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Phys. Rev. D 75, 023520 (2007) [13 pages]

Realizing scale-invariant density perturbations in low-energy effective string theory

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Zong-Kuan Guo,¹ Nobuyoshi Ohta,¹ and Shinji Tsujikawa²
¹Department of Physics, Kinki University, Higashi-Osaka, Osaka 577-8502, Japan
²Department of Physics, Gunma National College of Technology, Gunma 371-8530, Japan

Received 31 October 2006; published 23 January 2007

Wediscuss the realization of inflation and resulting cosmological perturbations inthe low-energy effective string theory. In order to obtain nearlyscale-invariant spectra of density perturbations and a suppressed tensor-to-scalar ratio,it is generally necessary that the dilaton field phi iseffectively decoupled from gravity together with the existence of aslowly varying dilaton potential. We also study the effect ofsecond-order corrections to the tree-level action which are the sumof a Gauss-Bonnet term coupled to phi and a kineticterm ([del]phi)⁴. We find that it is possible to realizeobservationally supported spectra of scalar and tensor perturbations provided thatthe correction is dominated by the ([del]phi)⁴ term even inthe absence of the dilaton potential. When the Gauss-Bonnet termis dominant, tensor perturbations exhibit violent negative instabilities on smallscales about a de Sitter background in spite of thefact that scale-invariant scalar perturbations can be achieved.

©2007 The American Physical Society

URL:	http://link.aps.org/doi/10.1103/PhysRevD.75.023520
DOI:	10.1103/PhysRevD.75.023520
PACS:	98.80.Cq; 04.62.+v; 98.80.Jk 98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.) 04.62.+v Quantum field theory in curved spacetime 98.80.Jk Mathematical and relativistic aspects of cosmology YEAR: 2007
KEYWORDS:	string theory, gravitation, cosmology, cosmic acceleration

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