Abstract
We present a specific model for cosmological inflation driven by the Liouville field in a non-critical supersymmetric string framework, in which the departure from criticality is due to open strings stretched between two moving Type-II 5-branes. We use WMAP and other data on fluctuations in the cosmic microwave background to fix the parameters of the model, such as the relative separation and velocity of the 5-branes, respecting also the constraints imposed by data on light propagation from distant gamma-ray bursters. The model also suggests a small, relaxing component in the present vacuum energy that may accommodate the breaking of supersymmetry.
Highlights
An important consequence of this departure from critical string theory, and from the standard conformal invariance conditions used in [14], is the presence of an exponentially expanding inflationary phase for the four-dimensional cosmological scale factor
In non-critical string theory, such inflationary phases may be obtained [21] as a result of identifying the target time with the zero mode of the Liouville world-sheet σ-model field [18, 17]
We constrain the distance between the branes and the string coupling in this scenario, exhibiting a region of parameter space that is compatible with limits on deviations from naive Lorentz invariance in the propagation of high-energy photons from astrophysical sources such as gamma-ray bursters (GRBs) [23]–[25]
Summary
Before presenting our specific model, we first discuss briefly how an inflationary space-time may be derived generically as a consistent background in a non-critical string theory [21, 26]. Cosmically catastrophic non-critical string scenaria, such as that in [12], allow in general for a time-dependent deficit Q2(t) that relaxes to zero This may occur in such a way that, during the inflationary era Q2 is (for all practical purposes) constant, as in (1), eventually Q2 decreases with time so that, at the present era, one obtains compatibility with a new accelerating phase of the Universe. The Liouville dressing induces [16] σ-model terms of the form R(2)Qφ, where R(2) is the world-sheet curvature Such terms provide non-trivial contributions to the dilaton background in the (D + 1)-dimensional space-time (φ, t, Xi):. Corresponding to the conventional form of inflationary equations for scalar fields
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