arXiv subjects

Y. Brihaye

Publications and source records attributed to Y. Brihaye.

At least 19 recordsLinked to original sources

arXiv2024

Q-balls and charged Q-balls in a two-scalar field theory with generalized Henon-Heiles potential

We construct Q-ball solutions from a model consisting of one massive scalar field $ξ$ and one massive complex scalar field $ϕ$ interacting via the cubic couplings $g_1 ξϕ^{*} ϕ+ g_2 ξ^3$, typical of Henon-Heiles-like potentials. Although being formally simple, these couplings allow for Q-balls. In one spatial dimension, analytical solutions exist, either with vanishing or non vanishing $ϕ$. In three spatial dimensions, we numerically build Q-ball solutions and investigate their behaviours when changing the relatives values of $g_1$ and $g_2$. For $g_1 g_2$. We then extend the former solutions by gauging the U(1)-symmetry of $ϕ$ and show that charged Q-balls exist.

hep-th↗

arXiv2022

$Z_N$-balls: Solitons from $Z_N$-symmetric scalar field theory

We discuss the conditions under which static, finite-energy, configurations of a complex scalar field $ϕ$ with constant phase and spherically symmetric norm exist in a potential of the form $V(ϕ^*ϕ, ϕ^N+ϕ^{*N})$ with $N\in\mathbb{N}$ and $N\geq2$, i.e. a potential with a $Z_N$-symmetry. Such configurations are called $Z_N$-balls. We build explicit solutions in $(3+1)$-dimensions from a model mimicking effective field theories based on the Polyakov loop in finite-temperature SU($N$) Yang-Mills theory. We find $Z_N$-balls for $N=$3, 4, 6, 8, 10 and show that only static solutions with zero radial node exist for $N$ odd, while solutions with radial nodes may exist for $N$ even.

hep-th↗

arXiv2022

Charged and radially excited boson stars (in Anti-de Sitter)

We study charged and radially excited boson stars in both asymptotically flat as well as asymptotically Anti-de Sitter space-time. We demonstrate that two different types of radially excited solutions exist~: one that persists in the linear limit of small scalar fields, in which analytical arguments suggest the existence of these solutions, and one that appears only in the highly non-linear regime of the model. We also demonstrate that the formation of wavy scalar hair discussed previously for black holes and boson stars in asymptotically flat space-time persists for asymptotically Anti-de Sitter space-time.

gr-qc↗

arXiv2022

Boson and neutron stars with increased density

We discuss boson stars and neutron stars, respectively, in a scalar-tensor gravity model with an explicitly time-dependent real scalar field. While the boson stars in our model -- in contrast to the neutron stars -- do not possess a hard core, we find that the qualitative effects of the formation of scalar hair are similar in both cases : the presence of the gravity scalar allows both type of stars to exist for larger central density as well as larger mass at given radius than their General Relativity counterparts. In particular, we find new types of neutron stars with scalar hair which have radii very close to the corresponding Schwarzschild radius and hence are comparable in density to black holes. This new branch of solutions is stable with respect to the decay into individual baryons.

gr-qc↗

arXiv2022

Horndeski Proca stars with vector hair

We study Proca stars in a vector-tensor gravity model inspired by Horndeski's generalized Einstein-Maxwell field equations, supplemented with a mass term for the vector field. We discuss the effects of the non-minimal coupling term on the properties of the resulting Proca stars. %and show that they can form vector hair. We show that the sign of the coupling constant is crucial in determining the generic properties of these generalized Proca star solutions, as soon as the magnitude of the coupling constant is sufficiently large to allow for significant deviations from the standard Proca star case. For negative coupling constant we observe a new type of limiting behavior for the generalized Proca stars, where the spacetime splits into an interior region with matter fields and an exterior Schwarzschild region.

gr-qc↗

arXiv2021

Spherically symmetric charged black holes with wavy scalar hair

We study standard Einstein-Maxwell theory minimally coupled to a complex valued and self-interacting scalar field. We demonstrate that new, previously unnoticed spherically symmetric, charged black hole solutions with scalar hair exist in this model for sufficiently large gravitational coupling and sufficiently small electromagnetic coupling. The novel scalar hair has the form of a spatially oscillating ''wave packet'' and back-reacts on the space-time such that both the Ricci and the Kretschmann scalar, respectively, possess qualitatively similar oscillations.

gr-qc↗

arXiv2021

Scalarized dyonic black holes in vector-tensor Horndeski gravity

The vector-tensor Horndeski theory is supplemented by a real, massless scalar field non-minimally coupled to the Horndeski interaction term. The generic dyonic Reissner-Nordstrom solutions characterized by electric and magnetic charges, acquire an instability and bifurcate into electromagnetically charged solutions presenting an horizon and a cloud of scalar hairs at specific values of the non-minimal coupling constant. These hairy black holes are studied in terms of the physical parameters of the model and the critical phenomena limiting their domain of existence are discussed.

gr-qc↗

arXiv2020

Scalarized compact objects in a vector-tensor Horndeski gravity

We have discovered a new type of scalarized charged black holes in a surprisingly simple system: an Einstein-Maxwell-Klein-Gordon field theory where the three fields couple non-minimally through a Horndeski vector-tensor term. In addition to hairy charged black holes, this system exhibits Horndeski-Reissner-Nordstrom solutions and ordinary Reissner-Nordstrom ones which bifurcate to the scalarized solutions. There exist also vector-tensor black hole solutions which possess central curvature singularities although their metric components are finite there, and also solutions with naked singularities producing regular metric components everywhere around them. We analyze the solutions and present their main features.

gr-qc↗

arXiv2020

Inflation inside non-topological defects and scalar black holes

In this paper, we demonstrate that a phenomenon described as "topological inflation" during which inflation occurs inside the core of topological defects, has a non-topological counterpart. This appears in a simple set-up containing Einstein gravity coupled minimally to an electromagnetic field as well as a self-interacting, complex valued scalar field. The U(1) symmetry of the model is unbroken and leads to the existence of globally regular solutions, so-called boson stars, that develop a horizon for sufficiently strong gravitational coupling. We also find that the same phenomenon exists for black holes with scalar hair.

gr-qc↗

arXiv2020

Gravitating bubbles of gluon plasma above deconfinement temperature

The equation of state of SU(3) Yang-Mills theory can be modelled by an effective $Z_3-$symmetric potential $V(\vertϕ\vert,ϕ^3+ϕ^{3*}, T)$ depending on the temperature $T$ and on a scalar field $ϕ$ -- the averaged Polyakov loop. Allowing $ϕ$ to be dynamical opens the way to the study of spatially localized classical configurations of the Polyakov loop. We first show that spherically symmetric static Q-balls exist in the range $(1-1.21)\times T_c$, $T_c$ being the deconfinement temperature. Then we argue that Q-holes solutions, if any are unphysical within our framework. Finally we couple the Polyakov-loop Lagrangian to Einstein gravity and show that spherically symmetric static boson stars exist in the same range of temperature. The Q-ball and boson star solutions we find can be interpreted as "bubbles" of deconfined gluonic matter; their mean radius is always smaller than 10 fm.

hep-ph↗

arXiv2020

Scalarized-charged wormholes in Einstein-Gauss-Bonnet gravity

The Einstein-Maxwell-Klein-Gordon Lagrangian is supplemented by a non-minimal coupling of the real scalar field to the Gauss-Bonnet invariant. The non minimal coupling function is chosen as a general second degree polynomial in the scalar field for which the system is known to admit hairy black holes. The new interaction leads naturally to a violation of the null energy condition, allowing for wormholes to exist without the need of exotic matter. Spherically symmetric, charged wormholes are constructed and their domain of existence is determined in terms of the different choices of the non-minimal coupling constants and of the electric charge. A special emphasis is set to the case of the purely quadratic coupling function. A phenomenon reminiscent to spontaneously scalarised black holes occurs for wormholes. The interaction with the electromagnetic field leads to new families of wormholes supported by a non-vanishing, large enough, electric charge.

gr-qc↗

arXiv2019

The covariance of chiral fermions theory

The quasiclassical theory of massless chiral fermions is considered. The effective action is derived using time-dependent variational principle which provides a clear interpretation of relevant canonical variables. As a result their transformation properties under the action of Lorentz group are derived from first principles.

hep-th↗

arXiv2018

Wireless Communications and Control for Swarms of Cellular-Connected UAVs

By using wireless connectivity through cellular base stations (BSs), swarms of unmanned aerial vehicles (UAVs) can provide a plethora of services ranging from delivery of goods to surveillance. In particular, UAVs in a swarm can utilize wireless communications to collect information, like velocity and heading angle, from surrounding UAVs for coordinating their operations and maintaining target speed and intra-UAV distance. However, due to the uncertainty of the wireless channel, wireless communications among UAVs will experience a transmission delay which can impair the swarm's ability to stabilize system operation. In this paper, the problem of joint communication and control is studied for a swarm of three cellular-connected UAVs positioned in a triangle formation. In particular, a novel approach is proposed for optimizing the swarm's operation while jointly considering the delay of the wireless network and the stability of the control system. Based on this approach, the maximum allowable delay required to prevent the instability of the swarm is determined. Moreover, by using stochastic geometry, the reliability of the wireless network is derived as the probability of meeting the stability requirement of the control system. The simulation results validate the effectiveness of the proposed joint strategy, and help obtain insightful design guidelines on how to form a stable swarm of UAVs.

eess.SP↗

arXiv2018

Nutty black holes in galileon scalar-tensor gravity

Einstein gravity supplemented by a scalar field non-minimally coupled to a Gauss-Bonnet term provides an example of model of scalar-tensor gravity where hairy black holes do exist. We consider the classical equations within a metric endowed with a NUT-charge and obtain a two-parameter family of nutty-hairy black holes. The pattern of these solutions in the exterior and the interior of their horizon is studied in some details. The influence of both -- the hairs and the NUT-charge -- on the lightlike and timelike geodesics is emphasized.

gr-qc↗

arXiv2018

Spinning-Charged-Hairy Black Holes in 5-d Einstein gravity

The spinning-hairy black holes that occur in Einstein gravity supplemented by a doublet of complex scalar fields are constructed within an extension of the model by a $U(1)$ gauge symmetry involving a massless vector potential. The hairy black holes then acquire an electric charge and a magnetic moment; their domain of existence is discussed in terms of the gauge coupling constant.

gr-qc↗

arXiv2018

Charged Boson Stars and Black Holes with Non-Minimal Coupling to Gravity

We find new spherically symmetric charged boson star solutions of a complex scalar field coupled non-minimally to gravity by a "John-type" term of Horndeski theory, that is a coupling between the kinetic scalar term and Einstein tensor. We study the parameter space of the solutions and find two distinct families according to their position in parameter space. More widespread is the family of solutions (which we call branch 1) existing for a finite interval of the central value of the scalar field starting from zero and ending at some finite maximal value. This branch contains as a special case the charged boson stars of the minimally coupled theory. In some regions of parameter space we find a new second branch ("branch 2") of solutions which are more massive and more stable than those of branch 1. This second branch exists also in a finite interval of the central value of the scalar field, but its end points (either both or in some cases only one) are extremal Reissner-Nordstrom black hole solutions.

gr-qc↗

arXiv2017

Proca Q Balls and their Coupling to Gravity

Extending the Proca Lagrangian of a massive complex-valued vector field by self-interaction potential, we construct a large class of spherically symmetric solutions in flat Minkowski background as well as in the self-gravitating case. Our solutions encompass Proca Q-balls and Proca stars known in the literature, but present new features and go beyond the limited region of parameter space charted so far. A special emphasis is set to the domain of existence of the solutions in relation with the coupling constants of the potential and to the critical phenomena limiting this domain.

gr-qc↗

arXiv2017

Proca Q Tubes and their Coupling to Gravity

The Einstein-Proca system is studied in the case of a complex vector-field self-interacting through an appropriate potential with a global U(1) symmetry. The corresponding equations for a static, cylindrically symmetric metric and matter fields are then constructed and solved. In the probe limit (no gravity), it is shown that the equations admit at least two classes of regular solutions distinguished by the asymptotic behavior of the matter fields. One of these classes corresponds to lumps of vector fields localized in a cylindrical region, we naturally call these solutions "Proca-Q-tubes". They constitute the cylindrical counterparts of spherical Proca-Q-balls constructed recently, they can be characterized by finite mass and charge per unit-length of the tube. The domain of existence of these Proca-Q-tubes with respect to the coupling constants determining the potential is studied in detail. Finally, the gravitating Proca-Q-tubes are constructed and studied.

gr-qc↗