arXiv subjects

Y. Brihaye

Publications and source records attributed to Y. Brihaye.

At least 37 records · Page 2Linked to original sources

arXiv2016

Boson stars, neutron stars and black holes in five dimensions

Different types of gravitating compact objects occuring in d=5 space-time are considered: boson stars, hairy black holes and perfect fluid solutions. All these solutions of the Einstein equations coupled to matter have well established counterparts in d=4; in particular neutron stars can be modell§ed more or less realistically by a perfect fluid. A special emphasis is set on the possibility -and/or the necessity- for these solutions to have an intrinsic angular momentum or spin. The influence of a cosmological constant on their pattern is also studied. Several physical properties are presented from which common features to boson and neutron stars clearly emerge. We finally point out qualitative differences of the gravitational interaction supporting these classical lumps between four and five dimensions.

gr-qc↗

arXiv2015

Black Holes with Scalar Hairs in Einstein-Gauss-Bonnet Gravity

The Einstein-Gauss-Bonnet gravity in five dimensions is extended by scalar fields and the corresponding equations are reduced to a system of non-linear differential equations. A large family of regular solutions of these equations is shown to exist. Generically, these solutions are spinning black holes with scalar hairs. They can be characterized (but not uniquely) by an horizon and an angular velocity on this horizon. Taking particular limits the black holes approach boson star or become extremal, in any case the limiting configurations remain hairy.

gr-qc↗

arXiv2014

Self-Gravitating Spherical Solutions of the non-minimally coupled non-Abelian Higgs Model

Motivated by the Higgs Inflation scenario, we study static spherically-symmetric solutions of the non-Abelian Higgs model coupled non-minimally to Gravity. We find solutions for the self-gravitating sphaleron as well as monopole-like solutions and study the impact of the non-minimal coupling on their properties. Finally we discuss shortly the possibility that these solutions interact gravitationally with star-like objects like boson stars.

gr-qc↗

arXiv2014

Dirac equation for sphercially symmetric $AdS_5$ space-time and application to a boson star in EGB gravity

We discuss the Dirac equation in a curved 5-dimensional spherically symmetric space-time. The angular part of the solutions is thoroughly studied, in a formulation suited for extending to rotating space-times with equal angular momenta. It has a symmetry $SU(2)\times U(1)$ and is implemented by the Wigner functions. The radial part forms a Dirac-Schrödinger type equation, and existence of the analytical solutions of the massless and the massive modes is confirmed. The solutions are described by the Jacobi polynomials. Also, the spinor of the both large and small components is obtained numerically. As a direct application of our formulation, we evaluate the spectrum of the Dirac fermion in Einstein-Gauss-Bonnet space-time and the space-time of a boson star.

gr-qc↗

arXiv2013

Dynamics on the cone: closed orbits and superintegrability

The generalization of Bertrand's theorem to the case of the motion of point particle on the surface of a cone is presented. The superintegrability of such models is discussed. The additional integrals of motion are analyzed for the case of Kepler and harmonic oscillator potentials.

math-ph↗

arXiv2013

Gravitating Q-tubes and cylindrical spacetime

We consider a model involving a self-interacting complex scalar field minimally coupled to gravity and emphasize the cylindrically symmetric classical solutions. A general ansatz is performed which transforms the field equations into a system of differential equations. In the generic case, the scalar field depends on the four space-time coordinates. The underlying Einstein vacuum equations are worth studying by themselve and lead to numerous analytic results extending the Kasner solutions. The solutions of the coupled system are -static as well as stationnary- gravitating Q-tubes of scalar matter which deform space-time.

gr-qc↗

arXiv2012

Perfect Fluid Spherically-Symmetric Solutions in Massive Gravity

We study spherically-symmetric solutions in Massive Gravity generated by matter sources with polytropic equation of state. We concentrate in the non-perturbative regime where the mass term non-linearities are important, and present the main features of the solutions.

gr-qc↗

arXiv2012

A scalar field instability of rotating and charged black holes in (4+1)-dimensional Anti-de Sitter space-time

We study the stability of static as well as of rotating and charged black holes in (4+1)-dimensional Anti-de Sitter space-time which possess spherical horizon topology. We observe a non-linear instability related to the condensation of a charged, tachyonic scalar field and construct "hairy" black hole solutions of the full system of coupled Einstein, Maxwell and scalar field equations. We observe that the limiting solution for small horizon radius is either a hairy soliton solution or a singular solution that is not a regular extremal solution. Within the context of the gauge/gravity duality the condensation of the scalar field describes a holographic conductor/superconductor phase transition on the surface of a sphere.

hep-th↗

arXiv2011

Charged, rotating black holes in Einstein-Gauss-Bonnet gravity

We consider the Einstein-Gauss-Bonnet equations in five dimensions including a negative cosmological constant and a Maxwell field. Using an appropriate Ansatz for the metric and for the electromagnetic fields, we construct numerically black holes with two equal angular momenta in the two orthogonal space-like planes of space-time. Families of such solutions, labeled by the angular momentum and by the electric charge are obtained for many representative intervals of the Gauss-Bonnet coupling constant $α$. It is argued that, for fixed values of $α$, the solutions terminate into extremal black holes at ($α$-dependent) critical values of the angular momentum and/or of the electric charge. The influence of the Gauss-Bonnet coupling constant, of the charge and of the cosmological constant on the thermodynamics of the black holes and on their domain of existence is analyzed.

gr-qc↗

arXiv2011

Exact String-Like Solutions in Conformal Gravity

The cylindrically-symmetric static vacuum equations of Conformal Gravity are solved for the case of additional boost symmetry along the axis. We present the complete family of solutions which describe the exterior gravitational field of line sources in Conformal Gravity. We also analyze the null geodesics in these spaces.

gr-qc↗

arXiv2010

Cylindrically-Symmetric Solutions in Conformal Gravity

Cylindrically-symmetric solutions in Conformal Gravity are investigated and several new solutions are presented and discussed. Among them, a family of vacuum solutions, generalizations of the Melvin solution and cosmic strings of the Abelian Higgs model. The Melvin-like solutions have finite energy per unit length, while the string-like solutions do not.

gr-qc↗

arXiv2010

Einstein-Gauss-Bonnet black strings

We construct uniform black-string solutions in Einstein-Gauss-Bonnet gravity for all dimensions $d$ between five and ten and discuss their basic properties. Closed form solutions are found by taking the Gauss-Bonnet term as a perturbation from pure Einstein gravity. Nonperturbative solutions are constructed by solving numerically the equations of the model. The Gregory-Laflamme instability of the black strings is explored via linearized perturbation theory. Our results indicate that new qualitative features occur for $d=6$, in which case stable configurations exist for large enough values of the Gauss-Bonnet coupling constant. For other dimensions, the black strings are dynamically unstable and have also a negative specific heat. We argue that this provides an explicit realization of the Gubser-Mitra conjecture, which links local dynamical and thermodynamic stability. Nonuniform black strings in Einstein-Gauss-Bonnet theory are also constructed in six spacetime dimensions.

hep-th↗

arXiv2010

Spherical Non-Abelian Solutions in Conformal Gravity

We study static spherically-symmetric solutions of non-Abelian gauge theory coupled to Conformal Gravity. We find solutions for the self-gravitating pure Yang-Mills case as well as monopole-like solutions of the Higgs system. The former are localized enough to have finite mass and approach asymptotically the vacuum geometry of Conformal Gravity, while the latter do not decay fast enough to have analogous properties.

gr-qc↗

arXiv2009

Spherical Structures in Conformal Gravity and its Scalar-Tensor Extension

We study spherically-symmetric structures in Conformal Gravity and in a scalar-tensor extension and gain some more insight about these gravitational theories. In both cases we analyze solutions in two systems: perfect fluid solutions and boson stars of a self-interacting complex scalar field. In the purely tensorial (original) theory we find in a certain domain of parameter space finite mass solutions with a linear gravitational potential but without a Newtonian contribution. The scalar-tensor theory exhibits a very rich structure of solutions whose main properties are discussed. Among them, solutions with a finite radial extension, open solutions with a linear potential and logarithmic modifications and also a (scalar-tensor) gravitational soliton. This may also be viewed as a static self-gravitating boson star in purely tensorial Conformal Gravity.

gr-qc↗

arXiv2009

Charged-spinning-gravitating Q-balls

We consider the lagrangian of a self-interacting complex scalar field admitting generically Q-balls solutions. This model is extended by minimal coupling to electromagnetism and to gravity. A stationnary, axially-symmetric ansatz for the different fields is used in order to reduce the classical equations. The system of non-linear partial differential equations obtained becomes a boundary value problem by supplementing a suitable set of boundary conditions. We obtain numerical evidences that the angular excitations of uncharged Q-balls, which exist in flat space-time, get continuously deformed by the Maxwell and the Einstein terms. The electromagnetic and gravitating properties of several solutions, including the spinning Q-balls, are emphasized.

gr-qc↗

arXiv2009

Einstein-Gauss-Bonnet black holes in de Sitter spacetime and the quasilocal formalism

We propose to compute the action and global charges of the asymptotically de Sitter solutions in Einstein-Gauss-Bonnet theory by using the counterterms method in conjunction with the quasilocal formalism. The general expression of the counterterms and the boundary stress tensor is presented for spacetimes of dimension $d\leq 7$. We apply this tehnique for several different solutions in Einstein-Gauss-Bonnet theory with a positive cosmological constant. Apart from known solutions, we consider also $d=5$ vacuum rotating black holes with equal magnitude angular momenta.

gr-qc↗

arXiv2008

Charged-Rotating Black Holes in Higher-dimensional (A)DS-Gravity

We present numerical evidences for the existence of rotating black hole solutions in d-dimensional Einstein-Maxwell theory with a cosmological constant and for $d$ odd. The metric used possesses $(d+1)/2$ Killing vectors and the solutions have $(d-1)/2$ equal angular momenta. A Schwarschild-type coordinate is used for the radial variable and both signs of the cosmological constant are emphasized. Several properties of the solutions are studied, namely their surface gravity, mass and angular momentum as functions of two parameters: the magnetic field and the angular velocity at the horizon. The influence of the electromagnetic field on the domain of existence of the black holes is studied are compared to the vacuum case where analytic solutions are available.

gr-qc↗

arXiv2008

Superconducting and Spinning Non-Abelian Flux Tubes

We find new non-Abelian flux tube solutions in a model of $N_f$ scalar fields in the fundamental representation of SU(N)xU(1) with $N \leq N_f$ (the ``extended non-Abelian Higgs model''), and study their main properties. Among the solutions there are spinning strings as well as superconducting ones. The solutions exist only in a non trivial domain of the parameter space defined by the ratio between the SU(N) and U(1) coupling constants, the scalar self-interaction coupling constants, the magnetic fluxes (Abelian as well as non-Abelian) and the ``twist parameter'' which is a non-trivial relative phase of the Higgs fields.

hep-th↗