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

Guo, Zong Kuan; Ohta, Nobuyoshi; Tsujikawa, Shinji

doi:10.1103/physrevd.75.023520

Cited by 48 publications

(48 citation statements)

References 79 publications

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“…If β = 0 and 0 < γ < 1, it was shown that the tensor perturbations suffer from instabilities on small scales, because c 2 T = 2γ − 5 is negative [10]. This type of instabilities has been also found in Refs.…”

Section: Power-law Inflationmentioning

confidence: 61%

“…In the case β = 0 (no potential), we choose ω = −1 and γ = γ − , since γ + > 1. The condition for inflation requires α < 1/4 [10]. Taking the positive sign of φ, we obtain…”

Section: Power-law Inflationmentioning

confidence: 99%

“…A model in which inflation is driven by the GB term and a higher-order kinetic energy term was studied. When the GB term dominates the dynamics of the background, tensor perturbations exhibit violent negative instabilities around a de Sitter background on * Electronic address: guozk@physik.uni-bielefeld.de † Electronic address: dschwarz@physik.uni-bielefeld.de small scales, in spite of the fact that scale-invariant scalar perturbations can be achieved [10]. Besides the kinetic and GB terms, a scalar potential arises naturally from supersymmetry breaking or other non-perturbative effects.…”

Section: Introductionmentioning

confidence: 99%

“…Recently it has been shown that the GB term might give rise to violent instabilities of tensor perturbations [10]. A model in which inflation is driven by the GB term and a higher-order kinetic energy term was studied.…”

Section: Introductionmentioning

confidence: 99%

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Power spectra from an inflaton coupled to the Gauss-Bonnet term

2009

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We consider power-law inflation with a Gauss-Bonnet correction inspired by string theory. We analyze the stability of cosmological perturbations and obtain the allowed parameter space. We find that for GB-dominated inflation ultra-violet instabilities of either scalar or tensor perturbations show up on small scales. The Gauss-Bonnet correction with a positive (or negative) coupling may lead to a reduction (or enhancement) of the tensor-to-scalar ratio in the potential-dominated case. We place tight constraints on the model parameters by making use of the WMAP 5-year data.

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Section: Power-law Inflationmentioning

confidence: 61%

“…In the case β = 0 (no potential), we choose ω = −1 and γ = γ − , since γ + > 1. The condition for inflation requires α < 1/4 [10]. Taking the positive sign of φ, we obtain…”

Section: Power-law Inflationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Power spectra from an inflaton coupled to the Gauss-Bonnet term

2009

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“…The model buildings of inflation in string theory has been widely investigated, e.g., [11][12][13][14] and [15,16] for recent reviews. The inflationary GWs is a powerful tool to probe the physics beyond GR, since it is only affected by the physics relevant to gravity, e.g., the change of the propagating speed of GWs [17].…”

Section: Jhep02(2016)059mentioning

confidence: 99%

Oscillation in power spectrum of primordial gravitational wave as a signature of higher-order stringy corrections

Cai

Wang

Piao

2016

J. High Energ. Phys.

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In low-energy effective string theory, α corrections involve the coupling of the dilaton field to Gauss-Bonnet term. We assume that the dilaton potential is fine tuned so that the dilaton field may oscillate rapidly for a while around the minimum of its potential but the inflation background is not affected. By numerical method, we find that if the dilaton starts to oscillate at the time of about ∼ 60 e-folds before the end of inflation, α correction may bring unusual oscillations to the inflationary gravitational wave spectrum, which might be measurably imprinted in the CMB B-mode polarization.

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Modified Gravity Models of Dark Energy

Tsujikawa¹

2010

Lecture Notes in Physics

319

196

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We review recent progress of modified gravity models of dark energy-based on f (R) gravity, scalar-tensor theories, braneworld gravity, Galileon gravity, and other theories. In f (R) gravity it is possible to design viable models consistent with local gravity constraints under a chameleon mechanism, while satisfying conditions for the cosmological viability. We also construct a class of scalar-tensor dark energy models based on Brans-Dicke theory in the presence of a scalar-field potential with a large coupling strength Q between the field and non-relativistic matter in the Einstein frame. We study the evolution of matter density perturbations in f (R) and Brans-Dicke theories to place observational constraints on model parameters from the power spectra of galaxy clustering and Cosmic Microwave Background (CMB).The Dvali-Gabadazde-Porrati braneworld model can be compatible with local gravity constraints through a nonlinear field self-interaction φ(∂µφ∂ µ φ) arising from a brane-bending mode, but the self-accelerating solution contains a ghost mode in addition to the tension with the combined data analysis of Supernovae Ia (SN Ia) and Baryon Acoustic Oscillations (BAO). The extension of the field self-interaction to more general forms satisfying the Galilean symmetry ∂µφ → ∂µφ + bµ in the flat space-time allows a possibility to avoid the appearance of ghosts and instabilities, while the late-time cosmic acceleration can be realized by the field kinetic energy. We study observational constraints on such Galileon models by using the data of SN Ia, BAO, and CMB shift parameters.We also briefly review other modified gravitational models of dark energy-such as those based on Gauss-Bonnet gravity and Lorentz-violating theories. Contents

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

Cited by 48 publications

References 79 publications

Power spectra from an inflaton coupled to the Gauss-Bonnet term

Power spectra from an inflaton coupled to the Gauss-Bonnet term

Oscillation in power spectrum of primordial gravitational wave as a signature of higher-order stringy corrections

Modified Gravity Models of Dark Energy

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