Archivi tag: theories of gravity

AdS/CFT, self-adjoint extension and the resolution of cosmological singularities

In the context of Einstein gravity coupled to matter satisfying fairly general energy conditions, cosmological singularities are unavoidable, as was proven by Hawking and Penrose many year ago. One of the hopes for superstring theory is that a solution to this problem may be found. Clearly, however, a non-perturbative formulation of string theory must be used. The AdS/CFT correspondence is a proposed definition of non-perturbative string theory (including gravity) in terms of a conformal field theory which does not involve gravity. It has been conjectured that the AdS/CFT correspondence can be used to resolve cosmological singularities. Initial work in this direction was done by different groups, including Craps-Hertog-Turok, Khoury-Ovrut-Steinhardt-Turok, Skenderis-McFadden, Silverstein-Horowitz and Das-Tridevi. Continua a leggere AdS/CFT, self-adjoint extension and the resolution of cosmological singularities


Drifting through the Cosmic Web

The Large Scale Structure of the Universe (LSS) was first discussed at the IAU Symposium No. 79 in 1977 in Tallinn. The title of the Symposium : “The Large Scale Structure of the Universe” , was the first official use of this term (J. Einasto). Since then, it has been of major interest in cosmology. This large scale pattern, emerged from the primordial density fluctuations of dark matter under the effect of gravity, is composed of nodes, filaments and walls surrounding large voids: it is a vast foam-like structure, aka the “cosmic web”, which provides constraints on the content of the universe and the nature of its components. Continua a leggere Drifting through the Cosmic Web

Cosmology on Safari

The past decade has seen a significant growth in cosmological observations that have placed increasingly tighter constraints on the cosmological model and the basic parameters that describe it. While we have an excellent phenomenological model a more fundamental picture is largely missing, considering both the very earliest times where high-energy processes are relevant and in the late-time universe, where we are in the curious position of living in a universe that is 95% dark. Continua a leggere Cosmology on Safari

Fundamental Issues of the Standard Cosmological Model

The Planck Satellite measurement have increased the accuracy of cosmological observations to a level which allows to constrain cosmological models with unprecedented precision. The aim of this workshop is to discuss the implications of these recent results combined with other (i.e. Planck, but also WMAP, galaxy surveys, SNIa data…) on models that aim at describing the primordial epochs and the origin and formation of large scale structures of the Universe. Continua a leggere Fundamental Issues of the Standard Cosmological Model