arXiv subjects

Dongsu Bak

Publications and source records attributed to Dongsu Bak.

At least 73 records · Page 4Linked to original sources

arXiv2006

Supersymmetric Q-Lumps in the Grassmannian nonlinear sigma models

We construct the N=2 supersymmetric Grassmannian nonlinear sigma model for the massless case and extend it to massive N=2 model by adding an appropriate superpotential. We then study their BPS equations leading to supersymmetric Q-lumps carrying both topological and Noether charges. These solutions are shown to be always time dependent even sometimes involving multiple frequencies. Thus we illustrate explicitly that the time dependence is consistent with remaining supersymmetries of solitons.

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arXiv2006

From static to evolving geometries -- R-charged hydrodynamics from supergravity

We show that one can obtain asymptotic evolving boost-invariant geometries in a simple manner from the corresponding static solutions. We exhibit the procedure in the case of a supergravity dual of R-charged hydrodynamics by turning on a supergravity gauge field and analyze the relevant thermodynamics. Finally we consider turning on the dilaton and show that electric and magnetic modes in the plasma equilibrate before reaching asymptotic proper times.

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arXiv2006

Dual of Big-bang and Big-crunch

Starting from the Janus solution and its gauge theory dual, we obtain the dual gauge theory description of the cosmological solution by procedure of the double anaytic continuation. The coupling is driven either to zero or to infinity at the big-bang and big-crunch singularities, which are shown to be related by the S-duality symmetry. In the dual Yang-Mills theory description, these are non singular at all as the coupling goes to zero in the N=4 Super Yang-Mills theory. The cosmological singularities simply signal the failure of the supergravity description of the full type IIB superstring theory.

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arXiv2005

M-theory Supertubes with Three and Four Charges

Using the covariant M5-brane action, we construct configurations corresponding to supertubes with three and four charges. We derive the BPS equations and study the full structure of the solutions. In particular, we find new solutions involving arbitrariness in field strengths.

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arXiv2005

1/2 BPS Geometries of M2 Giant Gravitons

We construct the general 1/2 BPS M2 giant graviton solutions asymptotic to the eleven-dimensional maximally supersymmetric plane wave background, based on the recent work of Lin, Lunin and Maldacena. The solutions have null singularity and we argue that it is unavoidable to have null singularity in the proposed framework, although the solutions are still physically relevant. They involve an arbitrary function F(x) which is shown to have a correspondence to the 1/2 BPS states of the BMN matrix model. A detailed map between the 1/2 BPS states of both sides is worked out.

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arXiv2005

All Higher Genus BPS Membranes in the Plane Wave Background

We consider supermembranes in the maximally supersymmetric plane wave geometry of the eleven dimensions and construct complete solutions of the continuum version of the 1/4 BPS equations. The supermembranes may have an arbitrary number of holes and arbitrary cross sectional shapes. In the matrix regularized version, we solve the matrix equations for several simple cases including fuzzy torus. In addition, we show that these solutions are trivially generalized to 1/8 and 1/16 BPS configuations.

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arXiv2005

Exactly Soluble BPS Black Holes in Higher Curvature N=2 Supergravity

We find a class of d=4, N=2 supergravity with $R^2$-interactions that admits exact BPS black holes. The prepotential contains quadratic, cubic and chiral curvature-squared terms. Black hole geometry realizes stretched horizon, and consists of anti-de Sitter, intermediate and outermost flat regions. Mass and entropy depends on charges and are modified not only by higher curvature terms but also by quadratic term in the prepotential. Consequently, even for large charges, entropy is no longer proportional to mass-squared.

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arXiv2005

Separation of Spontaneous Chiral Symmetry Breaking and Confinement via AdS/CFT Correspondence

We analyze, in the framework of AdS/CFT correspondence, the gauge theory phase structure that are supposed to be dual to the recently found non-supersymmetric dilatonic deformations to AdS_5 X S^5 in type IIB string theory. Analyzing the probe D7-brane dynamics in the backgrounds of our interest, which corresponds to the fundamental N=2 hypermultiplet, we show that the chiral bi-fermion condensation responsible for spontaneous chiral symmetry breaking is not logically related to the phenomenon of confinement.

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arXiv2004

Exactly Soluble Dynamics of (p,q) String Near Macroscopic Fundamental Strings

We study dynamics of Type IIB bound-state of a Dirichlet string and n fundamental strings in the background of N fundamental strings. Because of supergravity potential, the bound-state string is pulled to the background fundamental strings, whose motion is described by open string rolling radion field. The string coupling can be made controllably weak and, in the limit $1 << g^2_{\rm st} n << g^2_{\rm st} N$, the bound-state energy involved is small compared to the string scale. We thus propose rolling dynamics of open string radion in this system as an exactly solvable analog for rolling dynamics of open string tachyon in decaying D-brane. The dynamics bears a novel feature that the worldsheet electric field increases monotonically to the critical value as the bound-state string falls into the background string. Close to the background string, D string constituent inside the bound-state string decouples from fundamental string constituents.

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arXiv2004

Dilatonic Repulsons and Confinement via the AdS/CFT Correspondence

We study a class of dilatonic deformations of asymptotically AdS_5 X S^5 geometry analytically and numerically. The spacetime is non-supersymmetric and suffers from a naked singularity. We propose that the causality bound may serve as a criterion for such a geometry with a naked singularity to still make sense in the AdS/CFT correspondence. We show that the static string, the one corresponding to a large Wilson loop in the dual gauge theory, reveals confinement in a certain range of parameters of our solutions, where the singularity exhibits the repulsion that can well cloak the singularity from the static string probe. In particular, we find the exact expression for the tension of the QCD strings. We also discuss a possible interpretation of our solution in terms of unstable branes and their tachyon matter.

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arXiv2004

A Geometric Look on the Microstates of Supertubes

We give a geometric interpretation of the entropy of the supertubes with fixed conserved charges and angular momenta in two different approaches using the DBI action and the supermembrane theory. By counting the geometrically allowed microstates, it is shown that both the methods give consistent result on the entropy. In doing so, we make the connection to the gravity microstates clear.

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arXiv2004

Troubles with Spacetime Noncommutative Theories: Tachyons or S-branes?

We find Lorentzian solutions of spacetime noncommutative gauge theories that are localized exponentially in space and time. Together with time translational invariance of the theories, we argue that perurbative S matrix formulation of such theories is problematic in the sense that the S matrix based on free in and out states misses the spacetime localized degrees. We show that, in 3+1 dimensions, the problem disappears for the cases where the noncommutativity becomes purely spatial by an appropriate Lorentz transformation or the noncommutativity is lightlike with its electric and magnetic parts orthogonal to each other.

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arXiv2004

Holography, Dimensional Reduction and the Bekenstein Bound

We consider dimensional reduction of the lightlike holography of the covariant entropy bound from D+1 dimensional geometry of M X S to the D dimensional geometry M. With a warping factor, the local Bekenstein bound in D+1 dimensions leads to a more refined form of the bound from the D dimensional view point. With this new local Bekenstein bound, it is quite possible to saturate the lightlike holography even with nonvanishing expansion rate. With a Kaluza-Klein gauge field, the dimensional reduction implies a stronger bound where the energy momentum tensor contribution is replaced by the energy momentum tensor with the electromagnetic contribution subtracted.

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arXiv2004

Phase Moduli Space of Supertubes

We study possible deformations of BPS supertubes keeping their conserved charges fixed. We show that there is no flat direction to closed supertubes of circular cross section with uniform electric and magnetic fields, and also to open planar supertubes. We also find that there are continuously infinite flat deformations to supertubes of general shape under certain conditions.

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arXiv2003

Strong Evidence In Favor OF The Existence Of S-Matrix For Strings In Plane Waves

Field theories on the plane wave background are considered. We discuss that for such field theories one can only form 1+1 dimensional freely propagating wave packets. We analyze tree level four point functions of scalar field theory as well as scalars coupled to gauge fields in detail and show that these four point functions are well-behaved so that they can be interpreted as S-matrix elements for 2 particle $\to$ 2 particle scattering amplitudes. Therefore, at least classically, field theories on the plane wave background have S-matrix formulation.

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arXiv2003

Holography with Timelike Bulk Hypersurfaces

We propose a new version of holographic principle. This proposal extends the holographic principle based on the lightsheet to the one constraining the entropy passing through bulk hypersurface of timelike geodesics by the boundary area divided by 4G. We give a proof of the proposal in the classical regime based on a simple local entropy condition.

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arXiv2003

A Dilatonic Deformation of AdS_5 and its Field Theory Dual

We find a nonsupersymmetric dilatonic deformation of $AdS_5$ geometry as an exact nonsingular solution of the type IIB supergravity. The dual gauge theory has a different Yang-Mills coupling in each of the two halves of the boundary spacetime divided by a codimension one defect. We discuss the geometry of our solution in detail, emphasizing the structure of the boundary, and also study the string configurations corresponding to Wilson loops. We also show that that the background is stable under small scalar perturbations.

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arXiv2002

Supersymmetric Brane-Antibrane Systems: Matrix Model Description, Stability and Decoupling Limits

After reviewing the supertubes and super brane-antibrane systems in the context of matrix model, we look for more general higher-dimensional configurations. For D3-bar{D3}, we find a non-trivial configuration with E cdot B not equal to 0 and describe the worldvolume gauge theory. We present the string probe of D3-bar{D3} system and study the decoupling limits leading to either noncommutative Super-Yang-Mills or NCOS theories with eight supercharges.

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