1,720,966 research outputs found
THE WARPING OF EXTRA SPACES ACCELERATES THE EXPANSION OF THE UNIVERSE
No full text Generic cosmological models derived from higher-dimensional theories with warped extra-dimensions have a nonzero cosmological constant-like term induced on the 3 + 1 space–time, or a physical three-brane. In the scenario where this 3 + 1 space–time is an inflating de Sitter "bran" embedded in a higher-dimensional space–time, described by warped geometry, the four-dimensional cosmological term is determined in terms of two length scales: one is a scale associated with the size of extra-dimension(s) and the other is a scale associated with the warping of extra-space(s). The existence of this term in four dimensions provides a tantalizing possibility of explaining the observed accelerating expansion of the universe from fundamental theories of gravity, e.g. string theory. </jats:p
The Dark Energy Problem: An Inspiration for New Physics
No full textAs much as physics has advanced in the 20th century and the beginning of the current one, reaching astounding accuracy when comparing modern theories of particle physics and general relativity to experimental results, there has been a signi cant progress in observational and theoretical cosmology. Despite these progresses, we have not been able to account for what seems to be nearly 73% of the energy budget of the universe and hence its mystic name 'dark energy'. The dark energy problem provides an inspiration for seeking new laws or symmetries in nature: more precisely, a search for concise and fundamentally simple relationship between the 4D Planck mass and the present size of the universe (or the present value of the Hubble expansion parameter).Keywords: Observational and theoretical cosmology; Dark energy; 4D Planck massThe Himalayan Physics Vol.2, No.2, May, 2011Page: 57-60Uploaded Date: 1 August, 2011</jats:p
The Quest for a Realistic Four-dimensional Cosmology
No full textThe existence of a small and positive cosmological constant attributed to gravitational vacuum energy (or dark energy) in the present-day universe appears to be the most pressing obstacle as well as opportunity to significantly improving the models of four-dimensional cosmology from fundamental theories of gravity, including string theory and modern Kaluza-Klein theories. In seeking to resolve this problem, one naturally wonders if the real world can somehow be interpreted as an inflating de Sitter "brane" embedded in a five or even higher-dimensional space-time described by warped or non-factorizable geometry. In this scenario, the four-dimensional cosmological constant may well be determined in terms of two length scales: one is a scale associated with the size of extra dimensions and the other is a scale associated with the expansion rate of the universe, which is also related to the warping of extra spaces.Key words: CosmologyThe Himalayan Physics Vol.1, No.1, May, 2010Page: 18-24Uploaded Date: 28 July, 2011</jats:p
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