Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Conference Object Stress-Energy Connection: Degravitating the Vacuum Energy(World Scientific Publishing Co. Pte Ltd, 2013) Demir, Durmuş AliThis talk summarizes recent studies on the gravitational properties of vacuum energy in a non-Riemannian geometry formed by the stress-energy tensor of vacuum, matter and radiation. Postulating that the gravitational effects of matter and radiation can be formulated by an appropriate modification of the spacetime connection, we obtain varied geometro-dynamical equations which properly comprise the usual gravitational field equations with, however, Planck-suppressed, non-local, higher-dimensional additional terms. The prime novelty brought about by the formalism is that, the vacuum energy does act not as the cosmological constant but as the source of the gravitational constant. The formalism thus deafens the cosmological constant problem by channeling vacuum energy to gravitational constant. Nevertheless, quantum gravitational effects, if any, restore the problem via the graviton and graviton-matter loops, and the mechanism proposed here falls short of taming such contributions to cosmological constant.Article Citation - WoS: 17Citation - Scopus: 19Cosmological Consequences of a Variable Cosmological Constant Model(World Scientific Publishing Co. Pte Ltd, 2017) Azri, Hemza; Bounames, A.We derive a model of dark energy which evolves with time via the scale factor. The equation-of-state is studied as a function of a parameter α introduced in this model as = (1 - 2α)/(1 + 2α). In addition to the recent accelerated expansion, the model predicts another decelerated phase. These two phases are studied via the parameter α. The age of the universe is found to be almost consistent with the observation. In the limiting case, the cosmological constant model, we find that vacuum energy gravitates with a tiny gravitational constant which evolves with the scale factor, rather than with Newton's constant. This enables degravitation of the vacuum energy which in turn produces the tiny observed curvature, rather than a 120 orders of magnitude larger value.