arXiv subjects

Bum-Hoon Lee

Publications and source records attributed to Bum-Hoon Lee.

At least 145 records · Page 8Linked to original sources

arXiv2008

Geodesic Properties and Orbits in 5-dimensional Hypercylindrical Spacetime

We investigate the geodesic motions of a massive particle and light ray in the hyperplane orthogonal to the symmetry axis in the 5-dimensional hypercylindrical spacetime. The class of the solutions depends on one constant a which is the ratio of string mass density and tension. There exist unstable orbits in null geodesic only in some range of a. The innermost stable circular orbits in timelike geodesic also exist only in a certain range of the parameter a. The capture cross section and the deflection angle of light ray are also computed.

gr-qc↗

arXiv2008

Spiky Strings on AdS(4) X CP**3

We study a giant magnon and a spike solution for the string rotating on AdS(4) X CP**3 geometry. We consider rigid rotating fundamental string in the SU(2) X SU(2) sector inside the CP**3 and find out the general form of all the conserved charges. We find out the dispersion relation corresponding to both the known giant magnon and the new spike solutions. We further study the finite size correction in both cases.

hep-th↗

arXiv2008

M-brane bound states and the supersymmetry of BPS solutions in the Bagger-Lambert theory

We continue our study of BPS equations and supersymmetric configurations in the Bagger-Lambert theory. The superalgebra allows three different types of central extensions which correspond to compounds of various M-theory objects: M2-branes, M5-branes, gravity waves and Kaluza-Klein monopoles which intersect or have overlaps with the M2-branes whose dynamics is given by the Bagger-Lambert action. As elementary objects they are all 1/2-BPS, and multiple intersections of $n$-branes generically break the supersymmetry into $1/2^n$, as it is well known. But a particular composite of M-branes can preserve from 1/16 up to 3/4 of the original ${\cal N}=8$ supersymmetries as previously discovered. In this paper we provide the M-theory interpretation for various BPS equations, and also present explicit solutions to some 1/2-BPS equations.

hep-th↗

arXiv2008

Magnon like solutions for strings in I-brane background

We study the solutions for fundamental string rotating in a background generated by a 1+1 dimensional intersection of two orthogonal stacks of fivebranes in type IIB string theory. We show the existence of magnon like solutions for the string moving simultaneously in the two spheres in this background and find the relevant dispersion relation among the various conserved charges.

hep-th↗

arXiv2008

On the giant magnon and spike solutions for strings on AdS$_3\times$ S$^3$

We study solutions for the rotating strings on the sphere with a background NS-NS field and on the Anti-de-Sitter spacetime. We show the existence of magnon and single spike solutions on R$\times$S$^2$ in the presence of constant magnetic field as two limiting cases. We also study the solution for strings on AdS$_3\times$ S$^3$ with Melvin deformation. The dispersion relations among various conserved charges are shown to receive finite corrections due to the deformation parameter. We further study the rotating string on AdS$_3 \times$ S$^3$ geometry with two conserved angular momenta on S$^3$ and one spin along the AdS$_3$. We show that there exists two kinds of solutions: a circular string solution and a helical string. We find out the dispersion relation among various charges and give physical interpretation of these solutions.

hep-th↗

arXiv2008

Dynamics of false vacuum bubbles with nonminimal coupling

We study the dynamics of false vacuum bubbles. A nonminimally coupled scalar field gives rise to the effect of negative tension. The mass of a false vacuum bubble from outside observer's point of view can be positive, zero, or negative. The interior false vacuum has de Sitter geometry, while the exterior true vacuum background can have geometry depending on the vacuum energy. We show that there exist expanding false vacuum bubbles without the initial singularity in the past.

hep-th↗

arXiv2008

Marginal Deformations as Lower Dimensional D-brane Solutions in Open String Field theory

By direct calculation we showed that a finite analytic solution for marginal deformation of open string field theory, by a matter primary operator with singular OPE, can be obtained to all orders in the deformation parameter. In particular, we obtained solutions that describe lower dimensional D-branes and our results agree with the results obtained when the same problem is treated in the world-sheet conformal field theory language.

hep-th↗

arXiv2007

Fluctuations around the Tachyon Vacuum in Open String Field Theory

We consider quadratic fluctuations around the tachyon vacuum numerically in open string field theory. We work on a space ${\cal H}_N^{\rm vac}$ spanned by basis string states used in the Schnabl's vacuum solution. We show that the truncated form of the Schnabl's vacuum solution on ${\cal H}_N^{\rm vac}$ is well-behaved in numerical work. The orthogonal basis for the new BRST operator $\tilde Q$ on ${\cal H}_N^{\rm vac}$ and the quadratic forms of potentials for independent fields around the vacuum are obtained. Our numerical results support that the Schnabl's vacuum solution represents the minimum energy solution for arbitrary fluctuations also in open string field theory.

hep-th↗

arXiv2007

Gluon Condensation at Finite Temperature via AdS/CFT

We consider gluon condensation (GC) at finite temperature using AdS/CFT. We first show that in the presence of regular horizon, the GC is forbidden in high temperature. Then we consider gravity back-reaction to dilaton coupling and show that the back-reaction develops an singularity, and non-vanishing value of gluon condensation is allowed. We also study thermodynamic quantities and the trace anomaly in the presence of the GC. We discuss how to define a temperature in the presence of the singularity which forbids Hawking temperature. Finally we describe the thermodynamics of the gluon condensation including the effect of the Hawking-Page transition.

hep-th↗

arXiv2007

Holographic trace anomaly at finite temperature

We find an exact coordinate transformation rule from the $AdS_5$ Schwarzschild black hole in the Poincare and the global patch to the Fefferman-Graham coordinate system. Using these results, we evaluate the corresponding holographic stress tensor and trace anomaly of the boundary theory as a function of the radial coordinate. Following the AdS/CFT correspondence, we reinterpret the radial coordinate dependence of the trace anomaly as the Wilsonian renormalization group(RG) flow of the boundary theory.

hep-th↗

arXiv2007

Deconfinement phase transition in holographic QCD with matter

In the framework of a holographic QCD approach we study an influence of matters on the deconfinement temperature, $T_c$. We first consider quark flavor number ($N_f$) dependence of $T_c$. We observe that $T_c$ decreases with $N_f$, which is consistent with a lattice QCD result. We also delve into how the quark number density $ρ_q$ affects the value of $T_c$. We find that $T_c$ drops with increasing $ρ_q$. In both cases, we confirm that the contributions from quarks are suppressed by $1/N_c$, as it should be, compared to the ones from a gravitational action (pure Yang-Mills).

hep-ph↗

arXiv2007

Domain wall cosmology and multiple accelerations

We classify the cosmological behaviors of the domain wall under junctions between two spacetimes in terms of various parameters: cosmological constants of bulk spacetime, a tension of a domain wall, and mass parameters of the black hole-type metric. Especially, we consider the false-true vacuum type junctions and the domain wall connecting between an inner AdS space and an outer AdS Reissner-Nordstr${\rm \ddot{o}}$m black hole. We find that there exist a solution to the junction equations with an inflation at earlier times and an accelerating expansion at later times.

hep-th↗

arXiv2006

The false vacuum bubble nucleation due to a nonminimally coupled scalar field

We study the possibility of forming the false vacuum bubble nucleated within the true vacuum background via the true-to-false vacuum phase transition in curved spacetime. We consider a semiclassical Euclidean bubble in the Einstein theory of gravity with a nonminimally coupled scalar field. In this paper we present the numerical computations as well as the approximate analytical computations. We mention the evolution of the false vacuum bubble after nucleation.

hep-th↗

arXiv2005

More on supersymmetric D-branes in type IIB plane wave background

We extend the study on D-branes in the type IIB plane wave background to less supersymmetric configurations. We show that many new supersymmetric D-branes can be found by turning on electric as well as magnetic background fluxes, or constantly boosting D-branes.

hep-th↗

arXiv2005

Two Point Correlation Function of Sine-Liouville Theory

Exact two point correlation functions of sine-Liouville theory are presented for primary fields with U(1) charge neutral, which may either preserve or break winding number. Our result is checked with perturbative calculation and is also consistent with previous one which can be obtained by restricting the action parameters.

hep-th↗

arXiv2004

Supersymmetric D-branes in Type IIB Plane Wave Background

We systematically analyze supersymmetric D-branes in the type IIB plane wave background using Green-Schwarz superstring theory. We find several new supersymmetric oblique and curved D-branes. The supersymmetries preserved by various configurations of these D-branes including their intersections are also identified. In particular, we show that $D_+$-branes of type (+,-,n,n) for n=1,2,3,4 preserve 4 dynamical supersymmetries by introducing gauge field excitations and newly discovered oblique D5- and D7-branes also preserve four or two dynamical supersymmetries with gauge field condensates. Furthermore we find new curved D-branes preserving four dynamical supersymmetries.

hep-th↗

arXiv2003

Intersecting D-branes in Type IIB Plane Wave Background

We study intersecting D-branes in a type IIB plane wave background using Green-Schwarz worldsheet formulation. We consider all possible $D_\pm$-branes intersecting at angles in the plane wave background and identify their residual supersymmetries. We find, in particular, that $D_\mp - D_\pm$ brane intersections preserve no supersymmetry. We also present the explicit worldsheet expressions of conserved supercharges and their supersymmetry algebras.

hep-th↗

arXiv2003

Superstrings and D-branes in A Plane Wave

We carefully analyze the supersymmetry algebra of closed strings and open strings in a type IIB plane wave background. We use eight component chiral spinors, SO(8) Majorana-Weyl spinors, in light-cone gauge to provide a useful basis of string field theory calculation in the plane wave. We consider the two classes of D-branes, $D_\pm$-branes, and give a worldsheet derivation of conserved supercurrents for all half BPS D-branes preserving 16 supersymmetries in the type IIB plane wave background. We exhaustively provide the supersymmetry algebra of the half BPS branes as well. We also point out that the supersymmetry algebra distinguishes the two SO(4) directions with relative sign which is consistent with the Z_2 symmetry of the string action.

hep-th↗