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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.
1

Dark Matter: Origin, Detection, and Collider Implications

Dolle, Ethan Michael January 2009 (has links)
Cosmological observations have precisely measured the amount of cold dark matter (CDM) in the Universe. The best fit value corresponds to around 23% of the Universe being composed of CDM. Nothing in the Standard Model (SM) is able to account for this cold dark matter. This provides unambiguous evidence for physics beyond the SM. From particle physics, the hierarchy between the electroweak and Planck scales within the SM provides motivation to consider new physics beyond the SM. In this thesis, I investigated the origin of CDM, analyzed various prospects for indirect detection, and studied its collider implications.We focused on two such models: the Left Right Twin Higgs (LRTH) model and the Inert Doublet model (IDM). Both of these models contain a neutral scalar that is stable and a good CDM candidate. We performed a CDM analysis, and identified regions of parameter space that can account for all of the CDM in the Universe.CDM can become trapped around massive objects such as the Sun, Earth, and galactic center. Over time, these CDM particles can annihilate to produce neutrinos and photons. Within the IDM framework, we analyzed the neutrino signal from the Sun and Earth and the photon signal from the galactic center.Due to the nature of new particles within the IDM, there are implications for signals at high energy colliders, such as the Large Hadron Collider (LHC). These particles are produced and can subsequently decay to CDM, jets, and leptons. Within the framework of the IDM, we performed a dilepton signal analysis at the LHC.There exists a synergy between particle physics and cosmology. The study of the interplay between these two fields could provide valuable insights and bring a better understanding of Nature within our grasp. It is an exciting time for physics.
2

Radon Background Reduction in DEAP-1 and DEAP-3600

O'DWYER, EOIN 10 January 2011 (has links)
The Dark Matter Experiment with Liquid Argon Using Pulse Shape Discrim- ination (DEAP) is a dark matter experiment based in the SNOLAB facility in Sudbury, Ontario. Its aim is to detect WIMPs, Weakly Interacting Massive Par- ticles, that may make up the missing component of the matter in our universe by the scintillation of liquid argon from nuclear recoils. A 7 kg prototype, DEAP-1, is currently in operation with work underway to scale up to a 1 tonne detector, DEAP-3600, by 2012. For DEAP-3600 to be a competitive dark matter search, a limit of 0.2 fiducial surface alpha events is required in the energy region of interest for three years of run time, or 150 total surface events. Of particular concern to the DEAP experiment is 222Rn and its daughter prod- ucts, as the alpha decays of these isotopes may create events in the detector that mimic a WIMP signature. The first half of this thesis concerns the testing and suc- cessful use of an activated carbon trap to eliminate 222Rn from the argon gas source in DEAP-1. The Carbo-Act F2/F3 grain activated carbon brand was tested as a potential ultra-low activity candidate for a DEAP-3600 filtration system and was found to have an upper limit for its 222Rn emanation rate of 284 atoms/day/kg. A temperature swing system is proposed. If operated at 110 K, an upper limit of five atoms of 222Rn can be expected to enter the detector from the trap. An indirect relationship between the number of low energy nuclear recoil events in the DEAP WIMP region of interest and the number of radon alpha decays was found. The ratio between the low energy events in the WIMP region of interest and the high energy alphas was found to be 0.18 ± 0.03 in the detector. From this, the upper limit of the contribution from the proposed radon trap to the WIMP background in DEAP-3600 will be be ten events for three years of run time, which is within acceptable limits. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-01-10 10:27:19.303
3

Abundance Matching with the Galaxies of the Virgo Cluster and the Stellar-to-Halo Mass Relation

Grossauer, Jonathan January 2012 (has links)
Using data from the Next Generation Virgo Cluster Survey and high-resolution simulations of Virgo cluster-like halos, we determine the stellar-to-halo mass relation (SHMR) for subhalos, using the technique of abundance matching. The subhalo SHMR differs markedly from its field galaxy counterpart, regardless of how the subhalo mass is defined (mass at z = 0, mass at infall, or maximum mass while in the field). The slope of the relation at low mass (M⋆<10^10 Msun) is in all cases steeper than the same for the field. We find conflicting indicators of whether this difference in slope indicates an increasing or decreasing dark-to-stellar ratio; further modelling is required to reach a definitive conclusion. We also find evidence for the existence of a measurable age gradient in velocity, such that older subhalos have lower velocities than their younger peers. This opens the possibility that good quality redshifts of the lower mass galaxies of the Virgo cluster might provide additional constraints on the SHMR at high redshift and its evolution. Finally, we investigate the degree to which mergers, particularly major mergers, cause mixing of old and new material in halos, which has implications for the robustness of any implied radial age gradient. We find only a slight increase in mixing for major mergers over minor mergers, and little evidence for any large amount of mixing being induced by mergers of any ratio.
4

Abundance Matching with the Galaxies of the Virgo Cluster and the Stellar-to-Halo Mass Relation

Grossauer, Jonathan January 2012 (has links)
Using data from the Next Generation Virgo Cluster Survey and high-resolution simulations of Virgo cluster-like halos, we determine the stellar-to-halo mass relation (SHMR) for subhalos, using the technique of abundance matching. The subhalo SHMR differs markedly from its field galaxy counterpart, regardless of how the subhalo mass is defined (mass at z = 0, mass at infall, or maximum mass while in the field). The slope of the relation at low mass (M⋆<10^10 Msun) is in all cases steeper than the same for the field. We find conflicting indicators of whether this difference in slope indicates an increasing or decreasing dark-to-stellar ratio; further modelling is required to reach a definitive conclusion. We also find evidence for the existence of a measurable age gradient in velocity, such that older subhalos have lower velocities than their younger peers. This opens the possibility that good quality redshifts of the lower mass galaxies of the Virgo cluster might provide additional constraints on the SHMR at high redshift and its evolution. Finally, we investigate the degree to which mergers, particularly major mergers, cause mixing of old and new material in halos, which has implications for the robustness of any implied radial age gradient. We find only a slight increase in mixing for major mergers over minor mergers, and little evidence for any large amount of mixing being induced by mergers of any ratio.
5

The dynamics of satellite galaxies.

Zaritsky, Dennis Fabian. January 1991 (has links)
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.
6

Neutrino Signals from Dark Matter

Erkoca, Arif Emre January 2010 (has links)
Large-scale neutrino telescopes will be powerful tools to observe multitude of mysterious phenomena happening in the Universe. The dark matter puzzle is listed as one of them. In this study, indirect detection of dark matter via neutrino signals is presented. The upward muon, the contained muon and the hadronic shower fluxes are calculated, assuming annihilation/decay of the dark matter in the core of the astrophysical objects and in the Galactic center. Direct neutrino production and secondary neutrino production from the decay of Standard Model particles produced in the annihilation/decay of dark matter are studied. The results are contrasted to the ones previously obtained in the literature, illustrating the importance of properly treating muon propagation and energy loss for the upward muon flux. The dependence of the dark matter signals on the density profile, the dark matter mass and the detector threshold are discussed. Different dark matter models (gravitino, Kaluza-Klein and leptophilic) which can account for recent observations of some indirect searches are analyzed regarding their detection in the kilometer size neutrino detectors in the near future. Muon and shower rates and the minimum observation times in order to reach 2σ detection significance are evaluated, with the result suggesting that the optimum cone half angles chosen about the Galactic center are about 10° (50°) for the muon (shower) events. A detailed analysis shows that for the annihilating dark matter models such as the leptophilic and Kaluza-Klein models, upward and contained muon as well as showers yield promising signals for dark matter detection in just a few years of observation, whereas for decaying dark matter models, the same observation times can only be reached with showers. The analytical results for the final fluxes are also obtained as well as parametric forms for the muon and shower fluxes for the dark matter models considered in this study.
7

Gravitational microlensing of extended objects

Coleman, Iain James January 1998 (has links)
No description available.
8

Cosmological structure formation in decaying dark matter models / 衰變暗物質模型下的宇宙結構演化 / CUHK electronic theses & dissertations collection / Cosmological structure formation in decaying dark matter models / Shuai bian an wu zhi mo xing xia de yu zhou jie gou yan hua

January 2014 (has links)
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.
9

Studies of dark matter in and around stars

Sivertsson, Sofia January 2012 (has links)
There is by now compelling evidence that most of the matter in the Universe is in the form of dark matter, a form of matter quite different from the matter we experience in every day life. The gravitational effects of this dark matter have been observed in many different ways but its true nature is still unknown. In most models, dark matter particles can annihilate with each other into standard model particles; the direct or indirect observation of such annihilation products could give important clues for the dark matter puzzle. For signals from dark matter annihilations to be detectable, typically high dark matter densities are required. Massive objects, such as stars, can increase the local dark matter density both via scattering off nucleons and by pulling in dark matter gravitationally as a star forms. Annihilations within this kind of dark matter population gravitationally bound to a star, like the Sun, give rise to a gamma ray flux. For a star which has a planetary system, dark matter can become gravitationally bound also through gravitational interactions with the planets. The interplay between the different dark matter populations in the solar system is analyzed, shedding new light on dark matter annihilations inside celestial bodies and improving the predicted experimental reach. Dark matter annihilations inside a star would also deposit energy in the star which, if abundant enough, could alter the stellar evolution. This is investigated for the very first stars in the Universe. Finally, there is a possibility for abundant small scale dark matter overdensities to have formed in the early Universe. Prospects of detecting gamma rays from such minihalos, which have survived until the present day, are discussed. / Kosmologiska observationer har visat att större delen av materian i universum består av mörk materia, en form av materia med helt andra egenskaper än den vi upplever i vardagslivet. Effekterna av denna mörka materia har observerats gravitationellt på många olika sätt men vad den egentligen består av är fortfarande okänt. I de flesta modeller kan mörk materia-partiklar annihilera med varandra till standardmodellpartiklar. Att direkt eller indirekt observera sådana annihilationsprodukter kan ge viktiga ledtrådar om vad den mörka materian består av. För att kunna detektera sådana signaler fordras typiskt höga densiteter av mörk materia. Stjärnor kan lokalt öka densiteten av mörk materia, både via spridning mot atomkärnor i stjärnan och genom den ökande gravitationskraften i samband med att en stjärna föds. Annihilationer inom en sådan mörk materia-population gravitationellt bunden till en stjärna, till exempel solen, ger upphov till ett flöde av gammastrålning, som beräknas. För en stjärna som har ett planetsystem kan mörk materia även bli infångad genom gravitationell växelverkan med planeterna. Samspelet mellan de två mörk materia-populationerna i solsystemet analyseras, vilket ger nya insikter om mörk materia-annihilationer inuti himlakroppar och förbättrar de experimentella möjligheterna att detektera dem. Mörk materia-annihilationer inuti en stjärna utgör också en extra energikälla för stjärnan, vilket kan påverka stjärnans utveckling om mörk materia-densiteten blir tillräckligt stor. Denna effekt undersöks för de allra första stjärnorna i universum. Slutligen finns det också en möjlighet att det i det tidiga universum skapades mörk materia-ansamlingar som fortfarande finns kvar idag. Utsikterna att upptäcka dessa genom mätning av gammastrålning diskuteras. / QC 20120130
10

Observing dark in the galactic spectrum?

Lawson, Kyle 05 1900 (has links)
Observations from a broad range of astrophysical scales have forced us to the realization that the well understood matter comprising the stars and galaxies we see around us accounts for only a small fraction of the total mass of the Universe. An amount roughly five times larger exist in the form of dark matter about which we have virtually no direct evidence apart from its large scale gravitational effects. It is also known that the largest contribution to the energy density of the universe is the dark energy, a negative pressure form of energy which will not be dealt with here. I will present a candidate for the dark matter which is based completely in known physics and which presents several possible observational signatures. In this model the dark matter is composed of dense nuggets of baryonic matter and antimatter in a colour superconducting state. If these object are sufficiently massive their low number density will make them effectively dark in the sense that collisions with visible matter become infrequent. This work presents the basics of dark matter as a colour superconductor and then uses the physical properties of the quark nuggets to extract observational consequences.

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