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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.
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.
If standard gravitational theory is correct, then most of the matter in the universe is in an unidentified form which does not emit enough light to have been detected by current instrumentation. This book is the second editon of the lectures given at the 4th Jerusalem Winter School for Theoretical Physics, with new material added. The lectures are devoted to the “missing matter” problem in the universe, the search to understand dark matter. The goal of this volume is to make current research work on unseen matter accessible to students without prior experience in this area and to provide insights for experts in related research fields. Due to the pedagogical nature of the original lectures and the intense discussions between the lecturers and the students, the written lectures included in this volume often contain techniques and explanations not found in more formal journal publications.
Eighty years after its initial discovery, the nature of dark matter remains a mystery. Contrary to observational evidence, simulations of dark matter halos predict cuspy density profiles and an abundant population of dwarf galaxies. Increasingly refined measurements of the dark matter halos in galaxies reveal a large variety of halo shapes and sizes, and so far no universal profile has been able to incorporate them all. Among the numerous dark matter candidates, models of so-called quantum cold dark matter (QCDM) have the unique potential to address the many disparities between theory and observation. QCDM postulates that dark matter is composed primarily of extraordinarily light (as small as m 10−24eV) bosonic particles. Such a small mass suggests a Compton wavelength on the order of parsecs, motivating the use of quantum mechanics on a galactic scale. Since dark matter by definition has no electromagnetic interaction, QCDM particles are bound to the lowest energy state of the galactic halo by a collectively-produced gravitational potential in the Schrodinger equation. Thus in the first approximation a QCDM halo has the properties of a Bose-Einstein condensate, and the entire halo can be described by a single wave function. In this dissertation, previous models of QCDM are reconsidered and compared to the most recent observational evidence. A comprehensive model for QCDM is then developed for a closed gravitational Schrödinger-Poisson system using the Hartree approximation. It is shown that the ground state solution to this system is well-approximated by an Einasto density prfi le with a shape parameter n 0:56, which is a smooth-cored distribution. The model is then expanded to include the influence of galactic baryonic matter distributions and the effects of a scattering potential, as well as excited and mixedstate dark matter halos. The addition of a black hole to the galactic potential is shown to produce a more concentrated halo with a cuspier core. The inclusion of a small-scale luminous matter distribution also concentrates the halo, while a largescale distribution di uses it; in either case the smooth core of the halo is preserved. The addition of a scattering term produces a rounder and more diffuse density prfile; adding a sufficiently large black hole in combination with this term results in an even cuspier profile than the black hole alone. As a result of these additions, the model can be applied to a much larger range of halo shapes and sizes. Including excited states expands this range even further. A comprehensive analysis of the theoretical framework is also presented, including a fully analytic power series solution to the gravitational Schrödinger-Poisson system. Finally, the Einasto density profile used as a fit for both simulated and observed dark matter halos is examined in depth, with emphasis on its signi cance to the models presented herein.
Flat cosmology with collisionless cold dark matter (CDM) and cosmological constant ([Lambda]CDM cosmology) may have some problems on small scales, even though it has been very successful on large scales. We study the effect of Self-Interacting Dark Matter (SIDM) hypothesis on the density profiles of halos. Collisionless CDM predicts cuspy density profiles toward the center, while observations of low mass galaxies prefer cored profiles. SIDM was proposed by Spergel & Steinhardt [161] as a possible solution to this cuspy profile problem on low-mass scales. On the other hand, observations and collisionless CDM agree on mass scales of galaxy clusters. It is also known that the SIDM hypothesis would contradict with X-ray and gravitational lensing observations of cluster of galaxies, if the cross section were too large. Our final goal is to find the range of SIDM scattering cross section models that are consistent with those astrophysical observations in two different mass scales. There are two theoretical approaches to compute the effect of self-interacting scattering -- Gravitational N-body simulation with Monte Carlo scattering and conducting fluid model; those two approaches, however, had not been confirmed to agree with each other. We first show that two methods are in reasonable agreement with each other for both isolated halos and for halos with realistic mass assembly history in an expanding [Lambda]CDM universe; the value of cross section necessary to have a maximally relaxed low-density core in [Lambda]CDM is in mutual agreement. We then develop a semianalytic model that predicts the time evolution of SIDM halo. Our semianalytic relaxation model enables us to understand how a SIDM halo would relax to a cored profile, and obtain an ensemble of SIDM halos from collisionless simulations with reasonable computational resources. We apply the semianalytic relaxation model to CDM halos, and compare the resulting statistical distribution of SIDM halos with astrophysical observations. We show that there exists a range of scattering cross sections that simultaneously solve the cuspy core problem on low-mass scales and satisfy the galaxy cluster observations. We also present that other potential conflicts between [Lambda]CDM and observations could be resolved in Part II and III.
This thesis explores the possibility of searching for new effects of dark matter that are linear in g, an approach that offers enormous advantages over conventional schemes, since the interaction constant g is very small, g“1. Further, the thesis employs an investigation of linear effects to derive new limits on certain interactions of dark matter with ordinary matter that improve on previous limits by up to 15 orders of magnitude. The first-ever limits on several other interactions are also derived. Astrophysical observations indicate that there is five times more dark matter—an ‘invisible’ form of matter, the identity and properties of which still remain shrouded in mystery—in the Universe than the ordinary ‘visible’ matter that makes up stars, planets, dust and interstellar gases. Conventional schemes for the direct detection of dark matter involve processes (such as collisions with, absorption by or inter-conversion with ordinary matter) that are either quartic (g4) or quadratic (g2) in an underlying interaction constant g.
It is generally believed that most of the matter in the universe is dark, i.e. cannot be detected from the light which it emits (or fails to emit). Its presence is inferred indirectly from the motions of astronomical objects, specifically stellar, galactic, and galaxy cluster/supercluster observations. It is also required in order to enable gravity to amplify the small fluctuations in the cosmic microwave background enough to form the large-scale structures that we see in the universe today. For each of the stellar, galactic, and galaxy cluster/supercluster observations the basic principle is that if we measure velocities in some region, then there has to be enough mass there for gravity to stop all the objects flying apart. Dark matter has important consequences for the evolution of the universe and the structure within it. According to general relativity, the universe must conform to one of three possible types: open, flat, or closed. The total amount of mass and energy in the universe determines which of the three possibilities applies to the universe. In the case of an open universe, the total mass and energy density (denoted by the Greek letter Ù) is less than unity. If the universe is closed, Ù is greater than unity. For the case where Ù is exactly equal to one the universe is "flat". This new book details leading-edge research from around the globe.