Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
2005-12-16
Phys.Rev.D73:123513,2006
Physics
High Energy Physics
High Energy Physics - Theory
Latex file, 19 pages, 3 figures in eps format
Scientific paper
10.1103/PhysRevD.73.123513
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, $\omega$ 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 $\omega$ which, however, exclude the pure string configuration ($\omega = - 1$). 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.
Constantinidis Clisthenis P.
Fabris Julio Cesar
Furtado R. G.
Gonzalez Dania
Pinto-Neto Nelson
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