Related papers: Constraints on a quintessence model from gravitati…
The recent GW170817 measurement favors the simplest dark energy models, such as a single scalar field. Quintessence models can be classified in two classes, freezing and thawing, depending on whether the equation of state decreases towards…
Here we present a pilot study into whether elliptical galaxy counts alone, can place a useful constraint on the Omega_M - Omega_Lambda-plane. The elliptical galaxy counts are drawn from three surveys: The Millennium Galaxy Catalogue (16 >…
Thawing quintessence scalar field models with the various potential forms to explain the late-time cosmic acceleration are compared to the {\Lambda}CDM model in detail by analyzing cosmological parameters with a set of observational data…
We propose a possible measurement of the time variability of the vacuum energy using strong gravitational lensing events. As an example we take an Einstein cross lens HST 14176+5226 and demonstrate that the measurement of the velocity…
Weak gravitational lensing observations probe the spectrum and evolution of density fluctuations and the cosmological parameters which govern them but are currently limited to small fields and subject to selection biases. We show how the…
Density fluctuations in the matter distribution lead to distortions of the images of distant galaxies through weak gravitational lensing effects. This provides an efficient probe of the cosmological parameters and of the density field. In…
We investigate a quintessence model involving two scalar fields with double-exponential potentials. This configuration allows the system as a whole to emulate the dynamics of a single field with a shallower potential, enabling scalar fields…
We use recent results from the Wilkinson Microwave Anisotropy Probe (WMAP) for the locations of peaks and troughs of the Cosmic Microwave Background (CMB) power spectrum, together with constraints from large-scale structure, to study a…
We study the cosmological evolution of scalar fields that arise from a phase transition at some energy scale $\Lm_c$. We focus on negative power potentials given by $V=c\Lm_c^{4+n}\phi^{-n}$ and restrict the cosmological viable values of…
Applying the distance sum rule in strong gravitational lensing (SGL) and type Ia supernova (SN Ia) observations, one can provide an interesting cosmological model-independent method to determine the cosmic curvature parameter $\Omega_k$. In…
We present a new geometrical method which uses weak gravitational lensing effects in clusters to constrain the cosmological parameters Omega and Lambda. On each background galaxy, a cluster induces a convergence and a shear terms, which…
We derive new approximations for quintessence solutions that are simpler and an order of magnitude more accurate than anything available in the literature, which from an observational perspective \emph{makes numerical calculations…
We study with semi-analytical methods the statistics of pronounced arcs caused by lensing of galaxies by foreground galaxy clusters. For the number density and redshift distribution of rich clusters we use Press-Schechter theory, normalized…
The present day observations favour a universe which is flat, accelerated and composed of $\sim 1/3$ matter (baryonic + dark) and $\sim 2/3$ of a negative pressure component, usually referred to as dark energy or quintessence. The Cosmic…
We explore the dependence of weak lensing phenomena on the background cosmology. We first generalise the relation between $P_\psi(\omega)$, the angular power spectrum of the distortion, and the power spectrum of density fluctuations to…
We examine the prospect of using the observed abundance of weak gravitational lenses to constrain the equation-of-state parameter w of the dark energy. Here we solve the spherical-collapse model with dark energy, clarifying some ambiguities…
We present constraints on extensions to the flat $\Lambda$CDM cosmological model by varying the spatial curvature $\Omega_K$, the sum of the neutrino masses $\sum m_\nu$, the dark energy equation of state parameter $w$, and the Hu-Sawicki…
We have measured a velocity dispersion for the foreground galaxy in this gravitationally lensed system. Our dispersion confirms the prediction from lens models, provided that the source is distant enough ($z_{_S}>0.2$). Current…
The self-accelerating braneworld model (DGP) seems to provide a simple alternative to the the standard $\Lambda$CDM cosmology to explain the current cosmic acceleration, which is strongly indicated by measurements of Type Ia supernovae, as…
Inspired by the string axiverse idea, it has been suggested that the recent transition from decelerated to accelerated cosmic expansion is driven by an axion-like quintessence field with a sub-Planckian decay constant. The scenario requires…