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Eugen Radu

Publications and source records attributed to Eugen Radu.

At least 217 records · Page 12Linked to original sources
arXiv2009

Gravitating Yang--Mills fields in all dimensions

A classification of gravitating Yang--Mills systems in all dimensions is presented. These systems are set up so that they support finite energy solutions. Both regular and black hole solutions are considered, the former being the limit of the latter for vanishing event horizon radius. Special attention is paid to systems necessarily involving higher order Yang--Mills curvature terms, along with the option of incorporating higher order terms in the Riemann curvature. The scope here is restricted to Einstein systems, with or without cosmological constant, and the Yang--Mills(--Higgs) systems.

gr-qc↗
arXiv2009

Spinning Electroweak Sphalerons

We present numerical evidence for the existence of stationary spinning generalizations for the static sphaleron in the Weinberg-Salam theory. Our results suggest that, for any value of the mixing angle $\thetw$ and for any Higgs mass, the spinning sphalerons comprise a family labeled by their angular momentum $J$. For $\thetw\neq 0$ they possess an electric charge $Q=eJ$ where $e$ is the electron charge. Inside they contain a monopole-antimonopole pair and a spinning loop of electric current, and for large $J$ they show a Regge-type behavior. It is likely that these sphalerons mediate the topological transitions in sectors with $J\neq 0$, thus enlarging the number of transition channels. Their action {\it decreases} with $J$, which may considerably affect the total transition rate.

hep-th↗
arXiv2009

Harrison transformation and charged black objects in Kaluza-Klein theory

We generate charged black brane solutions in $D-$dimensions in a theory of gravity coupled to a dilaton and an antisymmetric form, by using a Harrison-type transformation. The seed vacuum solutions that we use correspond to uplifted Kaluza-Klein black strings and black holes in $(D-p)$-dimensions. A generalization of the Marolf-Mann quasilocal formalism to the Kaluza-Klein theory is also presented, the global charges of the black objects being computed in this way. We argue that the thermodynamics of the charged solutions can be derived from that of the vacuum configurations. Our results show that all charged Kaluza-Klein solutions constructed by means of Harrison transformations are thermodynamically unstable in a grand canonical ensemble. The general formalism is applied to the case of nonuniform black strings and caged black hole solutions in $D=5, 6$ Einstein-Maxwell-dilaton gravity, whose geometrical properties and thermodynamics are discussed. We argue that the topology changing transition scenario, which was previously proposed in the vacuum case, also holds in this case. Spinning generalizations of the charged black strings are constructed in six dimensions in the slowly rotating limit. We find that the gyromagnetic ratio of these solutions possesses a nontrivial dependence on the nonuniformity parameter.

hep-th↗
arXiv2009

$d\geq 5$ static black holes with $S^2\times S^{d-4}$ event horizon topology

We present numerical evidence for the existence of new black hole solutions in $d\geq 6$ spacetime dimensions. They approach asymptotically the Minkowski background and have an event horizon topology $S^2\times S^{d-4}$. These static solutions share the basic properties of the nonrotating black rings in five dimensions, in particular the presence of a conical singularity.

hep-th↗
arXiv2009

From black strings to black holes: nuttier and squashed AdS$_5$ solutions

We construct new solutions of the Einstein equations with negative cosmological constant in five spacetime dimensions. They smoothly emerge as deformations of the known AdS$_5$ black strings. The first type of configurations can be viewed as the $d=4$ Taub-NUT-AdS solutions uplifted to five dimensions, in the presence of a negative cosmological constant. We argue that these solutions provide the gravity dual for a ${\cal N}=4$ super-Yang-Mills theory formulated in a $d=4$ homogeneous Gödel-type spacetime background. A different deformation of the AdS$_5$ black strings leads to squashed AdS black holes and their topological generalizations. In this case, the conformal infinity is the product of time and a circle-fibration over a base space that is a two-dimensional Einstein space.

gr-qc↗
arXiv2008

New AdS non Abelian black holes with superconducting horizons

We present arguments for the existence of higher dimensional asymptotically AdS non Abelian black holes with a Ricci flat event horizon and analyze their basic properties. Unlike higher dimensional black holes with a curved horizon, of the usual Einstein-Yang-Mills system, these solutions have finite mass-energy. Below some non-zero critical temperature, they are thermodynamically preferred over the Abelian configurations.

hep-th↗
arXiv2008

Non Abelian Chern-Simons-Higgs solutions in (2+1) dimensions

Non Abelian vortices of a SU(2) Chern-Simons--Higgs theory in 2+1 dimensions are constructed numerically. They represent natural counterparts of the U(1) solutions considered by Hong, Kim and Pac, and, by Jackiw and Weinberg. The Abelian embeddings are identified, for all values of the Higgs selfinteraction strength $ν$, resulting in both attractive and repulsive phases. A detailed analysis of the properties of the solutions reveals the existence ofa number of unexpected features. For a certain range of the parameter $ν$, it is shown that the non Abelian vortices have lower energy than their topologically stable Abelian counterparts, resulting in an effective energy lower bound on the SU(2) configurations. The angular momentum of these vortices is analysed and it is found that unlike the Abelian ones, whose angular momentum and energy are unrelated, there is a nontrivial mass--spin relation of the non Abelian vortices.

hep-th↗
arXiv2008

Charging Black Saturn?

We construct new charged static solutions of the Einstein-Maxwell field equations in five dimensions via a solution generation technique utilizing the symmetries of the reduced Lagrangian. By applying our method on the multi-Reissner-Nordstrom solution in four dimensions, we generate the multi-Reissner-Nordstrom solution in five dimensions. We focus on the five-dimensional solution describing a pair of charged black objects with general masses and electric charges. This solution includes the double Reissner-Nordstrom solution as well as the charged version of the five-dimensional static black Saturn. However, all the black Saturn configurations that we could find present either a conical singularity or a naked singularity. We also obtain a non-extremal configuration of charged black strings that reduces in the extremal limit to a Majumdar-Papapetrou like solution in five dimensions.

hep-th↗
arXiv2008

Black objects in the Einstein-Gauss-Bonnet theory with negative cosmological constant and the boundary counterterm method

We propose to compute the action and global charges of the asymptotically anti-de Sitter solutions in Einstein-Gauss-Bonnet theory by adding boundary counterterms to the gravitational action. The general expression of the counterterms and the boundary stress tensor is presented for spacetimes of dimension $d\leq 9$. We apply this tehnique for several different types of black objects. Apart from static and rotating black holes, we consider also Einstein-Gauss-Bonnet black string solutions with negative cosmological constant.

gr-qc↗
arXiv2008

Stationary ring solitons in field theory - knots and vortons

We review the current status of the problem of constructing classical field theory solutions describing stationary vortex rings in Minkowski space in 3+1 dimensions. We describe the known up to date solutions of this type, such as the static knot solitons stabilized by the topological Hopf charge, the attempts to gauge them, the anomalous solitons stabilized by the Chern-Simons number, as well as the non-Abelian monopole and sphaleron rings. Passing to the rotating solutions, we first discuss the conditions insuring that they do not radiate, and then describe the spinning $Q$-balls, their twisted and gauged generalizations reported here for the first time, spinning skyrmions, and rotating monopole-antimonopole pairs. We then present the first explicit construction of global vortons as solutions of the elliptic boundary value problem, which demonstrates their non-radiating character. Finally, we describe the analogs of vortons in the Bose-Einstein condensates, analogs of spinning $Q$-balls in the non-linear optics, and also moving vortex rings in superfluid helium and in ferromagnetics.

hep-th↗
arXiv2007

d=4+1 gravitating nonabelian solutions with bi-azimuthal symmetry

We construct static, asymptotically flat solutions of SU(2) Einstein-Yang-Mills theory in 4+1 dimensions, subject to bi-azimuthal symmetry. Both particle-like and black hole solutions are considered for two different sets of boundary conditions in the Yang--Mills sector, corresponding to multisolitons and soliton-antisoliton pairs. For gravitating multi-soliton solutions, we find that their mass per unit charge is lower than the mass of the corresponding unit charge, spherically symmetric soliton.

hep-th↗
arXiv2007

Nonabelian solutions in a Melvin magnetic universe

We show the existence of D=4 nonabelian solutions approaching asymptotically a dilatonic Melvin spacetime background. An exact solution generalizing the Chamseddine-Volkov soliton for a nonzero external U(1) magnetic field is also reported.

hep-th↗
arXiv2007

Black strings with negative cosmological constant: inclusion of electric charge and rotation

We generalize the vacuum static black strings with negative cosmological constant recently discussed in literature, by including an electromagnetic field. These higher-dimensional configurations have no dependence on the `compact' extra dimension, and their boundary topology is the product of time and $S^{d-3}\times S^1$ or $H^{d-3}\times S^1$. Rotating generalizations of the even dimensional black string configurations are considered as well. Different from the static, neutral case, no regular limit is found for a vanishing event horizon radius. We explore numerically the general properties of such solutions and, using a counterterm prescription, we compute their conserved charges and discuss their thermodynamics. We find that the thermodynamics of the black strings follows the pattern of the corresponding black hole solutions in AdS backgrounds.

hep-th↗
arXiv2007

Spherically symmetric selfdual Yang-Mills instantons on curved backgrounds in all even dimensions

We present several different classes of selfdual Yang-Mills instantons in all even d backgrounds with Euclidean signature. In d=4p+2 the only solutions we found are on constant curvature dS and AdS backgrounds, and are evaluated in closed form. In d=4p an interesting class of instantons are given on black hole backgrounds. One class of solutions are (Euclidean) time-independent and spherically symmetric in d-1 dimensions, and the other class are spherically symmetric in all d dimensions. Some of the solutions in the former class are evaluated numerically, all the rest being given in closed form. Analytic proofs of existence covering all numerically evaluated solutions are given. All instantons studied have finite action and vanishing energy momentum tensor and do not disturb the geometry.

hep-th↗
arXiv2007

Goldstone models in D+1 dimensions, D=3,4,5, supporting stable and zero topological charge solutions

We study finite energy static solutions to a global symmetry breaking Goldstone model described by an isovector scalar field in D+1 spacetime dimensions. Both topologically stable multisolitons with arbitrary winding numbers, and zero topological charge soliton--antisoliton solutions are constructed numerically in D=3,4,5. We have explored the types of symmetries the systems should be subjected to, for there to exist multisoliton and soliton--antisoliton pairs in D=3,4,5,6. These findings are underpinned by constructing numerical solutions in the $D\le 5$ examples. Subject to axial symmetry, only multisolitons of all topological charges exist in even D, and in odd D, only zero and unit topological charge solutions exist. Subjecting the system to weaker than axial symmetries, results in the existence of all the possibilities in all dimensions. Our findings apply also to finite 'energy' solutions to Yang--Mills and Yang-Mills--Higgs systems, and in principle also sigma models.

hep-th↗
arXiv2007

Rotating nonuniform black string solutions

We explore via linearized perturbation theory the Gregory-Laflamme instability of rotating black strings with equal magnitude angular momenta. Our results indicate that the Gregory-Laflamme instability persists up to extremality for all even dimensions between six and fourteen. We construct rotating nonuniform black strings with two equal magnitude angular momenta in six dimensions. We see a first indication for the occurrence of a topology changing transition, associated with such rotating nonuniform black strings. Charged nonuniform black string configurations in heterotic string theory are also constructed by employing a solution generation technique.

hep-th↗
arXiv2007

Particle-like solutions to the Yang--Mills-dilaton system in d=4+1 dimensions

We construct static solutions to a SU(2) Yang--Mills (YM) dilaton model in 4+1 dimensions subject to bi-azimuthal symmetry. The YM sector of the model consists of the usual YM term and the next higher order term of the YM hierarchy, which is required by the scaling condition for the existence of finite energy solutions. The basic features of two different types of configurations are studied, corresponding to (multi)solitons with topological charge $n^2$, and soliton--antisoliton pairs with zero topological charge.

hep-th↗