Related papers: Accelerated Universes from type IIA Compactificati…
The unexpected faintness of high-redshift Type Ia supernovae (SNe Ia), as measured by two teams, has been interpreted as evidence that the expansion of the Universe is accelerating. We review the current challenges to this interpretation…
In the context of Horndeski cosmologies, we consider a dynamical adjustment mechanism able to screen any value of the vacuum energy of the matter fields leading to a fixed de Sitter geometry. Thus, we present the most general scalar-tensor…
We explore the cosmological content of Salam-Sezgin six dimensional supergravity, and find a solution to the field equations in qualitative agreement with observation of distant supernovae, primordial nucleosynthesis abundances, and recent…
We study supersymmetric compactifications of type II strings on eightfolds to two dimensions. It is demonstrated that the type IIB string on an eightfold is free of gravitational anomalies. T-duality requires that this theory when further…
We analyse various two dimensional theories arising from compactification of type II and heterotic string theory on asymmetric orbifolds. We find extra supersymmetry generators arising from twisted sectors, giving rise to exotic…
In the context of realizing de-Sitter vacua and the slow-roll inflation, several no-go conditions have been found in the framework of type IIA (generalized) flux compactifications. In this article, using our recently proposed $T$-dual…
We discuss non-supersymmetric attractors with an instanton correction in Type IIA string theory compactified on a Calabi-Yau three-fold at large volume. For a stable non-supersymmetric black hole, the attractor point must minimize the…
The current observations are usually explained by an accelerating expansion of the present universe. However, with the present quality of the supernovae Ia data, the allowed parameter space is wide enough to accommodate the decelerating…
We study Kaluza-Klein cosmology in cuscuton gravity and find an exact solution describing an accelerating 4-dimensional universe with a stable extra dimension. A cuscuton which is a non-dynamical scalar field is responsible for the…
We point out that the recently proposed model of a flat 4-dimensional universe with accelerated expansion in string/M-theory is a special case of time-dependent solutions that the author found under the name of ``S-branes.'' We also show…
The problem of solving perturbatively the equations describing the evolution of self-gravitating collisionless matter in an expanding universe considerably simplifies when directly formulated in terms of the gravitational and velocity…
We present a local-to-global cosmological framework in which cosmic acceleration emerges from structure formation in an inhomogeneous Einstein-de Sitter (iEdS) universe, without dark energy. The model exhibits a quasilinear coasting…
We propose a candidate for the dual (in the weak/strong coupling sense) of the six-dimensional heterotic string compactification constructed recently by Chaudhuri, Hockney and Lykken. It is a type IIA string theory compactified on an…
We find de Sitter and flat space solutions with all moduli stabilized in four dimensional supergravity theories derived from the heterotic and type II string theories, and explain how all the previously known obstacles to finding such…
Gravitational theories differing from General Relativity may explain the accelerated expansion of the Universe without a cosmological constant. However, to pass local gravitational tests, a "screening mechanism" is needed to suppress, on…
In the contemporary Universe, most galaxies are supported by ordered rotation, yet a significant subset of the most massive and quiescent systems are dominated by random stellar motions and classified as slow rotators. These galaxies are…
We consider multidimensional gravity with a Lagrangian containing the Ricci tensor squared and the Kretschmann invariant. In a Kaluza-Klein approach with a single compact extra space of arbitrary dimension, with the aid of a slow-change…
The possibility of an expanding decelerating Universe in the distant future is investigated in the context of a quintessence scalar field cosmology. Such a conceivable evolution is tested against SNe Ia and $H(z)$ cosmic chronometers data,…
As shown by Parker and Raval, quantum field theory in curved spacetime gives a possible mechanism for explaining the observed recent acceleration of the universe. This mechanism, which differs in its dynamics from quintessence models,…
This is a pedagogical review of the recent observational data obtained from type Ia supernova surveys that support the accelerating expansion of the universe. The methods for the analysis of the data are reviewed and some of the theoretical…