arXiv subjects

Yasha Shnir

Publications and source records attributed to Yasha Shnir.

At least 19 recordsLinked to original sources

arXiv2015

Static black holes with axial symmetry in asymptotically AdS$_4$ spacetime

The known static electro-vacuum black holes in a globally AdS$_4$ background have an event horizon which is geometrically a round sphere. In this work we argue that the situation is different in models with matter fields possessing an explicit dependence on the azimuthal angle $\varphi$, which, however, does not manifest at the level of the energy-momentum tensor. As a result, the full solutions are axially symmetric only, possessing a single (timelike) Killing vector field. Explicit examples of such static black holes are constructed in Einstein--(complex) scalar field and Einstein--Yang-Mills theories. The basic properties of these solutions are discussed, looking for generic features. For example, we notice that the horizon has an oblate spheroidal shape for solutions with a scalar field and a prolate one for black holes with Yang-Mills fields. The deviation from sphericity of the horizon geometry manifests itself in the holographic stress-tensor. Finally, based on the results obtained in the probe limit, we conjecture the existence in the Einstein-Maxwell theory of static black holes with axial symmetry only.

gr-qc↗

arXiv2015

Boundary scattering in the phi^4 model

We study boundary scattering in the $\phi^4$ model on a half-line with a one-parameter family of Neumann-type boundary conditions. A rich variety of phenomena is observed, which extends previously-studied behaviour on the full line to include regimes of near-elastic scattering, the restoration of a missing scattering window, and the creation of a kink or oscillon through the collision-induced decay of a metastable boundary state. We also study the decay of the vibrational boundary mode, and explore different scenarios for its relaxation and for the creation of kinks.

hep-th↗

arXiv2015

Thermodynamic properties of asymptotically anti-de Sitter black holes in d=4 Einstein-Yang-Mills theory

We investigate the thermodynamics of spherically symmetric black hole solutions in a four-dimensional Einstein--Yang-Mills-SU(2) theory with a negative cosmological constant. Special attention is paid to configurations with a unit magnetic charge. We find that a set of Reissner-Nordstr\"om--Anti-de Sitter black holes can become unstable to forming non-Abelian hair. However, the hairy black holes are never thermodynamically favoured over the full set of abelian monopole solutions. The thermodynamics of the generic configurations possessing a noninteger magnetic charge is also discussed.

hep-th↗

arXiv2014

Non-Abelian fields in AdS$_4$ spacetime: axially symmetric, composite configurations

We construct new finite energy regular solutions in Einstein-Yang-Mills-SU(2) theory. They are static, axially symmetric and approach at infinity the anti-de Sitter spacetime background. These configurations are characterized by a pair of integers $(m, n)$, where $m$ is related to the polar angle and $n$ to the azimuthal angle, being related to the known flat space monopole-antimonopole chains and vortex rings. Generically, they describe composite configurations with several individual components, possesing a nonzero magnetic charge, even in the absence of a Higgs field. Such Yang-Mills configurations exist already in the probe limit, the AdS geometry supplying the attractive force needed to balance the repulsive force of Yang-Mills gauge interactions. The gravitating solutions are constructed by numerically solving the elliptic Einstein-DeTurck--Yang-Mills equations. The variation of the gravitational coupling constant $\alpha$ reveals the existence of two branches of gravitating solutions which bifurcate at some critical value of $\alpha$. The lower energy branch connects to the solutions in the global AdS spacetime, while the upper branch is linked to the generalized Bartnik-McKinnon solutions in asymptotically flat spacetime. Also, a spherically symmetric, closed form solution is found as a perturbation around the globally anti-de Sitter vacuum state.

gr-qc↗

arXiv2012

Axially symmetric Yang-Mills-Higgs solutions in AdS spacetime

We consider axially symmetric solutions of SU(2) Yang-Mills-Higgs theory in globally AdS spacetime and a fixed Schwarzschild-AdS black hole background. The solutions are characterized by two integers $(m,n)$ where $m$ is related to the polar angle and $n$ to the azimuthal angle. Two types of finite energy, regular configurations are considered: solutions with net magnetic charge $n>1$ and monopole-antimonopole pairs and chains with zero net magnetic charge. The configurations are endowed with an electric charge and carry also a nonvanishing angular momentum density.

hep-th↗

arXiv2011

Kink-antikink collisions in the phi^6 model

We study kink-antikink collisions in the one-dimensional non-integrable scalar phi^6 model. Although the single-kink solutions for this model do not possess an internal vibrational mode, our simulations reveal a resonant scattering structure, thereby providing a counterexample to the standard belief that existence of such a mode is a necessary condition for multi-bounce resonances in general kink-antikink collisions. We investigate the two-bounce windows in detail, and present evidence that this structure is caused by existence of bound states in the spectrum of small oscillations about a combined kink-antikink configuration.

hep-th↗

arXiv2007

Gravitating Monopole-Antimonopole Systems at Large Scalar Coupling

We discuss static axially symmetric solutions of SU(2) Einstein-Yang-Mills-Higgs theory for large scalar coupling. These regular asymptotically flat solutions represent monopole-antimonopole chain and vortex ring solutions, as well as new configurations, present only for larger values of the scalar coupling. When gravity is coupled to the Yang-Mills-Higgs system, branches of gravitating solutions emerge from the flat-space solutions, and extend up to critical values of the gravitational coupling constant. For small scalar coupling only two branches of gravitating solutions exist, where the second branch connects to a generalized Bartnik-McKinnon solution. For large scalar coupling, however, a plethora of gravitating branches can be present and indicate the emergence of new flat-space branches.

hep-th↗

arXiv2006

Transitions between Vortex Rings and Monopole-Antimonopole Chains

In monopole-antimonopole chain solutions of SU(2) Yang-Mills-Higgs theory the Higgs field vanishes at m isolated points along the symmetry axis, whereas in vortex ring solutions the Higgs field vanishes along one or more rings, centered around the symmetry axis. We investigate how these static axially symmetric solutions depend on the strength of the Higgs selfcoupling λ. We show, that as the coupling is getting large, new branches of solutions appear at critical values of λ. Exhibiting a different node structure, these give rise to transitions between vortex rings and monopole-antimonopole chains.

hep-th↗

arXiv2005

Monopole-Monopole solutions of Einstein-Yang-Mills-Higgs Theory

New static regular axially symmetric solutions of SU(2) Yang-Mills-Higgs theory are constructed. They are asymptotically flat and represent gravitating monopole-monopole pairs. The solutions form two branches linked to the second Bartnik-McKinnon solution on upper mass branch and to the unstable monopole-monopole configuration in flat space on the lower branch, respectively.

gr-qc↗

arXiv2005

Electromagnetic Interaction in the System of Multimonopoles and Vortex Rings

Behavior of static axially symmetric monopole-antimonopole and vortex ring solutions of the SU(2) Yang-Mills-Higgs theory in an external uniform magnetic field is considered. It is argued that the axially symmetric monopole-antimonopole chains and vortex rings can be treated as a bounded electromagnetic system of the magnetic charges and the electric current rings. The magnitude of the external field is a parameter which may be used to test the structure of the static potential of the effective electromagnetic interaction between the monopoles with opposite orientation in the group space. It is shown that for a non-BPS solutions there is a local minimum of this potential.

hep-th↗

arXiv2005

SU(N) monopoles with and without SUSY

These are expanded notes of lectures given at the Advanced Summer School on Modern Mathematical Physics (JINR Dubna, July 2005) and at the 8th International School-Seminar ``The actual problems of microworld physics 2005'' (Gomel-Dubna, August 2005). I review classical monopole solutions of the SU(N) Yang-Mills-Higgs theory. The first part is a pedagogical introduction into to the theory of non-Abelian SU(2) monopoles. In the second part I discuss a particular case of SU(3) theories containing different limits of symmetry breaking. It turns out that the multimonopole configurations are natural in a model with the gauge group of higher rank. Here I discuss fundamental and composite monopoles and consider the limiting situation of the massless states. In the last part I briefly discuss construction of the $N = 2$ SU(2) supersymmetric monopoles and some of the basic properties which are connected with the field theoretical aspects of these classical solutions.

hep-th↗

arXiv2005

The Color--Flavor Transformation of induced QCD

The Zirnbauer's color-flavor transformation is applied to the $U(N_c)$ lattice gauge model, in which the gauge theory is induced by a heavy chiral scalar field sitting on lattice sites. The flavor degrees of freedom can encompass several `generations' of the auxiliary field, and for each generation, remaining indices are associated with the elementary plaquettes touching the lattice site. The effective, color-flavor transformed theory is expressed in terms of gauge singlet matrix fields carried by lattice links. The effective action is analyzed for a hypercubic lattice in arbitrary dimension. We investigate the corresponding d=2 and d=3 dual lattices. The saddle points equations of the model in the large-$N_c$ limit are discussed.

hep-lat↗

arXiv2004

Gravitating Monopole--Antimonopole Chains and Vortex Rings

We construct monopole-antimonopole chain and vortex solutions in Yang-Mills-Higgs theory coupled to Einstein gravity. The solutions are static, axially symmetric and asymptotically flat. They are characterized by two integers (m,n) where m is related to the polar angle and n to the azimuthal angle. Solutions with n=1 and n=2 correspond to chains of m monopoles and antimonopoles. Here the Higgs field vanishes at m isolated points along the symmetry axis. Larger values of n give rise to vortex solutions, where the Higgs field vanishes on one or more rings, centered around the symmetry axis. When gravity is coupled to the flat space solutions, a branch of gravitating monopole-antimonopole chain or vortex solutions arises, and merges at a maximal value of the coupling constant with a second branch of solutions. This upper branch has no flat space limit. Instead in the limit of vanishing coupling constant it either connects to a Bartnik-McKinnon or generalized Bartnik-McKinnon solution, or, for m>4, n>4, it connects to a new Einstein-Yang-Mills solution. In this latter case further branches of solutions appear. For small values of the coupling constant on the upper branches, the solutions correspond to composite systems, consisting of a scaled inner Einstein-Yang-Mills solution and an outer Yang-Mills-Higgs solution.

gr-qc↗

arXiv2004

New Regular Solutions with Axial Symmetry in Einstein-Yang-Mills Theory

We construct new regular solutions in Einstein-Yang-Mills theory. They are static, axially symmetric and asymptotically flat. They are characterized by a pair of integers (k,n), where k is related to the polar angle and $n$ to the azimuthal angle. The known spherically and axially symmetric EYM solutions have k=1. For k>1 new solutions arise, which form two branches. They exist above a minimal value of n, that increases with k. The solutions on the lower mass branch are related to certain solutions of Einstein-Yang-Mills-Higgs theory, where the nodes of the Higgs field form rings.

gr-qc↗

arXiv2004

Monopole-Antimonopole Chains and Vortex Rings

We consider static axially symmetric solutions of SU(2) Yang-Mills-Higgs theory. The simplest such solutions represent monopoles, multimonopoles and monopole-antimonopole pairs. In general such solutions are characterized by two integers, the winding number m of their polar angle, and the winding number n of their azimuthal angle. For solutions with n=1 and n=2, the Higgs field vanishes at m isolated points along the symmetry axis, which are associated with the locations of m monopoles and antimonopoles of charge n. These solutions represent chains of m monopoles and antimonopoles in static equilibrium. For larger values of n, totally different configurations arise, where the Higgs field vanishes on one or more rings, centered around the symmetry axis. We discuss the properties of such monopole-antimonopole chains and vortex rings, in particular their energies and magnetic dipole moments, and we study the influence of a finite Higgs self-coupling constant on these solutions.

hep-th↗

arXiv2004

Multimonopoles and closed vortices in SU(2) Yang-Mills-Higgs theory

We review classical monopole solutions of the SU(2) Yang-Mills-Higgs theory. The first part is a pedagogical introduction into to the basic features of the celebrated 't Hooft - Polyakov monopole. In the second part we describe new classes of static axially symmetric solutions which generalise 't Hooft - Polyakov monopole. These configurations are either deformations of the topologically trivial sector or the sectors with different topological charges. In both situations we construct the solutions representing the chains of monopoles and antimonopoles in static equilibrium. The solutions of another type are closed vortices which are centred around the symmetry axis and form different bound systems. Configurations of the third type are monopoles bounded with vortices. We suggest classification of these solutions which is related with 2d Poincare index.

hep-th↗

arXiv2004

Interaction of Vortices with an External Field

The interaction of a magnetic flux vortex with weak external fields is considered in the framework of the Abelian Higgs model. The approach is based on the calculation of the zero-mode excitation probability in the external field. The excitation of the field configuration is found perturbatively. As an example we consider the effect of interaction with an external current. The linear in the scalar field perturbation is also considered.

hep-th↗

arXiv2004

Properties of non-BPS SU(3) monopoles

This paper is concerned with magnetic monopole solutions of SU(3) Yang-Mills-Higgs system beyond the Bogomol'nyi-Prasad-Sommerfield limit. The different SU(2) embeddings, which correspond to the fundamental monopoles, as well the embedding along composite root are studied. The interaction of two different fundamental monopoles is considered. Dissolution of a single fundamental non-BPS SU(3) monopole in the limit of the minimal symmetry breaking is analysed.

hep-th↗