Yeung, Shek = 暗能量和暗物質模型課題 / 楊碩. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (p. 88-91). / Abstracts in English and Chinese. / Yeung, Shek = An neng liang he an wu zhi mo xing ke ti / Yang Shuo. / Chapter 1 --- Overview of Cosmology --- p.1 / Chapter 1.1 --- The Friedmann-Robertson-Walker Metric and the Friedmann Equations --- p.1 / Chapter 1.2 --- The Hubble constant and the Expansion of the Universe --- p.3 / Chapter 1.3 --- The Energy Contents in the Universe --- p.4 / Chapter 1.4 --- Cosmological Observations --- p.8 / Chapter 2 --- Review of CMB Physics --- p.13 / Chapter 2.1 --- The Anisotropy Spectrum --- p.13 / Chapter 2.2 --- The Boltzmann Equations and Einstein Field Equation --- p.15 / Chapter 2.3 --- Initial Conditions --- p.18 / Chapter 2.4 --- Inhomogeneities of Matters --- p.21 / Chapter 2.5 --- Inhomogeneities and Anisotropies of Photons --- p.23 / Chapter 2.5.1 --- Tightly Coupled Limit of the Boltzmann equations --- p.23 / Chapter 2.5.2 --- Diffusion Damping --- p.25 / Chapter 2.5.3 --- Free Streaming --- p.25 / Chapter 2.5.4 --- Cosmological Parameters --- p.26 / Chapter 3 --- Extra Dimension Model with Casimir Effect --- p.28 / Chapter 3.1 --- Introduction --- p.28 / Chapter 3.2 --- Extra Dimension Model --- p.29 / Chapter 3.3 --- The Casimir Effect --- p.34 / Chapter 3.4 --- Results and Conclusion --- p.40 / Chapter 4 --- Decaying Sterile Neutrino Model --- p.44 / Chapter 4.1 --- Introduction --- p.44 / Chapter 4.2 --- The Model --- p.46 / Chapter 4.3 --- Results and Conclusion --- p.61 / Chapter 5 --- Summary of the Thesis --- p.86 / Bibliography --- p.88

Wong, Ka Wing = 含有暗物質核心的白矮星的物理性質 / 黃家榮. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 81-86). / Abstracts in English and Chinese. / Wong, Ka Wing = Han you an wu zhi he xin de bai ai xing de wu li xing zhi / Huang Jiarong. / Abstract --- p.ii / Acknowledgement --- p.iv / List of Abbreviations --- p.v / List of Figures --- p.vi / Table of Contents --- p.xi / Chapter 0 --- Introduction --- p.1 / Chapter 1 --- White Dwarfs --- p.5 / Chapter 1.1 --- Introduction --- p.5 / Chapter 1.2 --- Observation --- p.6 / Chapter 1.3 --- Mass-Radius Relationship & Mass Limit --- p.9 / Chapter 1.4 --- Type Ia Supernovae --- p.14 / Chapter 2 --- Dark Matter --- p.16 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Observational Evidences --- p.17 / Chapter 2.3 --- Dark Matter Candidates and their Categorization --- p.21 / Chapter 3 --- Moon-sized White Dwarf with a Dark Matter Core --- p.26 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- Model --- p.29 / Chapter 3.3 --- Results --- p.32 / Chapter 3.3.1 --- Typical Density Profile --- p.32 / Chapter 3.3.2 --- M-R Curves --- p.33 / Chapter 3.3.3 --- Scaling in n --- p.35 / Chapter 3.3.4 --- BPS Equation of State --- p.40 / Chapter 3.4 --- Discussion --- p.41 / Chapter 4 --- Newtonian Hydrodynamic Simulation of a Spherically Symmetric Star --- p.44 / Chapter 4.1 --- Introduction --- p.44 / Chapter 4.2 --- WENO Scheme --- p.46 / Chapter 4.3 --- Runge-Kutta Time Discretization --- p.48 / Chapter 4.4 --- Fluid Dynamics without Gravity in One Dimension --- p.49 / Chapter 4.4.1 --- Riemann Problem Tests --- p.50 / Chapter 4.5 --- Spherically Symmetric Fluid Dynamics without Gravity --- p.54 / Chapter 4.5.1 --- Diffusion Problem --- p.55 / Chapter 4.6 --- Spherically Symmetric Star --- p.57 / Chapter 4.6.1 --- Radial Oscillation of a White Dwarf --- p.58 / Chapter 4.6.2 --- Radial Oscillation of a White Dwarf with a Point-Sized Dark Matter Core --- p.64 / Chapter 4.7 --- Discussion --- p.68 / Chapter 5 --- Newtonian Hydrodynamic Simulation of a Spherically Symmetric Two-Fluid Star --- p.69 / Chapter 5.1 --- Introduction --- p.69 / Chapter 5.2 --- Spherically Symmetric Two-Fluid Stars --- p.70 / Chapter 5.2.1 --- A White Dwarf with a Dark Matter Core --- p.71 / Chapter 5.3 --- Discussion --- p.77 / Chapter 6 --- Summary --- p.79 / Bibliography --- p.81

The focus of this thesis is the study of stellar populations of extra-galactic glob- ular clusters (GCs) by measuring spectral indices and comparing them to simple stellar population models. We present the study of GCs in the context of tracing elliptical galaxy star formation, chemical enrichment and mass assembly. In this thesis we set out to test how can be determined about a galaxy's formation history by studying the spectra of a small sample of GCs. Are the stellar population parameters of the GCs strongly linked with the formation history of the host galaxy? We present spectra and Lick index measurements for GCs associated with 3 el- liptical galaxies, NGC 1052, NGC 3379 and NGC 4649. We derive ages, metallicities and a-element abundance ratios for these GCs using the x2 minimisation approach of Proctor & Sansom (2002). The metallicities we derive are quite consistent, for old GCs, with those derived by empirical calibrations such as Brodie & Huchra (1990) and Strader & Brodie (2004). For each galaxy the GCs observed span a large range in metallicity from approximately [Z/H]=�2 to solar. We find that the majority of GCs are more than 10 Gyrs old and that we can- not distinguish any finer, age details amongst the old GC populations. However, amongst our three samples we find two age distributions contrary to our expecta- tions. From our sample of 16 GCs associated with the 1-2 Gyr old merger remnant NGC 1052, we find no young GCs. If a significant population of GCs formed during this merger we would expect those GCs to have low mass-to-light ratios and be included in our sample of bright GCs. We find 4 young GCs in our sample of 38 around NGC 4649, an old massive cluster elliptical. There are no signs of recent star formation and therefore we do not expect any GCs to have formed within the galaxy. These results seem to indicate that the GC systems of elliptical galaxies are not strongly associated with recent field star formation. We find a correlation between the α-element abundance ratio and the metallicity for all three samples. Using Thomas, Maraston & Korn (2004) models, we measure much higher α abundance ratios for low metallicity GCs than high metallicity GCs. With current data and models we are limited in both the accuracy and the detail with which we can probe this relationship. We suggest that there are some difficulties reconciling measured GC parameters with our expectations and propose some future work which could help to resolve these and other issues.

Observations of gravitationally microlensed quasars offer a unique opportunity to probe quasar structure on extremely small scales. In this thesis, we conduct extensive microlensing simulations and compare with observational data to constrain quasar accretion discs, and conduct preliminary probes of broad emission line region structure. This analysis is done using a new single-epoch imaging technique that requires very little telescope time, and yet produces results that are comparable to those obtained from long-term monitoring campaigns. / We begin by exploring the impact of variable smooth matter percentage and source size on microlensing simulations. Adding a smooth matter component affects minimum and saddle point images differently, broadening the magnification distribution for the saddle point image significantly. However, increasing the radius of the background source washes out this difference. The observation of suppressed saddle point images can therefore only be explained by microlensing with a smooth matter component if the background source is sufficiently small. We use these simulations, in combination with I-band imaging of the lensed quasar MG 0414+0534 to constrain the radius of the quasar source. This demonstrates the viability of a single-epoch imaging method for constraining quasar structure. / This technique is then expanded to single-epoch multi-band observations, in order to constrain the radial profile of quasar accretion discs as a function of observed wavelength. We present new Magellan observations of two gravitationally lensed quasars: MG 0414+0534 and SDSS J0924+0219. We also analyse two epochs of Q2237+0305 data obtained from the literature. Our results are compared with four fidicial accretion disc models. At the 95 per cent level, only SDSS J0924+0219 is inconsistent with any of the accretion disc models. When we combine the results from all three quasars -- a first step towards assembling a statistical sample -- we find that the two steepest accretion disc models are ruled out with 68 per cent confidence. / In addition, we are also able to use our microlensing simulations to constrain the smooth matter percentages in the lenses at the image positions. In both MG 0414+0534 and SDSS J0924+0219 we find smooth matter percentages that are inconsistent with zero. A smooth matter percentage of approximately 50 per cent is preferred in MG 0414+0534, and approximately 80 per cent in SDSS J0924+0219. Q2237+0305 is usually assumed to have a smooth matter percentage of zero at the image positions, as they lie in the bulge of the lensing galaxy. Though our measurement is consistent with a zero smooth matter percentage, there is a peak in the probability distribution at a value 20 per cent. This is perhaps a hint of additional intervening structures along the line of sight to the background quasar. / We test the sensitivity of our accretion disc constraints to a range of modelling parameters. These include errors in lens modelling, Bayesian prior probability selection, errors in observational data, and the microlens mass function. Constraints on the power-law index relating source radius to observed wavelength are found to be relatively unaffected by changes in the modelling parameters. Constraints on source radii are found to be more strongly affected. / Finally, the broad emission line region of Q2237+0305 is examined. Gemini IFU observations are presented clearly showing differential microlensing across the velocity profile of the CIII] emission line. To analyse this signature, we present three simple broad emission line region models: a biconical outflow, a Keplerian disc, and spherical infall. A method is developed to compare the shapes of simulated flux ratio spectra with the observed spectrum. We are unable to discriminate between the biconical outflow and Keplerian disc models when we average over all viewing angles and orientations. The spherical infall model, however, does not fit the observed data. We also find that for the non-spherically symmetric geometries, low inclination angles are essentially incompatible with the observations. This analysis offers hope that with sufficiently high signal-to-noise observations, differential microlensing signatures may allow us to constrain the geometry and kinematics of this poorly understood portion of quasar structure.

<p>It is an intriguing possibility that our world may consist of more than three spatial dimensions, compactified on such a small scale that they so far have escaped detection. In this thesis, a particular realization of this idea -- the scenario of so-called 'universal extra dimensions' (UED) -- is studied in some detail, with a focus on cosmological consequences and appplications.</p><p>The first part investigates whether the size of homogeneous extra dimensions can be stabilized on cosmological time scales. This is necessary in order not to violate the stringent observational bounds on a possible variation of the fundamental constants of nature.</p><p>An important aspect of the UED model is that it can provide a natural explanation for the mysterious dark matter, which contributes nearly thirty times as much as luminous matter like stars, galaxies etc. to the total energy content of the universe. In the second part of this thesis, the observational prospects for such a dark matter candidate are examined. In particular, it is shown how dark matter annihilations taking place in the Milky Way could give rise to exotic contributions to the cosmic ray spectrum in photons and antiprotons, leading to distinct experimental signatures to look for.</p><p>This includes a comparison with similar effects from other dark matter candidates, most notably the neutralino, which appears in supersymmetric extensions of the standard model of particle physics.</p>

The most popular way to achieve accelerated expansion of the universe is by introducing a scalar field in which motion of state varies with time. The accelerated expanded universe was first observed by Type Ia supernovae and future confirmed by the latest of CMB (Cosmic Microwave Background). The reason for the accelerated universe is the existence of dark energy. In this dissertation, we discuss the relationship between dark matter, dark energy, reheating and the standard model, and we find that it is possible for us to unify dark energy, dark matter and a reheating field into one scalar field. There is a very important stage called inflationary, and we find that the residue of the inflationary field, which is also described by a scalar field, can form bubbles in our universe due to the gravity force. We discuss that these bubbles are stable since they are trapped in their potential wells, and the bubbles can be a candidate for dark matter. We also discuss the scalar singlet filed, with the simplest interaction with the Higgs field, and we find that a static, classical droplet can be formed. The physics picture of the droplet is natural, and it is almost the same as the formation of an oil droplet in water. We show that the droplet is absolutely stable. Due to the very weak interaction with the Standard Model particles, the droplet becomes a very promising candidate for dark matter.

It is an intriguing possibility that our world may consist of more than three spatial dimensions, compactified on such a small scale that they so far have escaped detection. In this thesis, a particular realization of this idea -- the scenario of so-called 'universal extra dimensions' (UED) -- is studied in some detail, with a focus on cosmological consequences and appplications. The first part investigates whether the size of homogeneous extra dimensions can be stabilized on cosmological time scales. This is necessary in order not to violate the stringent observational bounds on a possible variation of the fundamental constants of nature. An important aspect of the UED model is that it can provide a natural explanation for the mysterious dark matter, which contributes nearly thirty times as much as luminous matter like stars, galaxies etc. to the total energy content of the universe. In the second part of this thesis, the observational prospects for such a dark matter candidate are examined. In particular, it is shown how dark matter annihilations taking place in the Milky Way could give rise to exotic contributions to the cosmic ray spectrum in photons and antiprotons, leading to distinct experimental signatures to look for. This includes a comparison with similar effects from other dark matter candidates, most notably the neutralino, which appears in supersymmetric extensions of the standard model of particle physics.

Though the arrival directions of ultra-high-energy cosmic rays (UHECRs) are distributed in a relatively isotropic manner, there is evidence of small-scale anisotropy. This, combined with the detection of cosmic rays with energies above the GZK cut-off, has motivated us to further investigate the idea that UHECRs are the result of a top-down mechanism involving the annihilation of superheavy dark matter particles in our galactic halo. To more precisely characterize the nature of dark matter, we have endeavoured to apply two different models to the leading UHECR spectra, namely those from the AGASA, High Resolution Flys Eye, and Pierre Auger Collaborations. First, we attempt a non-linear, least-squares fit of the particle physics fragmentation function to the spectra. Second, we propose that the observed cosmic ray spectrum above 3.5 × 10E+18 eV is the superposition of flux from two different sources: bottom-up acceleration via a simple power-law relation at lower energies and scattered particles from dark matter annihilation governed by fragmentation functions at higher energies. We find that while the former model does not provide a satisfactory fit to observatory data, the latter yields reduced χ2 values between 1.14 and 2.6. From the fragmentation function component of our second model, we are able to extract estimates of dark matter particle mass. We find values of (1.2 ± 0.6) 10E+21 eV, (5.0 ± 4.3) 10E+20 eV, and (2.6 ± 1.5) 10E+21 eV respectively for the AGASA, HiRes, and Pierre Auger data, which agree with earlier predictions based on a cosmological analysis of non-thermal particle production in an inflationary universe. Furthermore, we verify that the dark matter particle densities required by our two-source model are in line with current CDM theory.

The objective of this thesis is to derive a supersymmetric Lagrangian for fermionic fields with mass dimension one and to discuss their coupling to the O'Raifeartaigh model which is the simplest model permitting supersymmetry breaking. In addition it will be shown that eigenspinors of the charge conjugation operator (ELKO) exhibit a different transformation behaviour under discrete symmetries than previously assumed.<p> The calculations confirm that ELKO spinors are not eigenspinors of the parity operator and satisfy (<i>CPT</i>)² = - 1 which identifies them as representation of a nonstandard Wigner class. However, it is found that ELKO spinors transform symmetrically under parity instead of the previously assumed asymmetry. Furthermore, it is demonstrated that ELKO spinors transform asymmetrically under time reversal which is opposite to the previously reported symmetric behaviour. These changes affect the (anti)commutation relations that are satisfied by the operators acting on ELKO spinors. Therefore, ELKO spinors satisfy the same (anti)commutation relations as Dirac spinors, even though they belong to two different representations of the Lorentz group.<p> Afterwards, a supersymmetric model for fermionic fields with mass dimension one based on a general superfield with one spinor index is formulated. It includes the systematic derivation of all associated chiral and anti-chiral superfields up to third order in covariant derivatives. Starting from these fundamental superfields a supersymmetric on-shell Lagrangian that contains a kinetic term for the fermionic fields with mass dimension one is constructed. This on-shell Lagrangian is subsequently used to derive the on-shell supercurrent and to successfully formulate a consistent second quantisation for the component fields. In addition, the Hamiltonian in position space that corresponds to the supersymmetric Lagrangian is calculated. As the Lagrangian is by construction supersymmetric and the second quantisation of the component fields is consistent with their general supertranslations, the Hamiltonian is positive definite. This is confirmed by the results for the Hamiltonian in momentum space and the derivation of the creation and annihilation operators in momentum space. Based on these results, fermionic fields with mass dimension one represent an intriguing candidate for supersymmetric dark matter.<p> As an application the coupling of the fermionic fields with mass dimension one to the O'Raifeartaigh model is discussed. It turns out that the coupled model has two distinct solutions. The first solution representing a local minimum of the superpotential spontaneously breaks supersymmetry in perfect analogy to the O'Raifeartaigh model. The second solution is more intriguing as it corresponds to a global minimum of the superpotential. In this case the coupling to the fermionic sector restores supersymmetry. This is, however, achieved at the cost of breaking Lorentz invariance. Finally, the mass matrices for the multiplets of the coupled model are presented. It turns out that it contains two bosonic triplets and one fermionic doublet which are mass multiplets. In addition it contains a massless fermionic doublet as well as one fermionic triplet which is not a mass multiplet but rather an interaction multiplet that contains component fields of different mass dimension.<p> These results show that the presented model for fermionic fields with mass dimension one is a viable candidate for supersymmetric dark matter that could be accessible to experiments in the near future.

Different aspects of specific models in supersymmetry as well as constraints on decaying dark matter are analysed in this thesis. In chapter 1 we give a general introduction to supersymmetry, and briefly discuss some of the concepts that are used throughout the thesis. In chapter 2 we present a version of Gauge Mediated Supersymmetry Breaking which preserves an $R$-symmetry---the gauginos are Dirac particles, the $A$-terms are zero, and there are four Higgs doublets. This offers an alternative way for gauginos to acquire mass in the supersymmetry-breaking models of Intriligator, Seiberg, and Shih \cite{Intriligator:2006dd} . Additionally, we investigate the possibility of using $R$-symmetric gauge mediation to realise the spectrum and large sfermion mixing of the model of Kribs, Poppitz, and Weiner \cite{Kribs:2007ac}. In chapter 3 we investigate the Higgs sector of the $R$-symmetric model presented in chapter 2. Furthermore, a scan of the parameter space and sample spectra are provided. Other attributes like the tuning of the model are discussed. In chapter 4 we present a complete analysis of the cosmological constraints on decaying dark matter. In order to do this, we have updated and extended previous analyses to include Lyman-$\alpha$ forest, large scale structure, and weak lensing observations. Astrophysical constraints are not considered in this thesis. The bounds on the lifetime of decaying dark matter are dominated by either the late-time integrated Sachs-Wolfe effect for the scenario with weak reionization, or CMB polarisation observations when there is significant reionization. For the respective scenarios, the lifetimes for decaying dark matter are $\Gamma^{-1} \gtrsim 100$ Gyr and $ (f \Gamma) ^{-1} \gtrsim 5.3 \times 10^8$ Gyr (at 95.4\% confidence level), where the phenomenological parameter $f$ is the fraction of the decay energy deposited in baryonic gas. This allows us to constrain particle physics models with dark matter candidates through investigation of dark matter decays into Standard Model particles via effective operators. For decaying dark matter of $\sim 100$ GeV mass, we found that the size of the coupling constant in the effective dimension-4 operators responsible for dark matter decay has to generically be $ \lesssim 10^{-22}$.