Astrophysical constraints 
on compact objects in 4D Einstein-Gauss-Bonnet gravity

Charmousis, Christos; Lehébel, Antoine; Smyrniotis, Evangelos; Stergioulas, Nikolaos

doi:10.1088/1475-7516/2022/02/033

Cited by 37 publications

(28 citation statements)

References 127 publications

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“…We have included here a linear time dependence of the scalar field, which is possible for shift symmetric theories and was discussed in particular in [26] for 4dEGB black holes, but later we will assume q = 0. In the rest of this section, we discuss the axial and polar perturbations in general, before specialising our discussion to the specific cases of EsGB and 4dEGB black holes in the subsequent sections.…”

Section: First-order System For Horndeski Theoriesmentioning

confidence: 99%

Linear perturbations of Einstein-Gauss-Bonnet black holes

Langlois,

Noui,

Roussille

2022

Preprint

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We study linear perturbations about non rotating black hole solutions in scalar-tensor theories, more specifically Horndeski theories. We consider two particular theories that admit known hairy black hole solutions. The first one, Einstein-scalar-Gauss-Bonnet theory, contains a Gauss-Bonnet term coupled to a scalar field, and its black hole solution is given as a perturbative expansion in a small parameter that measures the deviation from general relativity. The second one, known as 4-dimensional-Einstein-Gauss-Bonnet theory, can be seen as a compactification of higher-dimensional Lovelock theories and admits an exact black hole solution. We study both axial and polar perturbations about these solutions and write their equations of motion as a first-order (radial) system of differential equations, which enables us to study the asymptotic behaviours of the perturbations at infinity and at the horizon following an algorithm we developed recently. For the axial perturbations, we also obtain effective Schrödinger-like equations with explicit expressions for the potentials and the propagation speeds. We see that while the Einstein-scalar-Gauss-Bonnet solution has well-behaved perturbations, the solution of the 4-dimensional-Einstein-Gauss-Bonnet theory exhibits unusual asymptotic behaviour of its perturbations near its horizon and at infinity, which makes the definition of ingoing and outgoing modes impossible. This indicates that the dynamics of these perturbations strongly differs from the general relativity case and seems pathological.

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Section: First-order System For Horndeski Theoriesmentioning

confidence: 99%

Linear perturbations of Einstein-Gauss-Bonnet black holes

Langlois,

Noui,

Roussille

2022

Preprint

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“…At the same time, it would be interesting to extend our considerations to other effective theories with matter fields -for example, involving a metric and a scalar. In this context, it is known that the Horndeski theory corresponding to the four-dimensional limit of Gauss-Bonnet gravity [61][62][63] allows for a Lense-Thirring metric characterized by the static metric function [64]. One may then wonder if this is the unique Horndeski theory with that property.…”

Section: Discussionmentioning

confidence: 99%

Generalized Lense--Thirring metrics: higher-curvature corrections and solutions with matter

Gray,

Hennigar,

Kubiznak

et al. 2021

Preprint

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The Lense-Thirring spacetime describes a 4-dimensional slowly rotating approximate solution of vacuum Einstein equations valid to a linear order in rotation parameter. It is fully characterized by a single metric function of the corresponding static (Schwarzschild) solution. In this paper, we introduce a generalization of the Lense-Thirring spacetimes to the higher-dimensional multiply-spinning case, with an ansatz that is not necessarily fully characterized by a single (static) metric function. This generalization lets us study slowly rotating spacetimes in various higher curvature gravities as well as in the presence of non-trivial matter. Moreover, the ansatz can be recast in Painlevé-Gullstrand form (and thence is manifestly regular on the horizon) and admits a tower of exact rank-2 and higher rank Killing tensors that rapidly grows with the number of dimensions. In particular, we construct slowly multiply-spinning solutions in Lovelock gravity and notably show that in four dimensions Einstein gravity is the only non-trivial theory amongst all up to quartic curvature gravities that admits a Lense-Thirring solution characterized by a single metric function.

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“…However, slowlyrotating solutions can be constructed, as was done originally in Ref. [209] for the scalartensor theory of Section 2.3. Treating rotation as a perturbation to the static solutions, we follow the Hartle-Thorne formalism [259,260].…”

Section: Slowly Rotating Solutionsmentioning

confidence: 99%

“…Upper bounds on α obtained with this method are given in Table 1 (see Refs. [208,209] for details) + .…”

Section: Constraints On αmentioning

confidence: 99%

The 4D Einstein-Gauss-Bonnet Theory of Gravity: A Review

Fernandes,

Carrilho,

Clifton

et al. 2022

Preprint

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We review the topic of 4D Einstein-Gauss-Bonnet gravity, which has been the subject of considerable interest over the past two years. Our review begins with a general introduction to Lovelock's theorem, and the subject of Gauss-Bonnet terms in the action for gravity. These areas are of fundamental importance for understanding modified theories of gravity, and inform our subsequent discussion of recent attempts to include the effects of a Gauss-Bonnet term in four space-time dimensions by rescaling the appropriate coupling parameter. We discuss the mathematical complexities involved in implementing this idea, and review recent attempts at constructing welldefined, self-consistent theories that enact it. We then move on to consider the gravitational physics that results from these theories, in the context of black holes, cosmology, and weak-field gravity. We show that 4D Einstein-Gauss-Bonnet gravity exhibits a number of interesting phenomena in each of these areas.

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Astrophysical constraints on compact objects in 4D Einstein-Gauss-Bonnet gravity

Cited by 37 publications

References 127 publications

Linear perturbations of Einstein-Gauss-Bonnet black holes

Linear perturbations of Einstein-Gauss-Bonnet black holes

Generalized Lense--Thirring metrics: higher-curvature corrections and solutions with matter

The 4D Einstein-Gauss-Bonnet Theory of Gravity: A Review

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