We use the positions and velocities of satellites of our galaxy and of other spiral galaxies to determine the radial mass profile of dark matter halos. We combine our measurement of the velocities of five remote Galactic satellites with published observations of the other Galactic satellites to obtain a complete sample of test particles. We then apply statistical techniques and timing arguments to deduce that the mass of the Galaxy is ≳ 1.3 x 10¹²M(⊙) for standard assumptions and that the halo extends beyond 100 kpc Galactocentric distance. We confirm our result by examining the dynamics of other Local Group galaxies. Subsequently, we expand our study to include nearby (1000 km s⁻¹ < ν(R) < 7000 km s⁻¹) Sb-Sc type galaxies. We use multiaperture spectrometers to conduct a survey for satellite galaxies and are able to double the sample of known satellite galaxies (satellites are defined to be at least eight times fainter than the primary) of isolated unbarred late-type spirals. The homogeneity of the primaries allows us to combine observations of satellites of various primaries and analyze the dynamical properties of the ensemble. The characteristics of this satellite sample (number, radial and azimuthal distribution, luminosity function, orbital characteristics, and contamination) are discussed. Finally, new models of the dynamics of satellite galaxies are developed that include the effects of the cosmological evolution of the halos and do not presume that halos are virialized. These models are used to constrain the mass distribution in which the satellite galaxies orbit. We conclude that only model halos with more than 10¹²M(⊙) within a galactocentric radius of 200 kpc are acceptable (90% confidence limit) for orbits of eccentricity < 0.9. The preferred models (60% confidence limit) are of halos with more than 1.6 x 10¹²M(⊙) within 200 kpc. Halos that formed in a universe with Ω = 1 also fall within the preferred range and have ∼ 3 x 10¹²M(⊙) within 200 kpc. In addition, we infer that the satellites’ orbital eccentricities are typically less than 0.9. These results, in conjunction with the results obtained for the halo of our galaxy, constitute convincing evidence for the existence of large (>200 kpc) and massive (> 10¹²M(⊙), M/L > 80) dark matter halos around isolated unbarred late-type spiral galaxies.

Cheng, Dalong = 衰變暗物質模型下的宇宙結構演化 / 程大龍. / Thesis Ph.D. Chinese University of Hong Kong 2014. / Includes bibliographical references (leaves 105-115). / Abstracts also in Chinese. / Title from PDF title page (viewed on 26, October, 2016). / Cheng, Dalong = Shuai bian an wu zhi mo xing xia de yu zhou jie gou yan hua / Cheng Dalong.

published_or_final_version / Physics / Master / Master of Philosophy

Thesis (Ph.D.)--University of Melbourne, School of Physics, 2005. / Typescript (photocopy). Includes bibliographical references (leaves [171]-185).

Thesis (M.Sc.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2008/12/07). Includes bibliographical references.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Howard Baer, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Jan. 27, 2005). Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1993.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Paul R. Shapiro. Vita. Includes bibliographical references.

Hidden sector or dark sector states appear in many extensions to the Standard Model (SM), to provide particle mediators for dark matter in the universe or to explain astrophysical observations such as the positron excess in the cosmic microwave background radiation flux. A hidden or dark sector can be introduced with an additional U(1)d dark gauge symmetry. The discovery of the Higgs boson in 2012 during Run 1 by the Large Hadron Collider (ATLAS and CMS) opens a new and rich experimental program for Beyond Standard Model physics (BSM) based on the Higgs Portal. This exotic discovery route uses couplings to the dark sector at the Higgs level, which were not experimentally accessible before. This thesis presents the searches of possible exotic decays: H → ZdZ(d) → 4` where Zd is a dark vector boson. It had been initiated in the Run 1 period of the LHC using the ATLAS detector at CERN. The results showed (tantalizingly) two signal events where none were expected, so that in the strict criteria of High Energy Physics, the result was not yet statistically significant. The Run 1 analysis for a 8 TeV collision energy is further developed in Run 2 with a 13 TeV collision energy, to expand the search area, take advantage of higher statistics, a higher Higgs production cross section, and substantially better performance of the ATLAS detector. In this work, the search is further broadened and includes allowing the mass of the originating boson (the dark Higgs S) to vary from the SM value. This allows the search for the dark vector boson to also explore higher or lighter masses than the SM Higgs boson. This extended search is efficient and could include a more general class of models, with the mass constraint of the SM Higgs portal lifted. This thesis reviews the analysis results from Run 1 and Run 2, and presents its iteration in the full Run 2 search by focusing on its new channel where the additional scalar S (with mS 6= mH) decays to 4` via two dark vector boson states Zd . The case where the Higgs decays to 4` via two Zd (H → ZdZd → 4`) and also called high mass channel, has been just unblinded. Nineteen data events are observed where 14 were predicted. In overall, the data are consistent with the Monte Carlo prediction. No evidence of deviation from the Standard Model expectations are observed. / College of Engineering, Science and Technology / Ph. D. (Physics)

暗物質乃構成宇宙的主要部分。而暗物質，即自身為不可見之物，無論自我湮滅與否，皆可能於各方面影響天體的特性。 / 在本論文中，我們首先研究一個混入非自我湮滅費米子暗物質的核心，並藉二流體方法，探討它如何影響中子星的靜態平衡結構。我們發現若達到足夠大的暗物質質量比重時，便可產生一種新型的致密星一顆由暗物質支配、半徑有數公里的中子星。然後，我們研究該核心導致中子星的線性變化，並應用此星體模型解釋已觀測的特細中子星，也考察此暗物質對中子星的冷卻過程的影響，和不同粒子質量的暗物質的效果。最後，我們討論該核心的徑向震動，從中發現新一種震動模式。 / 接下來，我們集中討論混入暗物質的核心如何干涉主序星的星體演化。一般而言，此核心皆縮短主序星的壽命，並改變演化間唯量，譬如氫融合及氦融合的最低所需質量。但就一個擁有可觀質量的暗物質核心而言，我們發現幾種唯象的改變包括主序星壽命的延長，高質量恆星的橫向分支的消失，以及星體演化的新路徑。由此我們得出，把暗物質放入考慮之列，能令星體演化的討論變得更有系統，也是不可或缺的。再者，我們論證前述的星體，即由暗物質支配的中子星，亦可能從類近的演化中產生。 / 最後，我們轉向研究，在牛頓水動力學中的球體對稱情況下，一個點質量的暗物質核心如何改變白矮星徑向運動的特性。於可行的模擬運算下，此核心的額外引力只局部改變星體的特性，如初始靜態平衡下的密度分佈的外型，而星體的徑向震動模式及震動頻率則不受影響。 / Dark matter constitutes a large proportion of matter in the universe and it is believed that dark matter, self-annihilating or not, can bring observational change to astrophysical objects in different aspects, even though it cannot be observed directly. / In chapter 2, we first study the effect of an admixed dark matter core, consisted of non-self-annihilating fermionic dark matter particles, to the equi-librium structure of a neutron star using the two-fluid formalism. We find that a new subclass of compact star, dark matter dominated neutron star, is formed for a sufficiently large mass fraction of dark matter, which has only a few-kilometer-sized visible radius. Also, we study the linear response of a neutron star towards a dark matter core; we apply the model to explain several observed neutron stars with extraordinary small radii and we study how the dark matter core affects the cooling properties of neutron stars. We examine the effects caused by the choice of dark matter particle mass. Then, we study the radial oscillation modes of a dark matter admixed neutron star, in which a new class of modes is present due to the admixture of dark matter. At last, we extend our study from neutron stars to strange stars, in which we discover that the response of a strange star to the presence of an admixed dark matter core is qualitatively different from a neutron star. / In chapter 3 we focus on the effect of the dark matter core to the stellar evolution of main-sequence stars. We find that in general the existence of a dark matter core reduces the stellar lifetime and quantitative change in the stellar evolution, such as the decrement of the threshold mass for hydro¬gen and helium fusion. But for sufficiently massive dark matter core, several qualitative changes are observed: they include an extension in main-sequence lifetime, absence of horizontal branch for high-mass stars and some new paths in the stellar evolution. From the study we find that the consideration of dark matter is indispensable in a systematic discussion of stellar evolution. Also we argue that dark matter dominated neutron star can be formed following similar stellar evolution processes. / In chapter 4 we turn to the impact of a point-mass dark matter core on the radial oscillation of a white dwarf by doing Newtonian hydrodynamical simulations in spherically symmetric scenarios. We find that, within feasible simulations, the effects of an extra gravity from the dark matter core is highly local. It creates a change in the initial static equilibrium density profile, but its radial oscillation patterns and oscillation frequencies remain unchanged. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Leung, Shing Chi = 非自我湮滅暗物質對致密星及主序星的影響 / 梁成志. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 119-131). / Abstracts also in Chinese. / Leung, Shing Chi = Fei zi wo yan mie an wu zhi dui zhi mi xing ji zhu xu xing de ying xiang / Liang Chengzhi. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Dark Matter: The mysterious piece in the Universe --- p.1 / Chapter 1.1.1 --- The puzzle of missing mass --- p.1 / Chapter 1.1.2 --- Dark Matter in Particle Physics --- p.2 / Chapter 1.1.3 --- Alternatives to Dark Matter --- p.4 / Chapter 1.2 --- Probing the Nature of Dark Matter --- p.5 / Chapter 1.3 --- Neutron Star Astrophysics --- p.8 / Chapter 1.3.1 --- Equilibrium Structure and Radial Oscillation Modes --- p.8 / Chapter 1.3.2 --- Non-radial Oscillation Modes --- p.9 / Chapter 1.3.3 --- Use of NS as a DM probe --- p.10 / Chapter 1.3.4 --- Rotating Neutron Stars --- p.11 / Chapter 1.4 --- Hydrodynamical Simulation --- p.12 / Chapter 1.4.1 --- Algorithm --- p.12 / Chapter 1.4.2 --- Applications in Astrophysics --- p.14 / Chapter 1.5 --- Structure of the thesis --- p.15 / Chapter 2 --- Astrophysical Properties of DANS --- p.17 / Chapter 2.1 --- Formalism --- p.17 / Chapter 2.1.1 --- Static Equilibrium Structure of DANS --- p.17 / Chapter 2.1.2 --- Choice of EOS --- p.19 / Chapter 2.1.3 --- Moment of inertia --- p.20 / Chapter 2.1.4 --- Equations for radial oscillations --- p.21 / Chapter 2.1.5 --- Equations for NS cooling --- p.23 / Chapter 2.1.6 --- EOS for strange quark matter --- p.32 / Chapter 2.2 --- Static Equilibrium Properties of DANS --- p.35 / Chapter 2.2.1 --- General Properties of DANS --- p.35 / Chapter 2.2.2 --- Linear Response of DANS --- p.39 / Chapter 2.2.3 --- Effects of DM particle mass --- p.41 / Chapter 2.3 --- Radial Oscillations of DANS --- p.44 / Chapter 2.3.1 --- One-fluid limit --- p.44 / Chapter 2.3.2 --- Oscillation modes of DANS --- p.45 / Chapter 2.3.3 --- Effects of DM particle mass --- p.51 / Chapter 2.4 --- Neutron Star Cooling --- p.52 / Chapter 2.4.1 --- Introduction --- p.52 / Chapter 2.4.2 --- Numerical Result in Neutrino Emission --- p.53 / Chapter 2.4.3 --- Time-dependent calculation --- p.54 / Chapter 2.4.4 --- Discussion --- p.58 / Chapter 2.5 --- Strange Star --- p.59 / Chapter 2.5.1 --- Introduction --- p.59 / Chapter 2.5.2 --- Strange Star Properties --- p.60 / Chapter 2.5.3 --- Discussion --- p.63 / Chapter 2.6 --- Chapter Summary --- p.65 / Chapter 3 --- Effects of Non-self-annihilating Dark Matter on Stellar Evolution --- p.66 / Chapter 3.1 --- Formulation --- p.66 / Chapter 3.1.1 --- Effect of Dark Matter --- p.66 / Chapter 3.1.2 --- Convergence test --- p.67 / Chapter 3.2 --- Results --- p.72 / Chapter 3.2.1 --- High mass stars --- p.74 / Chapter 3.2.2 --- Intermediate mass stars --- p.76 / Chapter 3.2.3 --- Low mass stars --- p.79 / Chapter 3.2.4 --- Brown Dwarfs --- p.82 / Chapter 3.3 --- Discussion --- p.85 / Chapter 3.3.1 --- Absence of Horizontal Branch --- p.85 / Chapter 3.3.2 --- Extended Main-sequence Lifetime --- p.87 / Chapter 3.3.3 --- Lower Mass Thresholds for Hydrogen Fusion and Helium Fusion --- p.88 / Chapter 3.3.4 --- New Stellar Evolution Path --- p.90 / Chapter 3.4 --- Chapter Summary --- p.91 / Chapter 4 --- Dynamical Simulation of Hybrid White Dwarf --- p.93 / Chapter 4.1 --- Formalism --- p.93 / Chapter 4.2 --- Convergence Test --- p.94 / Chapter 4.3 --- Numerical Results --- p.96 / Chapter 4.4 --- Chapter summary --- p.98 / Chapter 5 --- Conclusion --- p.101 / Chapter A --- DANS as an Alternative to Strange Stars --- p.105 / Chapter B --- Verification of separated TOV equations --- p.107 / Chapter C --- Code for numerical evolution --- p.109 / Chapter D --- Notation Convention and Units --- p.111 / Chapter E --- Discussion on the smearing of DM core --- p.113 / Chapter F --- Unit conversion --- p.118 / Bibliography --- p.119