Falsifying Tree Level String Motivated Bouncing Cosmologies

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, $\omega$ 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.

Latex file, 19 pages, 3 figures in eps format

References in corpus (29)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Preliminary Maps and Basic Results
• Cosmological parameters from SDSS and WMAP
• The Pre-Big Bang Scenario in String Cosmology
• On the Generation of a Scale-Invariant Spectrum of Adiabatic Fluctuations in Cosmological Models with a Contracting Phase
• Cosmology and Brane Worlds: A Review
• Primordial perturbations in a non singular bouncing universe model
• Cosmological perturbations through a simple bounce
• Detecting extra dimensions with gravity wave spectroscopy: the black string brane-world
• Passing through the bounce in the ekpyrotic models
• Perturbations in a non-singular bouncing Universe
• On Brane World Cosmological Perturbations
• Cosmological perturbations in the bulk and on the brane
• Primordial fluctuations and cosmological inflation after WMAP 1.0
• Cosmological perturbations and the transition from contraction to expansion
• On the "Causality Argument" in Bouncing Cosmologies
• The Cosmology of Massless String Modes
• Relaxing to Three Dimensions
• Study of a Class of Four Dimensional Nonsingular Cosmological Bounces
• Has the Universe always expanded ?
• Regular two-component bouncing cosmologies and perturbations therein
• Regular cosmological solutions in low energy effective action from string theories
• Adiabatic and entropy perturbations propagation in a bouncing Universe
• Construction of nonsingular cosmological solutions in string theories
• General solution for scalar perturbations in bouncing cosmologies
• A Note on Perturbations During a Regular Bounce
• Nonsingular multidimensional cosmologies without fine tuning
• Inflation after WMAP3
• Understanding selection effects in observed samples of cataclysmic variables
• A post-WMAP perspective on inflation

Cited by in corpus (1)

• Bouncing solutions in Rastall's theory with a barotropic fluid