arXiv subjects

Eugen Radu

Publications and source records attributed to Eugen Radu.

At least 253 records · Page 14Linked to original sources

arXiv2005

On cosmological solutions in a spontaneously broken gauge theory

We consider solutions of the Yang-Mills-Higgs system coupled to gravity in asymptotically de Sitter spacetime. The basic features of two classes of solutions are discussed, one of them corresponding to magnetic monopoles, the other one to sphalerons. We find that although the total mass within the cosmological horizon of these configurations is finite, their mass evaluated at timelike infinity generically diverges. Also, no solutions exist in the absence of a Higgs potential.

hep-th↗

arXiv2005

On a Petrov-type D homogeneous solution

We present a new two-parameter family of solutions of Einstein gravity with negative cosmological constant in 2+1 dimensions. These solutions are obtained by squashing the anti-de Sitter geometry along one direction and posses four Killing vectors. Global properties as well as the four dimensional generalization are discussed, followed by the investigation of the geodesic motion. A simple global embedding of these spaces as the intersection of four quadratic surfaces in a seven dimensional space is obtained. We argue also that these geometries describe the boundary of a four dimensional nutty-bubble solution and are relevant in the context of AdS/CFT correspondence.

gr-qc↗

arXiv2005

Conformally coupled scalar solitons and black holes with negative cosmological constant

We present arguments for the existence of both globally regular and black hole solutions of the Einstein equations with a conformally coupled scalar field, in the presence of a negative cosmological constant, for space-time dimensions greater than or equal to four. These configurations approach asymptotically anti-de Sitter spacetime and are indexed by the central value of the scalar field. We also study the stability of these solutions, and show that, at least for all the solutions studied numerically, they are linearly stable.

gr-qc↗

arXiv2005

Nutty dyons

We argue that the Einstein-Yang-Mills-Higgs theory presents nontrivial solutions with a NUT charge. These solutions approach asymptotically the Taub-NUT spacetime and generalize the known dyon black hole configurations. The main properties of the solutions and the differences with respect to the asymptotically flat case are discussed. We find that a nonabelian magnetic monopole placed in the field of gravitational dyon necessarily acquires an electric field, while the magnetic charge may take arbitrary values.

gr-qc↗

arXiv2005

Deformed vortices in (4+1)-dimensional Einstein-Yang-Mills theory

We study vortex-type solutions in a (4+1)-dimensional Einstein-Yang-Mills-SU(2) model. Assuming all fields to be independent on the extra coordinate, these solutions correspond in a four dimensional picture to axially symmetric multimonopoles, respectively monopole-antimonopole solutions. By boosting the five dimensional purely magnetic solutions we find new configurations which in four dimensions represents rotating regular nonabelian solutions with an additional electric charge.

hep-th↗

arXiv2005

New axially symmetric Yang-Mills-Higgs solutions with negative cosmological constant

We construct numerically new axially symmetric solutions of SU(2) Yang-Mills-Higgs theory in $(3+1)$ anti-de Sitter spacetime. Two types of finite energy, regular configurations are considered: multimonopole solutions with magnetic charge $n>1$ and monopole-antimonopole pairs with zero net magnetic charge. A somewhat detailed analysis of the boundary conditions for axially symmetric solutions is presented. The properties of these solutions are investigated, with a view to compare with those on a flat spacetime background. The basic properties of the gravitating generalizations of these configurations are also discussed.

hep-th↗

arXiv2005

Breakdown of the Entropy/Area Relationship for NUT-charged Spacetimes

We demonstrate that $(D+1)$-dimensional, locally asymptotically anti-deSitter spacetimes with nonzero NUT charge generically do not respect the usual relationship between area and entropy. This result does not depend on either the existence of closed timelike curves nor on the removal of Misner string singularities, but instead is a consequence of the first law of thermodynamics.

hep-th↗

arXiv2005

Static BPS 'monopoles' in all even spacetime dimensions

Two families of SO(2n) Higgs models in $2n$ dimensional spacetime are presented. One family arises from the {\it dimensional reduction} of higher dimensional Yang-Mills systems while the construction of the other one is {\it ad hoc}, the $n=2$ member of each family coinciding with the usual SU(2) Yang-Mills--Higgs system without Higgs potential. All models support BPS 'monopole' solutions. The 'dyons' of the {\it dimensionally descended} models are also BPS, while the electrically charged solutions of the {\it ad hoc} models are not BPS.

hep-th↗

arXiv2005

New hairy black hole solutions with a dilaton potential

We consider black hole solutions with a dilaton field possessing a nontrivial potential approaching a constant negative value at infinity. The asymptotic behaviour of the dilaton field is assumed to be slower than that of a localized distribution of matter. A nonabelian SU(2) gauge field is also included in the total action. The mass of the solutions admitting a power series expansion in $1/r$ at infinity and preserving the asymptotic anti-de Sitter geometry is computed by using a counterterm subtraction method. Numerical arguments are presented for the existence of hairy black hole solutions for a dilaton potential of the form $V(ϕ)=C_1 \exp(2α_1 ϕ)+C_2 \exp(2α_2 ϕ)+C_3$, special attention being paid to the case of ${\cal N}=4, D=4$ gauged supergravity model of Gates and Zwiebach.

hep-th↗

arXiv2005

Rotating regular solutions in Einstein-Yang-Mills-Higgs theory

We construct new axially symmetric rotating solutions of Einstein-Yang-Mills-Higgs theory. These globally regular configurations possess a nonvanishing electric charge which equals the total angular momentum, and zero topological charge, representing a monopole-antimonopole system rotating around the symmetry axis through their common center of mass.

hep-th↗

arXiv2004

Boson stars in SU(2) Yang-Mills-scalar field theories

We present new spherically symmetric solutions of an SU(2) Einstein-Yang-Mills model coupled to a doublet of scalar fields. Sequences of asymptotically flat, Yang-Mills-boson star-type configurations are constructed numerically by considering an appropriate time-dependent ansatz for the complex scalar field and a static, purely magnetic SU(2)-Yang-Mills potential. Both nodeless as well as solutions with nodes of the scalar field and gauge potential are considered. We find that these solutions share many features with the "pure'' boson stars.

hep-th↗

arXiv2004

Nut Charged Space-times and Closed Timelike Curves on the Boundary

We consider higher dimensional generalizations of the four dimensional topological Taub-NUT-AdS solutions, where the angular spheres are replaced by planes and hyperboloids. The thermodynamics of these configurations is discussed to some extent. The results we find suggest that the entropy/area relation is always violated in the presence of a NUT charge. We argue also that the conjectured AdS/CFT correspondence may teach us something about the physics in spacetimes containing closed timelike curves. To this aim, we use the observation that the boundary metric of a (D+1)-dimensional Taub-NUT-AdS solution provides a D-dimensional generalization of the known Gödel-type spacetimes.

hep-th↗

arXiv2004

Gravitating Yang-Mills dyon vortices in 4+1 spacetime dimensions

We consider vortex-type solutions in $d=5$ dimensions of the Einstein gravity coupled to a nonabelian SU(2) field posessing a nonzero electric part. After the dimensional reduction, this corresponds to a $d=4$ Einstein-Yang-Mills-Higgs-U(1)-dilaton model. A general axially symmetric ansatz is presented, and the properties of the spherically symmetric solutions are analysed.

hep-th↗

arXiv2004

Static axially symmetric solutions of Einstein-Yang-Mills equations with a negative cosmological constant: black hole solutions

We investigate static axially symmetric black hole solutions in a four-dimensional Einstein-Yang-Mills-SU(2) theory with a negative cosmological constant $Λ$. These solutions approach asymptotically the anti-de Sitter spacetime and possess a regular event horizon. A discussion of the main properties of the solutions and the differences with respect to the asymptotically flat case is presented. The mass of these configurations is computed by using a counterterm method. We note that the $Λ=-3$ configurations have an higher dimensional interpretation in context of $d=11$ supergravity. The existence of axially symmetric monopole and dyon solutions in a fixed Schwarzschild-anti-de Sitter background is also discussed. An exact solution of the Einstein-Yang-Mills equations is presented in Appendix.

hep-th↗

arXiv2004

Regular and black hole solutions to higher order curvature Einstein--Yang-Mills--Grassmannian systems in 5 dimensions

We construct both regular and black hole spherically symmetric solutions to the original higher curvature EYM model augmented by a Grassmannian sigma model field in $d=5$ spacetime dimensions. Unlike the original model, the new model supports regular solutions in the flat space limit. We find that a peculiar singular behaviour of the solutions in the original model, persists in the case of the modified model too. A study of the solutions to the Grassmannian model in flat space is also carried out.

hep-th↗

arXiv2004

Melvin solution with a dilaton potential

We find new Melvin-like solutions in Einstein-Maxwell-dilaton gravity with a Liouville-type dilaton potential. The properties of the corresponding solution in Freedman-Schwarz gauged supergravity model are extensively studied. We show that this configuration is regular and geodesically complete but do not preserve any supersymmetry. An exact solution describing travelling waves in this Melvin-type background is also presented.

gr-qc↗

arXiv2004

Rotating Boson Stars in 2+1 Dimensions

We consider rotating boson star solutions in a three-dimensional anti-de Sitter spacetime and investigate the influence of the rotation on their properties. The mass and angular momentum of these configurations are computed by using the counterterm method. No regular solution is found in the limit of vanishing cosmological constant.

gr-qc↗

arXiv2003

Reissner-Nordstrom-de Sitter black hole, planar coordinates and dS/CFT

We discuss the Reissner-Nordstrom-de Sitter black holes in the context of dS/CFT correspondence by using static and planar coordinates. The boundary stress tensor and the mass of the solutions are computed. Also, we investigate how the RG flow is changed for different foliations. The Kastor-Traschen multi-black hole solution is considered as well as AdS counterparts of these configurations. In particular, we find that in planar coordinates the black holes appear like punctures in the dual boundary theory.

hep-th↗