Acceleration from M theory and Fine-tuning

Abstract

The compactification of M theory with time dependent hyperbolic internal space gives an effective scalar field with exponential potential which provides a transient acceleration in Einstein frame in four dimensions. Ordinary matter and radiation are present in addition to the scalar field coming from compactification. We find that we have to fine-tune the initial conditions of the scalar field so that our Universe experiences acceleration now. During the evolution of our Universe, the volume of the internal space increases about 12 times. The time variation of the internal space results in a large time variation of the fine structure constant which violates the observational constraint on the variation of the fine structure constant. The large variation of the fine structure constant is a generic feature of transient acceleration models.

9 pages, 3 figures, use iopart, v2; references updated, accepted for publication in Class. Quantum Grav

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• Star Models with Dark Energy
• Noether Symmetry Approach in multiple scalar fields Scenario
• On Anisotropic Dark Energy
• Fixed points in interacting dark energy models
• Cosmological constant and late transient acceleration of the universe in the Horava-Witten Heterotic M-Theory on S^{1}/Z_{2}
• The dynamical behavior of the Extended Holographic Dark Energy with Hubble Horizon
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• Orbifold Branes in the $M_D\times M_{d^{+}}\times M_{d^{-}}$ Compactification of type II string on $S^1/Z_2$ and their cosmological applications