In this thesis we investigate two approaches to quantum gravity. The first is the emergence of gravity from a discrete fundamental theory, and the second is the direct quantisation of gravity. For the first we develop tools to determine with relatively high accuracy the speed of propagation of information in collective modes which ultimately should give us some information about the emergent causal structure. We found a way of finding the dependence on the relative interaction strengths of the Hamiltonian and we also managed to calculate this speed in the case where the operators in the Hamitonian were not necessarily bounded. For the second approach, we investigated the phenomenology of Loop Quantum Gravity. We found that ultra light black holes (lighter than the Planck mass) have interesting new properties on top of being non-singular. First their horizon is hidden behind a Plancksized wormhole, second their specific heat capacity is positive and they are quasi-stable, they take an infinite amount of time evaporate. We investigated the dynamics of their collapse and evaporation explicitly seeing that not only was there no singularity, but there is also no information loss problem. Looking at how primordial black holes were in existence, we found that they might account for a significant portion of dark matter. And if they did, their radiation spectrum is such that the black holes in the dark matter halo of our galaxy could be the source for the ultra high energy cosmic rays we observe on earth.

The response of low energy nuclear recoil in NaI(Tl) is investigated in the following experiment. Such detectors have been used recently to search for evidence of dark matter in the form of weakly interacting massive particles (WIMPs). NaI(Tl) crystal response to nuclear recoil energy deposition is a key element in these searches. I discuss the cosmological and experimental motivations for these experiments, followed by an overview of the physics of direct detection and current relevant WIMP search experiments. With the experiment motivations covered, the details of NaI(Tl) detectors are reviewed. The specifics of our experiment are laid out including the neutron production, neutron beam calibration, shielding optimization, experimental design and setup. Then the crystal response calibration studies and Geant4 simulations are discussed followed by the final quenching factor values and uncertainties. This experiment measured quenching factors for sodium recoils in the energy range of (9 keV-40 keV) of 19%-27% QF. These results are similar to current published measurements. Interesting features of the QF measurements include an increase at low energies and a dip in the values at 30 keV, the iodine K-shell absorption edge. The goal of this experiment was to add valuable measurements of nuclear recoils at low energies that are relevant to low-mass WIMP experiments. Future plans will improve and expand on these measurements in order to better understand the response of NaI(Tl) at low energies.

As an alternative to dark matter, Modified Newtonian Dynamics (MOND) can explain dynamical measurements of galaxies on small scales. It is, however, unclear whether MOND still works for galaxies on the large scale. In this study, we use galaxy- galaxy (g-g) weak lensing measurements to examine MOND in the outer regions of galaxies. First, we study the amplitude of the weak gravitational lensing signal as a function of stellar mass around relatively isolated galaxies. We find that our measurements are inconsistent with the predictions from MOND. Second, we examine whether MOND can produce an anisotropic lensing signal as observed in the real data. Starting with a mass distribution of an extremely high ellipticity, we find it is very hard for MOND to reproduce the observed extensive anisotropic lensing signal from only the visible mass. Because the g-g lensing is measured at radii of up to hundreds of kiloparsecs, these two tests indicate that MOND does not work in outer regions of galaxies. Our study casts serious doubt on the notation that MOND can convincingly prove itself as a viable alternative to dark matter.

In this thesis jet production and cosmological constraints on decaying dark matter are studied. The powerful framework of effective field theory is applied in both cases to further our knowledge of particle physics. We first discuss how to apply the Soft Collinear Effective Theory (SCET) for calculating hadronic jet production rate. By applying SCET power counting, we develop a consistent approach to perform phase space integrations. This approach is then successfully applied to one-loop calculations with regard to a variety of jet algorithms. This allows us to study if the soft contribution can be factorized from the collinear ones. In particular we point out the connection between such factorization and the choice of ultraviolet regulator. We then further our study of the (exclusive) kt and C/A jet algorithms in SCET with the introduction of an additional regulator. Regularizing the virtualities and rapidities of graphs in SCET, we are able to write the next-to-leading-order dijet cross section as the product of separate hard, jet, and soft contributions. We show how to reproduce the Sudakov form factor to next-to-leading logarithmic accuracy previously calculated by the coherent branching formalism. Our resummed expression only depends on the renormalization group evolution of the hard function, rather than on that of the hard and jet functions as is usual in SCET. Finally we present a complete analysis of the cosmological constraints on decaying dark matter. For 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 constrained by Gamma^{-1} > 100 Gyr and (f*Gamma)^{-1} > 5.3 x 10^8 Gyr (at 95.4% confidence level), where the phenomenological parameter f is the fraction of decay energy deposited into the baryonic gas. This allows us to constrain particle physics models with dark matter candidates, by analyzing effective operators responsible for the dark matter decays into Standard Model particles.

The method of baryon acoustic oscillation (BAO) is among the best probes of the dark energy equation of state, and worldwide efforts are being invested in order to perform measurements that are accurate at the percent level. In current data analyses, however, estimates of the error about the BAO are based on the assumption that the density field can be treated as Gaussian, an assumption that becomes less accurate as smaller scales are included in the measurement. It was recently shown from large samples of N-body simulations that the error bars about the BAO obtained this way are in fact up to 15-20 per cent too small. This important bias has shaken the confidence in the way error bars are calculated, and is motivating developments of analyses pipelines that include non-Gaussian features in the matter density fields. In this thesis, we propose general strategies to incorporate non-Gaussian effects in the context of a survey. After describing the high performance N-body code that we used, we present novel properties of the non-Gaussian uncertainty about the matter power spectrum, and explain how these combine with a general survey selection function. Assuming that the non-Gaussian features that are observed in the simulations correspond to those of Nature, this approach is the first unbiased measurement of the error bar about the power spectrum, which simultaneously removes the undesired bias on the BAO error. We then relax this assumption about the similitude of the non-Gaussian natures in simulations and data, and develop tools that aim at measuring the non-Gaussian error bars exclusively from the data. It is possible to improve the constraining power of non-Gaussian analyses with `Gaussianizations' techniques, which map the observed fields into something more Gaussian. We show that two of such techniques maximally recover degrees of freedom that were lost in the gravitational collapse. Finally, from a large sample of high resolution N-body realizations, we construct a series of weak gravitational lensing distortion maps and provide high resolution halo catalogues that are used by the CFTHLenS community to calibrate their estimators and study many secondary effects with unprecedented accuracy.

In this thesis jet production and cosmological constraints on decaying dark matter are studied. The powerful framework of effective field theory is applied in both cases to further our knowledge of particle physics. We first discuss how to apply the Soft Collinear Effective Theory (SCET) for calculating hadronic jet production rate. By applying SCET power counting, we develop a consistent approach to perform phase space integrations. This approach is then successfully applied to one-loop calculations with regard to a variety of jet algorithms. This allows us to study if the soft contribution can be factorized from the collinear ones. In particular we point out the connection between such factorization and the choice of ultraviolet regulator. We then further our study of the (exclusive) kt and C/A jet algorithms in SCET with the introduction of an additional regulator. Regularizing the virtualities and rapidities of graphs in SCET, we are able to write the next-to-leading-order dijet cross section as the product of separate hard, jet, and soft contributions. We show how to reproduce the Sudakov form factor to next-to-leading logarithmic accuracy previously calculated by the coherent branching formalism. Our resummed expression only depends on the renormalization group evolution of the hard function, rather than on that of the hard and jet functions as is usual in SCET. Finally we present a complete analysis of the cosmological constraints on decaying dark matter. For 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 constrained by Gamma^{-1} > 100 Gyr and (f*Gamma)^{-1} > 5.3 x 10^8 Gyr (at 95.4% confidence level), where the phenomenological parameter f is the fraction of decay energy deposited into the baryonic gas. This allows us to constrain particle physics models with dark matter candidates, by analyzing effective operators responsible for the dark matter decays into Standard Model particles.

The method of baryon acoustic oscillation (BAO) is among the best probes of the dark energy equation of state, and worldwide efforts are being invested in order to perform measurements that are accurate at the percent level. In current data analyses, however, estimates of the error about the BAO are based on the assumption that the density field can be treated as Gaussian, an assumption that becomes less accurate as smaller scales are included in the measurement. It was recently shown from large samples of N-body simulations that the error bars about the BAO obtained this way are in fact up to 15-20 per cent too small. This important bias has shaken the confidence in the way error bars are calculated, and is motivating developments of analyses pipelines that include non-Gaussian features in the matter density fields. In this thesis, we propose general strategies to incorporate non-Gaussian effects in the context of a survey. After describing the high performance N-body code that we used, we present novel properties of the non-Gaussian uncertainty about the matter power spectrum, and explain how these combine with a general survey selection function. Assuming that the non-Gaussian features that are observed in the simulations correspond to those of Nature, this approach is the first unbiased measurement of the error bar about the power spectrum, which simultaneously removes the undesired bias on the BAO error. We then relax this assumption about the similitude of the non-Gaussian natures in simulations and data, and develop tools that aim at measuring the non-Gaussian error bars exclusively from the data. It is possible to improve the constraining power of non-Gaussian analyses with `Gaussianizations' techniques, which map the observed fields into something more Gaussian. We show that two of such techniques maximally recover degrees of freedom that were lost in the gravitational collapse. Finally, from a large sample of high resolution N-body realizations, we construct a series of weak gravitational lensing distortion maps and provide high resolution halo catalogues that are used by the CFTHLenS community to calibrate their estimators and study many secondary effects with unprecedented accuracy.

Thesis (M.Sc.) - Carleton University, 2008. / Includes bibliographical references (p. 75-79). Also available in electronic format on the Internet.

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Physics and Astronomy." Includes bibliographical references.

Thesis (doctoral)--Rijksuniversiteit Groningen, 1992. / Summary in Dutch. Includes bibliographical references.