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The introduction of electroweak multiplets that transform under any representation of the standard $SU(2)_L$ gauge group suggests the existence of electrically neutral stable particles capable of serving as cold dark matter in the…

We explore the possibility that (Bose-Einstein) condensation of scalar fields from string compactifications can lead to long-lived compact objects. Depending on the type of scalar fields we find different realisations of star-like and…

We study a phenomenological class of models where dark matter converts to dark radiation in the low redshift epoch. This class of models, dubbed DMDR, characterizes the evolution of comoving dark matter density with two extra parameters,…

Exotic dark matter together with the vacuum energy or cosmological constant seem to dominate in the Universe. An even higher density of such matter seems to be gravitationally trapped in the Galaxy. Thus its direct detection is central to…

The subject of this thesis is cosmological implications of string compactifications understood in a broad sense. In the first half of the thesis, we will begin by reviewing the four-dimensional description of the tree-level perturbative…

The current paradigm for dark matter direct detection is to assume that the dark sector is solely composed of a single particle species. In this short paper, we make the observation that dark matter comprising both a light and a heavy…

Recent developments in string theory have led to "realistic" string compactifications which lead to moduli stabilization while generating a hierarchy between the Electroweak and Planck scales at the same time. However, this seems to suggest…

The effects of particle discreteness in N-body simulations of Lambda Cold Dark Matter (LambdaCDM) are still an intensively debated issue. In this paper we explore such effects, taking into account the scatter caused by the randomness of the…

Dark radiation, parameterized in terms of $N_{\rm eff}$, has been considered many times in the literature as a possible remedy in alleviating the Hubble constant ($H_0$) tension. We review here the effect of such an extra dark radiation…

We introduce a natural model of quintessence in string theory where the light rolling scalar is radiatively stable and couples to Standard Model matter with weaker-than- Planckian strength. The model is embedded in an anisotropic type IIB…

We present new constraints on the relativistic neutrino effective number N_eff and on the Cosmic Microwave Background power spectrum lensing amplitude A_L from the recent Planck 2013 data release. Including observations of the CMB large…

We present here bounds on neutrino masses from the combination of recent Planck Cosmic Microwave Background measurements and galaxy clustering information from the Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital…

We discuss variants of Cold Dark Matter (CDM) dominated cosmological models that give good agreement with a range of observations. We consider models with hot dark matter, tilt, $\Omega < 1$, or a cosmological constant. We also discuss the…

In the D = (n + m + 1) dimensional brane world scenario with m compact dimensions, the radion modulus can be stabilised by a massive bulk m-form antisymmetric field. We analyse some of the phenomenological aspects of this scenario. We find…

The cold dark matter (CDM) scenario has proved successful in cosmology. However, we lack a fundamental understanding of its microscopic nature. Moreover, the apparent disagreement between CDM predictions and subgalactic-structure…

We propose a minimal gauged $U(1)_{B-L}$ extension of the minimal supersymmetric Standard Model (MSSM) which resolves the cosmological moduli problem via thermal inflation, and realizes late-time Affleck-Dine leptogensis so as to generate…

A dark radiation term arises as a correction to the energy momentum tensor in the simplest five-dimensional RS-II brane-world cosmology. In this paper we revisit the constraints on dark radiation based upon the newest results for…

This is a review of the Cold Dark Matter model of structure formation, and its variants. The approach is largely from first principles, the main aim being to impart a basic understanding of the relevant theory with an eye to the likely…

We address the cosmological moduli/gravitino problems and the issue of too little thermal but excessive non-thermal dark matter from the decays of moduli. The main examples we study are the G2-MSSM models arising from M theory…

We determine constraints on spatially-flat tilted dynamical dark energy XCDM and $\phi$CDM inflation models by analyzing Planck 2015 cosmic microwave background (CMB) anisotropy data and baryon acoustic oscillation (BAO) distance…