Abstract
We consider a time-dependent bosonic string in graviton, dilaton and tachyon backgrounds, for which it was already shown that conformal invariance is respected to all orders in α′ and in any space–time dimension. Assuming that the tachyon is off-shell, we show in this note that the specific time-homogeneity of the corresponding space–time effective action leads to a power-law expanding Universe, that can be interpreted as dark energy. We arrive at this result without requiring the knowledge of the structure of the string effective action, which is not known to all orders in α′. Moreover, in our approach, the background configurations are consistent in a four-dimensional space–time, without any need for extra dimensions.
Highlights
Introduction and SummaryOne of the most important experimental discoveries of the past decade is the fact that at the current era our Universe is accelerating
In the context of a homogeneous and isotropic Friedmann-Robertson-Walker (FRW) Cosmology, the de-Sitter model, in its simplest version, can match a plethora of astrophysical observations, ranging from galactic and super-galactic cluster dynamics to Cosmic Microwave Background temperature fluctuations, provided there is a sufficient amount of cold dark matter
In a first quantized string framework, in which the dynamics of strings propagating in certain non-trivial space-time backgrounds is described by appropriate world-sheet σ-models, the role of local conformal invariance on the world-sheet of the string is essential to leave space time Physics unaffected
Summary
One of the most important experimental discoveries of the past decade is the fact that at the current era our Universe is accelerating. The homogeneity in time of the various terms in the expressions of the world-sheet Weyl-anomaly coefficients guarantees the existence of a given renormalization scheme in which the β-functions vanish In this sense, the corresponding backgrounds are interpreted as classical on-shell solutions of equations of motion obtained from an effective action, whose form cannot be known explicitly, due to the complicated structure of the various terms (infinite in order of derivatives). We demonstrate how their inclusion leads to dark energy, again independently of the form of the target-space effective action. We remind here that the dilaton (4) and scale factor (5) are not solutions of equations of motion obtained by varying a space time effective action, but are given by the homogeneity of β-functions, to all orders in α′
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