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D. H. Tchrakian

Publications and source records attributed to D. H. Tchrakian.

At least 73 records · Page 4Linked to original sources
arXiv2006

Features of gravity-Yang-Mills hierarchies in d-dimensions

Higher dimensional, direct analogues of the usual d=4 Einstein--Yang-Mills (EYM) systems are studied. These consist of the gravitational and Yang-Mills hierarchies in d=4p dimensional spacetimes, both consisting of 2p-form curvature terms only. Regular and black hole solutions are constructed in $2p+2\le d \le 4p$, in which dimensions the total mass-energy is finite, generalising the familiar Bartnik-McKinnon solutions in EYM theory for p=1. In d=4p, this similarity is complete. In the special case of d=2p+1, just beyond the finite energy range of d, exact solutions in closed form are found. Finally, d=2p+1 purely gravitational systems, whose solutions generalise the static d=3 BTZ solutions, are discussed.

gr-qc↗
arXiv2005

No hair conjecture, nonabelian hierarchies and anti-de Sitter spacetime

We consider globally regular and black holes solutions for the Einstein-Yang-Mills system with negative cosmological constant in $d-$spacetime dimensions. We find that the ADM mass of the spherically symmetric solutions generically diverges for $d>4$. Solutions with finite mass are found by considering corrections to the YM Lagrangean consisting in higher therm of the Yang--Mills hierarchy. Such systems can occur in the low energy effective action of string theory. A discussion of the main properties of the solutions and the differences with respect to the four dimensional case is presented. The mass of these configurations is computed by using a counterterm method.

gr-qc↗
arXiv2005

Spinning U(1) gauged Skyrmions

We construct axially symmetric solutions of U(1) gauged Skyrme model. Possessing a nonvanishing magnetic moment, these solitons have also a nonzero angular momentum proportional to the electric charge.

hep-th↗
arXiv2005

Regular solutions to higher order curvature Einstein--Yang-Mills systems in higher dimensions

We study regular, static, spherically symmetric solutions of Yang-Mills theories employing higher order invariants of the field strength coupled to gravity in $d$ dimensions. We consider models with only two such invariants characterised by integers $p$ and $q$. These models depend on one dimensionless parameter $α$ leading to one-parameter families of regular solutions, obtainable by numerical solution of the corresponding boundary value problem. Much emphasis is put on an analytical understanding of the numerical results.

gr-qc↗
arXiv2005

Yang--Mills sphalerons in all even spacetime dimensions $d=2k$, $k>2$ : $k$=3,4

The classical solutions to higher dimensional Yang--Mills (YM) systems, which are integral parts of higher dimensional Einstein--YM (EYM) systems, are studied. These are the gravity decoupling limits of the fully gravitating EYM solutions. In odd spacetime dimensions, depending on the choice of gauge group, these are either topologically stable or unstable. Both cases are analysed, the latter numerically only. In even spacetime dimensions they are always unstable, describing saddle points of the energy, and can be described as {\it sphalerons}. This instability is analysed by constructing the noncontractible loops and calculating the Chern--Simons (CS) charges, and also perturbatively by numerically constructing the negative modes. This study is restricted to the simplest YM system in spacetime dimensions $d=6,7,8$, which is amply illustrative of the generic case.

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

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

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

Localisation of Fermions to brane: Codimension $d \geq 2$

We investigate $4+d$ dimensional fermionic models in which the system in codimension-$d$ supports a topologically stable solution, and in which the fermion may be localised to the brane, with power law in 'instanton' backgrounds and exponentially in 'soliton' backgrounds. When the fermions are isoscalars, the mechanism fails, while for isospinor fermions it is successful. As backgrounds we consider instantons of Yang--Mills and sigma models in even codimensions, solitons of sigma models in odd codimensions, as well as solitons of Higgs and Goldstone models in all codimensions.

hep-th↗
arXiv2003

Higher order curvature generalisations of Bartnick-McKinnon and coloured black hole solutions in $d=5$

We construct globally regular as well as non-abelian black hole solutions of a higher order curvature Einstein-Yang-Mills (EYM) model in $d=5$ dimensions. This model consists of the superposition of the first two members of the gravitational hierarchy (Einstein plus first Gauss-Bonnet(GB)) interacting with the superposition of the first two members of the $SO(d)$ Yang--Mills hierarchy.

hep-th↗
arXiv2002

An extended model for monopole catalysis of nucleon decay

A new model for monopole catalysis of nucleon decay is proposed. Unlike in the earlier one, the only light fields in this model are the photon and Skyrme (pion) field. The model admits the 't Hooft- Polyakov monopole and Skyrmion as classical solutions, while baryon number non-conservation occurs through an anomaly involving an intermediate mass axial vector field resembling W- and Z-bosons. By considering spherically symmetric monopole-Skyrmion configurations, we find that the Skyrmion looses essentially all its mass when interacting with the monopole, which is phenomenologically identical to the monopole catalysis of nucleon decay. Short-distance monopole-Skyrmion physics in this model is interesting too, as there exist almost degenerate metastable monopole-Skyrmion bound states separated by substantial energy barriers. Yet the heights of the latter are much smaller than the physical nucleon mass, so the complete disappearance of the normal undeformed Skyrmion remains perfectly possible in Skyrmion-monopole scattering.

hep-th↗
arXiv2002

Skyrmed Monopoles

We investigate multi-monopole solutions of a modified version of the BPS Yang-Mills-Higgs model in which a term quartic in the covariant derivatives of the Higgs field (a Skyrme term) is included in the Lagrangian. Using numerical methods we find that this modification leads to multi-monopole bound states. We compute axially symmetric monopoles up to charge five and also monopoles with Platonic symmetry for charges three, four and five. The numerical evidence suggests that, in contrast to Skyrmions, the minimal energy Skyrmed monopoles are axially symmetric.

hep-th↗
arXiv2002

Non-factorisable metrics and Gauss--Bonnet terms in higher dimensions

An iterative construction of higher order Einstein tensors for a maximally Gauss-Bonnet extended gravitational Lagrangian was introduced in a previous paper. Here the formalism is extended to non-factorisable metrics in arbitrary ($d+1$) dimensions in the presence of superposed Gauss-Bonnet terms. Such a generalisation turns out to be remarkably convenient and elegant. Having thus obtained the variational equations we first construct bulk solutions, with nonzero and zero cosmological constant. It is also pointed out that in the absence of Gauss-Bonnet terms a Schwarzschild type solution can be obtained in the non-factorisable case. Two positive tension branes are then inserted and their tensions are obtained in terms of parameters in the warp factor. Relations to recent studies of several authors are pointed out.

hep-th↗
arXiv2002

Particle-like solutions to higher order curvature Einstein--Yang-Mills systems in d dimensions

We consider the superposition of the first two members of the gravitational hierarchy (Einstein plus first Gauss-Bonnet(GB)) interacting with the superposition of the first two members of the $SO_{(\pm)}(d)$ Yang--Mills hierarchy, in $d$ dimensions. Such systems can occur in the low energy effective action of string theory. Particle-like solutions %for the systems with only an Einstein term, and with only a GB term, in dimensions $d=6,8$ are constructed respectively. Our results reveal qualitatively new properties featuring double-valued solutions with critical behaviour. In this preliminary study, we have restricted ourselves to one-node solutions.

hep-th↗
arXiv2002

The 1-soliton in the SO(3) gauged Skyrme model with mass term

The solitons of the SO(3) gauged Skyrme model with no pion-mass potential were studied in Refs. {nl,jmp}. Here, the effects of the inclusion of this potential are studied. In contrast with the (ungauged) Skyrme model, where the effect of this potential on the solitons is marginal, here it turns out to be decisive, resulting in very different dependence of the energy as a function of the Skyrme coupling constant.

hep-th↗