Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 20 of 44 for “"Cosmological constant."”.
-
Theoretical and experimental approaches to the dark energy and the cosmological constant problem.
The cosmological constant problem is one of the most pressing problems of physics at this time. In this dissertation the problem and a set of widely-discussed theoretical solutions to this problem are reviewed. It is shown that a recently developed Lorentz gauge theory of gravity can provide a …
-
Measuring the Cosmological Constant Through the Lyman -Alpha Forest Using the Alcock -Paczynski Test
… O DM and OLambda. Among these, the cosmological constant OLambda, which associates with the vacuum energy of our universe, draws specific attentions for its importance in fundamental particle physics. The Lyalpha forest QSO spectra are observationally available from z ∼ 0 to z …
-
A study of chameleon-photon mixing from pulsars
… been proposed in literature, the simplest is the cosmological constant A. The cosmological constant lacks theoretical explanation for its extremely small value, thus dark energy is more generally modelled as a quintessence scalar field rolling down a flat potential.
-
Celestial Chiral Algebras and Self-Dual Gravity
… chapters, we discuss the presence of a non-zero cosmological constant, which has many subtleties. Twistor theory allows us to also include a cosmological constant in the self-dual Einstein equations, and after reviewing the relevant background material, we discuss how the cosmological constant …
-
Relevant Operators of Particle Physics and Cosmology
… which causes the "hierarchy problem", while the cosmological constant term of cosmology results in the "cosmological constant problem". In this thesis defense, I will discuss about how these issues can guide us in the pursuit of searching for new physics, both from a model building perspective …
-
Effective Field Theories in Cosmology
… the last 20 years, a large amount of detailed cosmological observations have promoted cosmology to the rank of high-precision science. Remarkably, all the observations currently available can be accounted for by assuming that (<em>i</em>) the universe is approximately homogeneous and isotropic …
-
Evolution of matter density perturbations in viable f (R) theories of gravity
… via a dark energy fluid in the form of a cosmological constant. Such a cosmological constant dominates the energy budget of the Universe today, and yet, it is still a poorly understood species because it is not observed yet. A competitive theoretical approach to understand this is via the …
-
Instabilities in asymptotically AdS spacetimes
… g \end{align*} with negative cosmological constant $\Lambda$. This has been motivated mainly by the conjectured instability of these solutions. The author of this thesis joins these efforts with two contributions, which are themselves independent of each other. In the first …
-
Rendering dark energy void
… and dark energy in the form of Einstein's cosmological constant A then implies that the latter contributes roughly 73% of the total energy of the universe, cold dark matter (CD'I) 23SiC, and baryons, the matter we are made, only 4%.
-
The measure problem in eternal inflation
… the probability distributions for the cosmological constant and for the curvature parameter. The former turns out to be such that the observed value of the cosmological constant is quite plausible. As for the curvature parameter, its distribution using the scale-factor measure predicts …
-
Kaluza-Klein Theories, Branes and Cosmology
… of the singularities. In order to approach the Cosmological Constant Problem and the related dark energy discussion in this context, we study the cosmology of a toy model, six-dimensional Einstein-Maxwell theory. The time independence of the deficit angle branes is proven. Some special cases are …
-
Effective loop quantization of black holes : a comparative analysis of quantization schemes.
… study all the solutions of LQBHs with constant polymerization parameters and find the classical singularity is always resolved. Additionally, assuming the black and white hole masses are equal, we identify a whole family of solutions that share all the desired properties of the …
-
A disformally coupled quintessence mimicking the ΛCDM background
… it cannot untangle the unknown nature of the cosmological constant in the Einstein Field Equations, which is responsible for the accelerated cosmological expansion. Secondly, it cannot explain the σ8 tension, which occurs because the constraints upon galactic clustering by the Cosmic Microwave …
-
Gauge theories of gravity
… group. Despite the introduction of Planck and cosmological constant scales through the torsion couplings, the linearised free theory is not only unitary but also power-counting renormalisable. A conformal symmetry in this regime is broken naturally in the nonlinear cosmology, for which constant …
-
Using gravitational lens geometry to measure cosmological parameters
We develop a technique for measuring cosmological parameters ([omega]M and w) using gravitational lens geometry, source and lens redshifts, and the velocity dispersion of the lensing galaxy. This technique makes use of the relation [theta][sub]E = 4[pi]... where the critical radius [theta][sub]E …
-
Beyond Standard Model Physics under the ground and in the sky
… models with light dilatons that ameliorate the cosmological constant problem by studying conformal phase transitions using holography. Finally, we have also checked the robustness of soft-wall geometry by including</p> <p>higher curvature terms in the five dimensional bulk action.</p>
-
Violating the Weak Cosmic Censorship Conjecture in Asymptotically Anti-de Sitter Space-Times
… dimensional General Relativity with negative cosmological constant, both with and without an electromagnetic field. Our results suggest that in both cases the space-time curvature can be made to grow without bound in a region visible to distant observers by imposing sufficiently violent …
-
BIANCHI-ICOSMOLOGICALMODEL IN f(R,T) GRAVITY
… associated with a cosmological constant, and the resulting standard cosmological model is called the ΛCDM model. This humongous episode confronted the fundamental theories of cosmology and astrophysics. Due to some shortcomings of the ΛCDM model, various alternatives …
-
Stationary Anti-de Sitter Black Hole Solutions in and out of Equilibrium
… the Einstein-Maxwell equations with a negative cosmological constant. The AdS/CFT correspondence has caused an upsurge in studying anti-de Sitter (AdS) space, and under this duality, the study of classical black holes corresponds to studying thermal states of very strongly coupled conformal …
-
Single-Fluid Approach to Modeling Dark Matter and Dark Energy
Cosmological observations over the past decades have provided overwhelming evidence for the ex istence of dark energy, a mysterious and dominant component responsible for the accelerated expan sion of the universe. The nature of dark energy remains one of the most intriguing puzzles in modern …
Page 1 of 3