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Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The decay of very heavy metastable relics of the Early Universe can produce ultra-high energy cosmic rays (UHECRs) in the halo of our own Galaxy. In this model, no Greisen-Zatsepin-Kuzmin cutoff is expected because of the short propagation distances. They show here that, as a consequence of the hierarchical build up of the halo, this scenario predicts the existence of small scale anisotropies in the arrival directions of UHECRs, in addition to a large scale anisotropy, known from previous studies. They also suggest some other observable consequences of this scenario which will be testable with upcoming experiments, as Auguer, EUSO and OWL.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The decay of very heavy metastable relics of the Early Universe can produce ultra-high energy cosmic rays (UHECRs) in the halo of our own Galaxy. In this model, no Greisen-Zatsepin-Kuzmin cutoff is expected because of the short propagation distances. They show here that, as a consequence of the hierarchical build up of the halo, this scenario predicts the existence of small scale anisotropies in the arrival directions of UHECRs, in addition to a large scale anisotropy, known from previous studies. They also suggest some other observable consequences of this scenario which will be testable with upcoming experiments, as Auguer, EUSO and OWL.
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: Karia Radh Dibert Publisher: ISBN: Category : Languages : en Pages : 40
Book Description
Self-interacting dark matter, which serves as an alternative to collisionless cold dark matter, may be useful for solving the small-scale galaxy formation problems present in the Lambda-Cold Dark Matter model. So far, most self-interacting dark matter simulations have considered only elastic collisions between particles. Using the results of a numerical implementation in the AREPO code, the effects of two-state inelastic dark matter on the density profiles, velocity dispersions, pseudo-phase-space density profiles, orbital anisotropy parameter profiles, and principal axis ratios of galactic halos are examined. We find that inelastic self-interacting dark matter halos differ from both cold dark matter halos and elastic self-interacting dark matter halos in density profiles, in velocity dispersion profiles, in pseudo-phase-space density profiles, and in orbital anisotropy parameter profiles, while the shapes of the halos generated by elastic and inelastic self-interacting dark matter models are relatively similar.
Author: Savvas Michael Koushiappas Publisher: ISBN: Category : Black holes (Astronomy) Languages : en Pages :
Book Description
Abstract: It is without doubt that in recent years cosmology has entered an era where cosmological parameters are now measured precisely enough to derive conclusions about the underlying characteristics of the Universe. I present an overview of the methods used to estimate the parameters that lead to the standard cosmological model. After a brief detour on the current understanding of the mechanisms that lead to galaxy formation, I present a model in which the seeds of supermassive black holes observed in galactic spheroids form out of the lowest angular momentum gas in proto-galaxies at high redshift. I assume that the gas in early-forming, rare-peak halos has a distribution of specific angular momentum similar to that derived for the dark matter. In halos more massive than a critical threshold, proto-galactic disks are gravitationally unstable and experience an efficient viscosity that transfers angular momentum outward allowing mass inflow. This process continues until the first massive stars disrupt the disk. The seed black holes created in this manner have a characteristic mass scale, roughly independent of the redshift of formation. By the redshift of reionization, the comoving mass density is comparable to that inferred from observations, with room for appropriate additional luminous growth during a later quasar accretion phase. The hierarchical merger process naturally leads to a linear correlation between black-hole mass and stellar spheroid mass. Quite orthogonal to this study, I estimate the probability of detecting gamma-rays from the annihilation of neutralino dark matter in the Milky Way substructure. I characterize substructure statistically based on Monte Carlo realizations of the formation of a Milky Way-like halo. I find that it may be possible for upcoming experiments to detect gamma-rays from dark matter substructure if the neutralino is relatively light, while for a heavy neutralino such a detection would be unlikely. I find that the probability of detection is sensitive to poorly-constrained input parameters, particularly those that characterize the primordial power spectrum. I conclude that the lack of a detected gamma-ray signal gives very little information about the supersymmetric parameter space due to uncertainties associated with both the properties of substructure and cosmological parameters.
Author: National Research Council Publisher: National Academies Press ISBN: 0309157994 Category : Science Languages : en Pages : 324
Book Description
Driven by discoveries, and enabled by leaps in technology and imagination, our understanding of the universe has changed dramatically during the course of the last few decades. The fields of astronomy and astrophysics are making new connections to physics, chemistry, biology, and computer science. Based on a broad and comprehensive survey of scientific opportunities, infrastructure, and organization in a national and international context, New Worlds, New Horizons in Astronomy and Astrophysics outlines a plan for ground- and space- based astronomy and astrophysics for the decade of the 2010's. Realizing these scientific opportunities is contingent upon maintaining and strengthening the foundations of the research enterprise including technological development, theory, computation and data handling, laboratory experiments, and human resources. New Worlds, New Horizons in Astronomy and Astrophysics proposes enhancing innovative but moderate-cost programs in space and on the ground that will enable the community to respond rapidly and flexibly to new scientific discoveries. The book recommends beginning construction on survey telescopes in space and on the ground to investigate the nature of dark energy, as well as the next generation of large ground-based giant optical telescopes and a new class of space-based gravitational observatory to observe the merging of distant black holes and precisely test theories of gravity. New Worlds, New Horizons in Astronomy and Astrophysics recommends a balanced and executable program that will support research surrounding the most profound questions about the cosmos. The discoveries ahead will facilitate the search for habitable planets, shed light on dark energy and dark matter, and aid our understanding of the history of the universe and how the earliest stars and galaxies formed. The book is a useful resource for agencies supporting the field of astronomy and astrophysics, the Congressional committees with jurisdiction over those agencies, the scientific community, and the public.
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Author: Miguel A. Sánchez-Conde
Author: Karia Radh Dibert
Author: Franco Giovannelli
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Author: Savvas Michael Koushiappas
Author: National Research Council
Author: Jun-Hwan Choi
Author: Masahiro Teshima
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