Kinetic coupling corrected Einstein–Gauss–Bonnet gravity late-time phenomenology

De Sitter solutions play an important role in cosmology because the knowledge of unstable de Sitter solutions can be useful to describe inflation, whereas stable de Sitter solutions are often used in models of late-time acceleration of the Universe. The Einstein–Gauss–Bonnet gravity cosmological models are actively used both as inflationary models and as dark energy models. To modify the Einstein equations one can add a nonlinear function of the Gauss–Bonnet term or a function of the scalar field multiplied on the Gauss–Bonnet term. The effective potential method essentially simplifies the search and stability analysis of de Sitter solutions, because the stable de Sitter solutions correspond to minima of the effective potential.

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DARK ENERGY FROM SCALAR FIELD WITH GAUSS–BONNET AND NON-MINIMAL KINETIC COUPLING

Modern Physics Letters A ◽

10.1142/s0217732312500186 ◽

2012 ◽

Vol 27 (04) ◽

pp. 1250018 ◽

Cited By ~ 33

Author(s):

L. N. GRANDA

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Power Law ◽

Dynamical Equation ◽

Early Time ◽

Scalar Fields ◽

Late Time ◽

Kinetic Coupling ◽

Energy Behavior ◽

Phantom Phase

We consider a model of scalar field with non-minimal kinetic couplings to the curvature, and additional coupling to the Gauss–Bonnet four-dimensional invariant. The model presents rich cosmological dynamics and some of its solutions are analyzed. A variety of scalar fields and potentials giving rise to power-law expansion have been found. Two solutions with dynamical equation of state are considered. The first solution unifies early time power-law behavior with late time cosmological constant dominance. The second solution is able to describe a universe in the phantom phase, and depending on the parameters may describe essentially dark energy behavior, or may contain the decelerated and accelerated phases.

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Some late-time cosmological aspects of a Gauss–Bonnet gravity with nonminimal coupling à la Brans–Dicke: solutions and perspectives

Canadian Journal of Physics ◽

10.1139/cjp-2012-0366 ◽

2013 ◽

Vol 91 (4) ◽

pp. 300-321 ◽

Cited By ~ 8

Author(s):

Rami Ahmad El-Nabulsi

Keyword(s):

Scalar Field ◽

String Theory ◽

Modified Gravity ◽

Cosmological Models ◽

Gravity Theory ◽

Accelerating Universe ◽

Late Time ◽

Nonminimal Coupling ◽

Bonnet Gravity ◽

Time Dynamics

In this paper, we study modified homogeneous and isotropic cosmological models based on the Gauss–Bonnet invariant term as models of an accelerating universe. We discuss and criticize the late-time dynamics of six independent cosmological models: in the first model, we discuss the case of the modified gravity f(R) ∝ R1+δ for δ = −1/2 and 1 augmented by the Gauss–Bonnet invariant term; in the second model, we discuss the general case of f(R) ∝ R1+δ accompanied by a nonminimal coupling between the scalar field and the Ricci curvature as well as the Gauss–Bonnet invariant; in the third model, we discuss a generalized modified gravity model that includes the Einstein–Hilbert action, a dynamical cosmological constant, and an effective gravitational coupling constant; in the fourth model, we discuss a more generalized modified scalar–tensor cosmology that includes in addition to the Gauss–Bonnet invariant term, stringy corrections motivated from string and heterotic superstring arguments; in the fifth model, we discuss the cosmological dynamics of a nonminimal scalar Gauss–Bonnet gravity theory motivated from string theory; and finally in the sixth model, we discuss the possibility of having an extension of the generalized modified gravity theory, free from nonminimal coupling with δ = 0, with a Hubble expansion rate and an equation of state parameter that depend on the Gauss–Bonnet invariant term. In the first five models, we conjecture that the Hubble parameter is related to the scalar field by the relation [Formula: see text], which is applied merely to the late time epoch. This ansatz is in fact motivated by some recent advances in scalar–tensor theory and string theory. All of the six models reveal interesting consequences, which are discussed in some detail. Our main objective in this work is to analyze, criticize, and differentiate between viable realistic models and those that are not. Many critical points are discussed in some detail.

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Out of the swampland with multifield quintessence?

Journal of High Energy Physics ◽

10.1007/jhep10(2020)035 ◽

2020 ◽

Vol 2020 (10) ◽

Author(s):

Michele Cicoli ◽

Giuseppe Dibitetto ◽

Francisco G. Pedro

Keyword(s):

Initial Conditions ◽

Functional Dependence ◽

Scalar Potential ◽

Scalar Fields ◽

Cosmic Acceleration ◽

Late Time ◽

Kinetic Coupling ◽

Current State ◽

The Stability ◽

Promising Avenue

Abstract Multifield models with a curved field space have already been shown to be able to provide viable quintessence models for steep potentials that satisfy swampland bounds. The simplest dynamical systems of this type are obtained by coupling Einstein gravity to two scalar fields with a curved field space. In this paper we study the stability properties of the non-trivial fixed points of this dynamical system for a general functional dependence of the kinetic coupling function and the scalar potential. We find the existence of non-geodesic trajectories with a sharp turning rate in field space which can give rise to late-time cosmic acceleration with no need for flat potentials. In particular, we discuss the properties of the phase diagram of the system and the corresponding time evolution when varying the functional dependence of the kinetic coupling. Interestingly, upon properly tuning the initial conditions of the field values, we find trajectories that can describe the current state of the universe. This could represent a promising avenue to build viable quintessence models out of the swampland if they could be consistently embedded in explicit string constructions.

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Gravitational lensing in 4-D Einstein–Gauss–Bonnet gravity in the presence of plasma

Physics of the Dark Universe ◽

10.1016/j.dark.2021.100798 ◽

2021 ◽

Vol 32 ◽

pp. 100798

Author(s):

Gulmina Zaman Babar ◽

Farruh Atamurotov ◽

Abdullah Zaman Babar

Keyword(s):

Gravitational Lensing ◽

Bonnet Gravity

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Quantum extremal islands made easy. Part III. Complexity on the brane

Journal of High Energy Physics ◽

10.1007/jhep02(2021)173 ◽

2021 ◽

Vol 2021 (2) ◽

Cited By ~ 3

Author(s):

Juan Hernandez ◽

Robert C. Myers ◽

Shan-Ming Ruan

Keyword(s):

Holographic Model ◽

Bonnet Gravity ◽

Higher Curvature Gravity ◽

Theories Of Gravity

Abstract We examine holographic complexity in the doubly holographic model introduced in [1, 2] to study quantum extremal islands. We focus on the holographic complexity=volume (CV) proposal for boundary subregions in the island phase. Exploiting the Fefferman-Graham expansion of the metric and other geometric quantities near the brane, we derive the leading contributions to the complexity and interpret these in terms of the generalized volume of the island derived from the induced higher-curvature gravity action on the brane. Motivated by these results, we propose a generalization of the CV proposal for higher curvature theories of gravity. Further, we provide two consistency checks of our proposal by studying Gauss-Bonnet gravity and f(ℛ) gravity in the bulk.

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Unitarity at the late time boundary of de Sitter

Journal of High Energy Physics ◽

10.1007/jhep06(2020)041 ◽

2020 ◽

Vol 2020 (6) ◽

Cited By ~ 1

Author(s):

Gizem Şengör ◽

Constantinos Skordis

Keyword(s):

Late Time ◽

De Sitter ◽

Time Boundary

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Ionized AGN outflows are less powerful than assumed: A multi-wavelength census of outflows in type II AGN

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320002975 ◽

2019 ◽

Vol 15 (S356) ◽

pp. 225-225

Author(s):

Dalya Baron

Keyword(s):

Optical Emission ◽

Infrared Emission ◽

Type Ii ◽

Ionized Gas ◽

Kinetic Coupling ◽

Mass Outflow ◽

Multi Wavelength ◽

Novel Method ◽

First Time ◽

Ionization Parameter

AbstractIn this talk I will show that multi-wavelength observations can provide novel constraints on the properties of ionized gas outflows in AGN. I will present evidence that the infrared emission in active galaxies includes a contribution from dust which is mixed with the outflow and is heated by the AGN. We detect this infrared component in thousands of AGN for the first time, and use it to constrain the outflow location. By combining this with optical emission lines, we constrain the mass outflow rates and energetics in a sample of 234 type II AGN, the largest such sample to date. The key ingredient of our new outflow measurements is a novel method to estimate the electron density using the ionization parameter and location of the flow. The inferred electron densities, ∼104.5 cm−3, are two orders of magnitude larger than found in most other cases of ionized outflows. We argue that the discrepancy is due to the fact that the commonly-used [SII]-based method underestimates the true density by a large factor. As a result, the inferred mass outflow rates and kinetic coupling efficiencies are 1–2 orders of magnitude lower than previous estimates, and 3–4 orders of magnitude lower than the typical requirement in hydrodynamic cosmological simulations. These results have significant implications for the relative importance of ionized outflows feedback in this population.

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DARK ENERGY, WITH SIGNATURES

International Journal of Modern Physics D ◽

10.1142/s0218271810018372 ◽

2010 ◽

Vol 19 (14) ◽

pp. 2325-2330

Author(s):

SOURISH DUTTA ◽

ROBERT J. SCHERRER ◽

STEPHEN D. H. HSU

Keyword(s):

Dark Energy ◽

Equation Of State ◽

Energy Scale ◽

Fine Tuning ◽

Time Dependent ◽

Late Time ◽

Particle Content ◽

Energy Field ◽

Energy Models ◽

New Energy

We propose a class of simple dark energy models which predict a late-time dark radiation component and a distinctive time-dependent equation of state w(z) for redshift z < 3. The dark energy field can be coupled strongly enough to standard model particles to be detected in colliders, and the model requires only modest additional particle content and little or no fine-tuning other than a new energy scale of order milli-electron volts.

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