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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Supersymmetric Dark Matter : aspects of sfermion coannihilations

Schelke, Mia January 2004 (has links)
<p>There is very strong evidence that ordinary matter in the Universe is outweighed by almost ten times as much so-called dark matter. Dark matter does neither emit nor absorb light and we do not know what it is. One of the theoretically favoured candidates is a so-called neutralino from the supersymmetric extension of the Standard Model of particle physics.</p><p>A theoretical calculation of the expected cosmic neutralino density must include the so-called coannihilations. Coannihilations are particle processes in the early Universe with any two supersymmetric particles in the initial state and any two Standard Model particles in the final state. In this thesis we discuss the importance of these processes for the calculation of the relic density. We will go through some details in the calculation of coannihilations with one or two so-called sfermions in the initial state. This includes a discussion of Feynman diagrams with clashing arrows, a calculation of colour factors and a discussion of ghosts in non-Abelian field theory. </p><p>Supersymmetric models contain a large number of free parameters on which the masses and couplings depend. The requirement, that the predicted density of cosmic neutralinos must agree with the density observed for the unknown dark matter, will constrain the parameters. Other constraints come from experiments which are not related to cosmology. For instance, the supersymmetric loop contribution to the rare <i>b</i> -><i> sγ</i> decay should agree with the measured branching fraction. The principles of the calculation of the rare decay are discussed in this thesis. Also on-going and planned searches for cosmic neutralinos can constrain the parameters. In one of the accompanying papers in the thesis we compare the detection prospects for several current and future searches for neutralino dark matter. </p>
32

The implications of a live halo for galactic warps and satellite dynamics

Jiang, Ing-Guey January 1999 (has links)
No description available.
33

Particle detection with superconducting phonon sensors

Hahn, Andreas January 1994 (has links)
No description available.
34

Results from the ZEPLIN-III experiment

Hollingsworth, Anthony January 2013 (has links)
The majority of matter in the Universe is dark. World wide efforts to understand this dark component of the Universe are underway and the current evidence suggests the existence of a non-relativistic, non-baryonic and weakly interacting massive particle (WIMP). This weakly interacting dark matter should occasionally couple to baryonic matter, primarily through nuclear interactions. The predicted event rates are low (< O(1) events/kg/day). The energy deposited is also expected to be low (<~ 50 keV), and so distinguishing a WIMP signal above the radioactive and cosmic backgrounds is a difficult challenge. The ZEPLIN{III device was designed to meet this challenge and achieve a competitive sensitivity to WIMP-nucleon interactions. The ZEPLIN{III detector is a two phase time projection chamber using liquid xenon as a target. The instrument was designed to detect dark matter by measuring scintillation and ionisation. Measuring two signals produced by incident radiation allows for discrimination between event types. This allows separation of the main component of the background radiation (primarily electron recoils) from any population of WIMP events that may be present in the data. The ZEPLIN-III detector completed its first science run in 2008, achieving a discrimination power of 1:7800 between nuclear and electron recoils, the highest of any liquid xenon detector. This result limited the WIMP-nucleon cross section to less than 8:4 X 10-8 pb at 90% confidence level (double sided) for a WIMP mass of 55 GeV/c2. The ZEPLIN-III detector then entered an upgrade phase. The two main improvements included the installation of a new ultra-low background PMT array, significantly reducing the main source of background events, and the addition of a veto detector. The veto detector significantly increased the detector's ability to reject WIMP-like background signals, which may be produced by background neutron events. The veto detector also aided background discrimination by detecting 28% of γ-ray events from the fiducial volume of ZEPLIN-III. The second science run of ZEPLIN-III began in June 2010 and continued until May 2011. During the second science run the discrimination power was 1:280 between nuclear and electron recoils. A total of 8 events were observed in the WIMP search region, which is consistent with background expectations. Assuming a null detection allowed the exclusion of the scalar cross-section above 4:8 10-8 pb near a WIMP mass of 51 GeV/c2. This result was combined with the result from a re-analysis of the first science run using more recent results for the relative scintillation yield, Leff, to give a total limit on the spin independent cross-section of 3:9 X 10-8 pb at 90% confidence near 52 GeV/c2 WIMP mass for the ZEPLIN-III experiment. The WIMP-neutron spin-dependent cross-section limit is 8:0 X 10-3 pb at 50 GeV/c2 at 90% confidence for the combined first and second science runs. At the time of publication, these were the world's second best, and best results, respectively.
35

DETECTION OF LENSING SUBSTRUCTURE USING ALMA OBSERVATIONS OF THE DUSTY GALAXY SDP.81

Hezaveh, Yashar D., Dalal, Neal, Marrone, Daniel P., Mao, Yao-Yuan, Morningstar, Warren, Wen, Di, Blandford, Roger D., Carlstrom, John E., Fassnacht, Christopher D., Holder, Gilbert P., Kemball, Athol, Marshall, Philip J., Murray, Norman, Levasseur, Laurence Perreault, Vieira, Joaquin D., Wechsler, Risa H. 19 May 2016 (has links)
We study the abundance of substructure in the matter density near galaxies using ALMA Science Verification observations of the strong lensing system SDP. 81. We present a method to measure the abundance of subhalos around galaxies using interferometric observations of gravitational lenses. Using simulated ALMA observations we explore the effects of various systematics, including antenna phase errors and source priors, and show how such errors may be measured or marginalized. We apply our formalism to ALMA observations of SDP. 81. We find evidence for the presence of a M = 10(8.96 +/- 0.12)M(circle dot) subhalo near one of the images, with a significance of 6.9 sigma in a joint fit to data from bands 6 and 7; the effect of the subhalo is also detected in both bands individually. We also derive constraints on the abundance of dark matter (DM) subhalos down to M similar to 2 x 10(7) M-circle dot, pushing down to the mass regime of the smallest detected satellites in the Local Group, where there are significant discrepancies between the observed population of luminous galaxies and predicted DM subhalos. We find hints of additional substructure, warranting further study using the full SDP. 81 data set (including, for example, the spectroscopic imaging of the lensed carbon monoxide emission). We compare the results of this search to the predictions of Lambda CDM halos, and find that given current uncertainties in the host halo properties of SDP. 81, our measurements of substructure are consistent with theoretical expectations. Observations of larger samples of gravitational lenses with ALMA should be able to improve the constraints on the abundance of galactic substructure.
36

Effects of non-self-annihilating dark matter on compact stars and main-sequence stars. / 非自我湮滅暗物質對致密星及主序星的影響 / Effects of non-self-annihilating dark matter on compact stars and main-sequence stars. / Fei zi wo yan mie an wu zhi dui zhi mi xing ji zhu xu xing de ying xiang

January 2012 (has links)
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
37

Supersymmetric Dark Matter : aspects of sfermion coannihilations

Schelke, Mia January 2004 (has links)
There is very strong evidence that ordinary matter in the Universe is outweighed by almost ten times as much so-called dark matter. Dark matter does neither emit nor absorb light and we do not know what it is. One of the theoretically favoured candidates is a so-called neutralino from the supersymmetric extension of the Standard Model of particle physics. A theoretical calculation of the expected cosmic neutralino density must include the so-called coannihilations. Coannihilations are particle processes in the early Universe with any two supersymmetric particles in the initial state and any two Standard Model particles in the final state. In this thesis we discuss the importance of these processes for the calculation of the relic density. We will go through some details in the calculation of coannihilations with one or two so-called sfermions in the initial state. This includes a discussion of Feynman diagrams with clashing arrows, a calculation of colour factors and a discussion of ghosts in non-Abelian field theory. Supersymmetric models contain a large number of free parameters on which the masses and couplings depend. The requirement, that the predicted density of cosmic neutralinos must agree with the density observed for the unknown dark matter, will constrain the parameters. Other constraints come from experiments which are not related to cosmology. For instance, the supersymmetric loop contribution to the rare b -&gt; sγ decay should agree with the measured branching fraction. The principles of the calculation of the rare decay are discussed in this thesis. Also on-going and planned searches for cosmic neutralinos can constrain the parameters. In one of the accompanying papers in the thesis we compare the detection prospects for several current and future searches for neutralino dark matter.
38

Local Group Analogues

Speller, Ryan January 2012 (has links)
The abundance of satellite galaxies is a critical small-scale test of the standard cosmological model. From comparing the predictions of structure formation in simulations with observations of Local Group dwarf galaxies there is a clear mismatch in the abundance, leading to the so-called “missing satellites” problem. The comparison between simulation and observation have, however, suffered from a limited sample of satellite galaxies, with the only reasonably complete sample being from the most local galaxy groups. It is unknown whether the observed abundance of dwarf satellite galaxies of the nearest groups is statistically representative of the abundance of dwarf satellites in the greater universe. We construct a volume-limited sample of galaxies down to a well-defined stellar mass limit (M★ ≥ 6 × 109 Msun ) using the Atlas3D parent sample of spiral and ellipsoidal galaxies by Cappellari et al. 2011. In order to statistically identify bound satellites around galaxies in our primary catalogue, we apply cuts on the background based on the properties of known dwarf satellites of the Local Group using both the Sloan Digital Sky Survey Data Release 8 (SDSS DR8) (http://www.sdss3.org/dr8/) spectroscopic and photometric galaxy catalogues. We detect an over-density of faint objects at projected separations of < 500 kpc at S/N ∼ 8, corresponding to an average of 4.8 ± 0.65 satellite detections per primary after stacking these systems and subtracting the background. We further find that the over-density of faint objects strongly depends on primary morphology and magnitude. While the Milky Way seems to be unusual in its number of bright satellites, our faint end satellite abundances are in agreement from the ∆m luminosity function for primaries in our sample as bright as the Milky Way. Our work has extended the work of previous authors by several magnitudes further down the faint end of the luminosity function.
39

Cosmological simulations of dark matter halos /

Reed, Darren S. January 2003 (has links)
Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 201-212).
40

The nature and consequences of cosmological halo formation: dark matter and the dark ages

Ahn, Kyungjin 28 August 2008 (has links)
Not available / text

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