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The distribution of galaxies in the Universe is not random: rather, galaxies cluster in a structured way. The formation and growth of these large-scale structures (LSS) provides powerful dynamical probes for cosmology. This thesis explores two of these probes, namely redshift-space distortion (RSD) and the imprints of LSS on the Cosmic Microwave Background (CMB). Using galaxy surveys, I test the theory of structure growth in the context of the ΛCDM cosmological model. RSD probes the velocity field of LSS, which is influenced by the growth of matter fluctuations. I use the galaxy and group catalogues in GAMA survey to test the robustness of RSD in recovering unbiased growth rate fσ8 with different tracers. Specifically, galaxies are split into red and blue subsamples, and groups are divided into three stellar mass bins. The 2D group-galaxy cross-correlation function between these subsamples are interpreted by a linear model and a small-scale Finger of God convolution. Given an appropriate minimum fitting scale, I show that the subsamples give consistent growth rate, fσ8 = 0.25 ± 0.15, also in agreement with the Planck 2018 results. The imprints of LSS on the CMB correspond to the effects of weak gravitational lensing and the Integrated Sachs-Wolfe (ISW) effect. I measure these effects using the public DESI Legacy Survey, exploiting its large sky coverage and substantial depth for tomographic studies. After careful selection of galaxies and correction for various systematic effects, I assign photometric redshifts to galaxies based on g − r, r − z, and z − W1 colours, and construct four tomographic redshift bins in 0 < z < 0.8. The photo-z errors are accounted for using the galaxy auto- and cross-correlations between these redshift bins. Having a clean galaxy sample, I measure the cross-correlation C` between the galaxy density fields and the Planck CMB temperature and lensing convergence maps. The amplitudes of these measurements relative to the ΛCDM prediction using the fiducial Planck 2018 best-fit cosmology are Aκ = 0.901 ± 0.026 and AISW = 0.98 ± 0.35. While the ISW result is consistent with the fiducial cosmology, the CMB lensing result is noticeably lower. This low amplitude is interpreted in terms of a lower Ωm in combination with the total CMB lensing constraints. Finally, to address the excess stacked ISW signal from supervoids claimed in literature, I construct a superstructure catalogue using the four tomographic bins in the DESI Legacy Survey, and measure their stacked CMB lensing and ISW signals. The results are compared to the ΛCDM prediction from a mock catalogue that is based on N-body simulations and carefully matched to the data. I find a similar discrepancy in the lensing amplitude as in the cross-correlation scenario. Here, it is mainly contributed by density peaks at the higher redshift end. I also show that the detection of ISW signal from superstructure stacking is only mild, but is consistent with the ΛCDM prediction with a 95% upper limit of AISW = 1.51 using the full sample. Testing a range of superstructure subsamples, I demonstrate that the claimed excess signal may be due to look-elsewhere effect.

Despite the many successes of the current standard model of cosmology on the largest physical scales, it relies on two phenomenologically motivated constituents, cold dark matter and dark energy, which account for approximately 95% of the energy-matter content of the universe. From a more fundamental point of view, however, the introduction of a dark energy (DE) component is theoretically challenging and extremely fine-tuned, despite the many proposals for its dynamics. On the other hand, the concept of cold dark matter (CDM) also suffers from several issues such as the lack of direct experimental detection, the question of its cosmological abundance and problems related to the formation of structure on small scales. A perhaps more natural solution might be that the gravitational interaction genuinely differs from that of general relativity, which expresses itself as either one or even both of the above dark components. Here we consider different possibilities on how to constrain hypothetical modifications to the gravitational sector, focusing on the subset of tensor-vector-scalar (TeVeS) theory as an alternative to CDM on galactic scales and a particular class of chameleon models which aim at explaining the coincidences of DE. Developing an analytic model for nonspherical lenses, we begin our analysis with testing TeVeS against observations of multiple-image systems. We then approach the role of low-density objects such as cosmic filaments in this framework and discuss potentially observable signatures. Along these lines, we also consider the possibility of massive neutrinos in TeVeS theory and outline a general approach for constraining this hypothesis with the help of cluster lenses. This approach is then demonstrated using the cluster lens A2390 with its remarkable straight arc. Presenting a general framework to explore the nonlinear clustering of density perturbations in coupled scalar field models, we then consider a particular chameleon model and highlight the possibility of measurable effects on intermediate scales, i.e. those relevant for galaxy clusters. Finally, we discuss the prospects of applying similar methods in the context of TeVeS and present an ansatz which allows to cast the linear perturbation equations into a more convenient form.

This dissertation addresses two aspects of the theory and simulation of stress-diffusion coupling in semiconductors. The first part is a study of the role of kinetics in the formation of pits in stressed thin films. The second part describes how atomic-scale calculations can be used to extract the thermodynamic and elastic properties of point-defects. For both aspects, there exists an interaction between phenomena at the atomic and macroscopic scales and the formation of both point-defects and surface features depends on the stress state of the system. Recently, pit nucleation has been observed in a variety of semiconductor thin films. We present a model for pit nucleation in which the adatom concentration plays a central role in controlling the morphological development of the surface. Although pits relieve elastic energy more efficiently than islands, pit nucleation can be prevented by a high adatom concentration. Three-dimensional islands act as adatom sinks and the lower adatom density in their vicinity promotes pit nucleation. Thermodynamic considerations predict several different growth regimes in which pits may nucleate at different stages of growth depending on the growth conditions and materials system. When kinetics are taken into account, the model predicts a wide range of possible morphologies: planar films, islands alone, island nucleation followed by pit nucleation, and pits alone. The model shows good agreement with experimental observations in III-V systems given the uncertainties in quantifying experimental parameters such as the surface energy. The same stresses which lead to the nucleation of surface features can have a significant effect on the stability of dopant profiles by altering diffusivities and by inducing chemical potential gradients. We perform empirical calculations regarding a simple model point-defect, a vacancy in the Stillinger Weber model of silicon. In the context of these calculations we devise a method to extract the strength of the elastic relaxation in the vicinity of the defect. This quantity is extracted from the leading order term which must be evaluated sufficiently far from the defect and the boundaries. It is also directly related to the formation volume, the thermodynamic quantity that couples the defect free energy to the externally applied stress.