Emergent Gravity: String Theory Without String Theory

Classical and Quantum Gravity, 2005

We study the cosmological evolution based upon a $D$-dimensional action in low-energy effective string theory in the presence of second-order curvature corrections and a modulus scalar field (dilaton or compactification modulus). A barotropic perfect fluid coupled to the scalar field is also allowed. Phase space analysis and the stability of asymptotic solutions are performed for a number of models which include ($i$) fixed scalar field, ($ii$) linear dilaton in string frame, and ($iii$) logarithmic modulus in Einstein frame. We confront analytical solutions with observational constraints for deceleration parameter and show that Gauss-Bonnet gravity (with no matter fields) may not explain the current acceleration of the universe. We also study the future evolution of the universe using the GB parametrization and find that big rip singularities can be avoided even in the presence of a phantom fluid because of the balance between the fluid and curvature corrections. A non-minimal coupling between the fluid and the modulus field also opens up the interesting possibility to avoid big rip regardless of the details of the fluid equation of state.

2007

We address issues on the origin of gravity and the cosmological constant problem based on a recent understanding about the correspondence between noncommutative field theory and gravity. We suggest that the cosmological constant problem can be resolved in a natural way if gravity emerges from a gauge theory in noncommutative spacetime. Especially, we elucidate why the emergent gravity implies that vacuum energy does not gravitate but only fluctuations around the vacuum generate gravity. That is, a flat spacetime emerges from uniform condensation of energy, previously identified with the cosmological constant.

2009

We discuss the main cosmological implications of considering string-loop effects and a potential for the dilaton in the lowest order string effective action. Our framework is based on the effective model arising from regarding homogeneous and isotropic dilaton, metric and Yang-Mills field configurations. The issues of inflation, entropy crisis and the Polonyi problem as well as the problem of the cosmological constant are discussed.

arXiv (Cornell University), 2006

The inflation field is generalized as a local field with eight Goldstone phases if the Lorentz group is spontaneously broken in the vacuum in addition to an internal symmetry group in the Planck era inflation quantum vacuum phase transition. This permits the emergence of the Einstein Cartan tetrad field with the six extra dimensions of the Calabi Yau space associated with a massive torsion field when the full Poincare group is locally gauged. These conjectures also lead naturally to the quantization of area, the world hologram and the prediction that both the LHC and any other DM detectors will not find any legitimate dark matter particles as a matter of fundamental principle.

Arxiv preprint hep-th/0002094

3.1 Generic asymptotically trivial past . . . . . . . . . . . . . . . . . . 596 3.2 The asymptotic past's effective action and different (conformal) frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 3.3 Classical asymptotic symmetries: The importance of SUSY . . . . 598 3.4 Dilaton-driven inflation as ...

String Gravity and Physics at the Planck Energy Scale, 1996

After recalling a few basic concepts from cosmology and string theory, I will discuss the main ideas/assumptions underlying string cosmology and show how these lead to a two-parameter family of "minimal" models. I will then explain how to compute, in terms of those parameters, the spectrum of scalar, tensor and electromagnetic perturbations, point at their (T and S-type) duality symmetries, and mention their most relevant physical consequences.

2011

General relativity and various possibilities about its proper combination with Quantum mechanics is a central topic in theoretical physics. In this article we explain various links which bridge between different views about Quantum Gravity theories. It turns out that these have very close relation with different interpretations about what quantization mean.We try to justify basic questions like what a string tension mean. First, we start with qualitative analysis and then we confirm these with quantitative results. These are shown to have relation with Quantum Gravity noise, Dark Energy, Hogan’s noise and the Holographic principle. We clarify a long standing confusion in entropic Gravity, whether increase in entropy (4s) makes the particle to move (4x) or vice-versa. We indicate the possibility about non-local entanglement operation carried out by space-time which will increase entropy and a particle in space will move causing 4x. We relate noise with dissipation, much like a statis...

Physical Review D, 2007

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 measurements of the cosmic microwave background. The carrier of the acceleration in the present de Sitter epoch is a quintessence field slowly rolling down its exponential potential. Intrinsic to this model is a second modulus which is automatically stabilized and acts as a source of cold dark matter, with a mass proportional to an exponential function of the quintessence field (hence realizing VAMP models within a String context). However, any attempt to saturate the present cold dark matter component in this manner leads to unacceptable deviations from cosmological data -a numerical study reveals that this source can account for up to about 7% of the total cold dark matter budget. We also show that (1) the model will support a de Sitter energy in agreement with observation at the expense of a miniscule breaking of supersymmetry in the compact space; (2) variations in the fine structure constant are controlled by the stabilized modulus and are negligible; (3) "fifth" forces are carried by the stabilized modulus and are short range; (4) the long time behavior of the model in four dimensions is that of a Robertson-Walker universe with a constant expansion rate (w = −1/3). Finally, we present a String theory background by lifting our six dimensional cosmological solution to ten dimensions.

Physical Review D

We introduce a very early universe model based on the thermodynamics of a gas of closed strings in a background that is nonperturbative in α 0. Upon considering the fully α 0-corrected equations extended to include certain anisotropic cosmological backgrounds, we describe the evolution of the system in three different stages parametrized by the gas's equation of state. Using standard string thermodynamical arguments, we start with an isotropic ten-dimensional universe inside the string scale and evolve it toward a universe with four large spacetime dimensions and six stabilized internal dimensions in the Einstein frame.