of isolated spherically symmetric DM halos using a Smoothed Particle Hydrodynamics (SPH) framework and gravothermal fluid model. In this paper, we limit our scope to SIDM and compare SPHerical's results with those of similar simulations.
Author: Miguel A. Sánchez-Conde Publisher: MDPI ISBN: 3039360442 Category : Mathematics Languages : en Pages : 220
Book Description
An important, open research topic today is to understand the relevance that dark matter halo substructure may have for dark matter searches. In the standard cosmological model, halo substructure or subhalos are predicted to be largely abundant inside larger halos, for example, galaxies such as ours, and are thought to form first and later merge to form larger structures. Dwarf satellite galaxies—the most massive exponents of halo substructure in our own galaxy—are already known to be excellent targets for dark matter searches, and indeed, they are constantly scrutinized by current gamma-ray experiments in the search for dark matter signals. Lighter subhalos not massive enough to have a visible counterpart of stars and gas may be good targets as well, given their typical abundances and distances. In addition, the clumpy distribution of subhalos residing in larger halos may boost the dark matter signals considerably. In an era in which gamma-ray experiments possess, for the first time, the exciting potential to put to test the preferred dark matter particle theories, a profound knowledge of dark matter astrophysical targets and scenarios is mandatory should we aim for accurate predictions of dark matter-induced fluxes for investing significant telescope observing time on selected targets and for deriving robust conclusions from our dark matter search efforts. In this regard, a precise characterization of the statistical and structural properties of subhalos becomes critical. In this Special Issue, we aim to summarize where we stand today on our knowledge of the different aspects of the dark matter halo substructure; to identify what are the remaining big questions, and how we could address these; and, by doing so, to find new avenues for research.
Author: Alexander Victorovich Shirokov
Author: Alexander Victorovich Shirokov
Author: 
Author: 
Author: Warren Richard Morningstar
Author: Siegfried Wagner
Author: Carlos Chover Lopez
Author: Shaun Cole
Author: Reuben David Blaff
Author: Miguel A. Sánchez-Conde
Author: Massimo Persic