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arXiv · hep-th/0512209

Falsifying Tree Level String Motivated Bouncing Cosmologies

C. P. Constantinidis·J. C. Fabris·R. G. Furtado·N. Pinto-Neto·D. Gonzalez
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Abstract

The string effective action at tree level contains, in its bosonic sector, the Einstein-Hilbert term, the dilaton, and the axion, besides scalar and gauge fields coming from the Ramond-Ramond sector. The reduction to four dimensions brings to scene moduli fields. We generalize this effective action by introducing two arbitrary parameters, $ω$ and $m$, connected with the dilaton and axion couplings. In this way, more general frameworks can be analyzed. Regular solutions with a bounce can be obtained for a range of (negative) values of the parameter $ω$ which, however, exclude the pure string configuration ($ω= - 1$). We study the evolution of scalar perturbations in such cosmological scenarios. The predicted primordial power spectrum decreases with the wavenumber with spectral index $n_s=-2$, in contradiction with the results of the $WMAP$. Hence, all such effective string motivated cosmological bouncing models seem to be ruled out, at least at the tree level approximation.

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C. P. Constantinidis, J. C. Fabris, R. G. Furtado, N. Pinto-Neto, D. Gonzalez. 2005-12-16. Falsifying Tree Level String Motivated Bouncing Cosmologies. https://doi.org/10.1103/physrevd.73.123513

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