arXiv subjects

J. X. Lu

Publications and source records attributed to J. X. Lu.

At least 55 records · Page 3Linked to original sources

arXiv2009

On the low energy brane/anti-brane dynamics

We study the dynamical behavior of a pair of Dp-brane and anti Dp-brane ($0 \leq p \leq 6$) moving parallel to each other in the region where the brane and anti-brane annihilation will not occur and the low energy description is valid. Given this, we perform a general analysis, in the center of mass frame, of the behavior of the effective potential with respect to the relative brane separation and find that the classical orbits of this system are in general unbound except for $p = 6$ case for which classical bound orbits exist. The non-linearity of the low energy DBI action for D-brane is important for the underlying dynamics. We solve also the explicit orbits for $p = 6$ case.

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arXiv2007

On Brane-Antibrane Forces

In this note, we will discuss two aspects of brane-antibrane forces. In one aspect, we generalize the force calculation of D0-${\bar {\rm D}}$0 of Banks and Susskind to Dp-${\bar {\rm D}}p$ for $1\le p \leq 8$. In particular, we find that the force is also divergent for p = 1 while for the other cases ($p \ge 2$) the forces are in general finite when $Z \to 0^+$, where $Z = \frac{Y^2}{2π^2α'} - 1$ with Y, the brane-antibrane separation. However, the forces are divergent for all cases when Z < 0, signalling the occurrence of open string tachyon condensation in this regime. The other deals with the puzzling static nature of the supergravity brane-antibrane configurations. We will show that the force on a brane probe due to a brane-antibrane background vanishes when the probe is placed at the location of the coincident brane-antibranes, thereby providing a direct evidence for the existence of general static brane-antibrane configuration in the supergravity approximation.

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arXiv2006

The membrane at the end of the (de Sitter) universe

The original {\it membrane at the end of the universe} corresponds to a probe $M2$-brane of signature $(2,1)$ occupying the $S^{2} \times S^{1}$ boundary of the $(10,1)$ spacetime $AdS_{4} \times S^{7}$, and is described by an $OSp(4/8)$ SCFT. However, it was subsequently generalized to other worldvolume signatures $(s,t)$ and other spacetime signatures $(S,T)$. An interesting special case is provided by the $(3,0)$ brane at the end of the de Sitter universe $dS_{4}$ which has recently featured in the $dS/CFT$ correspondence. The resulting CFT contains the one recently proposed as the holographic dual of a four-dimensional de Sitter cosmology. Supersymmetry restricts $S,T,s,t$ by requiring that the corresponding bosonic symmetry $O(s+1,t+1) \times O(S-s,T-t)$ be a subgroup of a superconformal group. The case of $dS_{4} \times AdS_{7}$ is `doubly holographic' and may be regarded as the near horizon geometry of $N_{2}$ $M2$-branes or equivalently, under interchange of conformal and R symmetry, of $N_{5}$ $M5$-branes, provided $N_{2}=2N_{5}{}^{2}$. The same correspondence holds in the pp-wave limit of conventional $M$-theory.

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arXiv2006

Non-SUSY $p$-branes, bubbles and tubular branes

We consider non-supersymmetric $p$-brane solutions of type II string theories characterized by three parameters. When the charge parameter vanishes and one of the other two takes a specific value, the corresponding chargeless solutions can be regular and describe ``bubbles'' in static (unstable) equilibrium when lifted to $d = 11$. In appropriate coordinates, they represent D6 branes with a tubular topology R$^{1,p}$ $\times$ S$^{6-p}$ when reduced to $d=10$, called the tubular D6 branes, held in static equilibrium by a fixed magnetic flux (fluxbrane). Moreover, a `rotation parameter' can be introduced to either of the above two eleven dimensional configurations, giving rise to a generalized configuration labelling by the parameter. As such, it brings out the relations among non-supersymmetric $p$-branes, bubbles and tubular D6 branes. Given our understanding on tubular D6 branes, we are able to reinforce the interpretation of the chargeless non-supersymmetric $p$-branes as representing $p$-brane-anti$p$-brane (or non-BPS $p$-brane) systems, and understand the static nature and various singularities of these systems in a classical supergravity approximation.

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arXiv2006

Fundamental strings and NS5-branes from unstable D-branes in supergravity

By using the non-supersymmetric $p$-brane solutions delocalized in arbitrary number of transverse directions in type II supergravities, we show how they can be regarded as interpolating solutions between unstable D$p$-branes (a non-BPS D-brane or a pair of coincident D-brane-antiD-brane) and fundamental strings and also between unstable D$p$-branes and NS5-branes. We also show that some of these solutions can be regarded as interpolating solutions between NS5/$\bar{\rm NS}$5 and D$p$-branes (for $p \leq 5$). This gives a closed string description of the tachyon condensation and lends support to the conjecture that the open string theory on unstable D-branes at the tachyonic vacuum has soliton solutions describing not only the lower dimensional BPS D-branes, but also the fundamental strings as well as the NS5-branes.

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arXiv2005

Tachyon condensation on the intersecting brane-antibrane system

We generalize our study of the tachyon condensation on the brane-antibrane system [hep-th/0403147] to the intersecting brane-antibrane system. The supergravity solutions of the intersecting brane-antibrane system are characterized by five parameters. We relate these parameters to the microscopic physical parameters, namely, the number of D$p$-branes ($N_1$), the number of ${\bar {\rm D}}p$-branes (${\bar N}_1$), the number of D$(p-4)$-branes ($N_2)$, the number of ${\bar{\rm D}}(p-4)$-branes (${\bar N}_2$) and the tachyon vev $T$. We show that the solution and the ADM mass capture all the required properties and give a correct description of the tachyon condensation for the intersecting brane-antibrane system.

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arXiv2005

Non-SUSY $p$-branes delocalized in two directions, tachyon condensation and T-duality

We here generalize our previous construction [hep-th/0409019] of non-supersymmetric $p$-branes delocalized in one transverse spatial direction to two transverse spatial directions in supergravities in arbitrary dimensions ($d$). These solutions are characterized by five parameters. We show how these solutions in $d=10$ interpolate between D($p+2$)-anti-D($p+2$) brane system, non-BPS D$(p+1)$-branes (delocalized in one direction) and BPS D$p$-branes by adjusting and scaling the parameters in suitable ways. This picture is very similar to the descent relations obtained by Sen in the open string effective description of non-BPS D$(p+1)$ brane and BPS D$p$-brane as the respective tachyonic kink and vortex solutions on the D$(p+2)$-anti-D$(p+2)$ brane system (with some differences). We compare this process with the T-duality transformation which also has the effect of increasing (or decreasing) the dimensionality of the branes by one.

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arXiv2004

Delocalized, non-SUSY $p$-branes, tachyon condensation and tachyon matter

We construct non-supersymmetric $p$-brane solutions of type II supergravities in arbitrary dimensions ($d$) delocalized in one of the spatial transverse directions. By a Wick rotation we convert these solutions into Euclidean $p$-branes delocalized in the transverse time-like direction. The former solutions in $d=10$ nicely interpolate between the $(p+1)$-dimensional non-BPS D-branes and the $p$-dimensional BPS D-branes very similar to the picture of tachyon condensation for the tachyonic kink solution on the non-BPS D-branes. On the other hand the latter solutions interpolate between the $(p+1)$-dimensional non-BPS D-branes and the tachyon matter supergravity configuration very similar to the picture of rolling tachyon on the non-BPS D-branes.

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arXiv2004

Static, non-SUSY $p$-branes in diverse dimensions

We give explicit constructions of static, non-supersymmetric $p$-brane (for $p \leq d-4$, where $d$ is the space-time dimensionality and including $p=-1$ or D-instanton) solutions of type II supergravities in diverse dimensions. A subclass of these are the static counterpart of the time dependent solutions obtained in [hep-th/0309202]. Depending on the forms of the non-extremality function $G(r)$ defined in the text, we discuss various possible solutions and their region of validity. We show how one class of these solutions interpolate between the $p$-brane--anti $p$-brane solutions and the usual BPS $p$-brane solutions in $d=10$, while the other class, although have BPS limits, do not have such an interpretation. We point out how the time dependent solutions mentioned above can be obtained by a Wick rotation of one class of these static solutions. We also discuss another type of solutions which might seem non-supersymmetric, but we show by a coordinate transformation that they are nothing but the near horizon limits of the various BPS $p$-branes already known.

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arXiv2004

Supergravity approach to tachyon condensation on the brane-antibrane system

We study the tachyon condensation on the D-brane--antiD-brane system from the supergravity point of view. The non-supersymmetric supergravity solutions with symmetry ISO($p,1$) $\times$ SO($9-p$) are known to be characterized by three parameters. By interpreting this solution as coincident $N$ D$p$-branes and ${\bar N}$ ${\bar {\rm D}}p$-branes we give, for the first time, an explicit representation of the three parameters of supergravity solutions in terms of $N, \bar N$ and the tachyon vev. We demonstrate that the solution and the corresponding ADM mass capture all the required properties and give a correct description of the tachyon condensation advocated by Sen on the D-brane--antiD-brane system.

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arXiv2004

On the Construction of SL(2,Z) Type IIB 5-Branes

This talk reviews our recent work on the construction of SL(2,Z) multiplets of type IIB superfivebranes. We here pay particular attention to the methods employed and some salient features of the solutions.

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arXiv2001

(1 + p)-Dimensional Open D(p - 2) Brane Theories

The dynamics of a Dp brane can be described either by an open string ending on this brane or by an open D(p - 2) brane ending on the same Dp brane. The ends of the open string couple to a Dp brane worldvolume gauge field while the boundary of the open D(p - 2) brane couples to a (p - 2)-form worldvolume potential whose field strength is Poincare dual to that of the gauge field on the Dp-brane worldvolume. With this in mind, we find that the Poincare dual of the fixed rank-2 magnetic field used in defining a (1 + p)-dimensional noncommutative Yang-Mills (NCYM) gives precisely a near-critical electric field for the open D(p - 2) brane. We therefore find (1 + p)-dimensional open D(p - 2) brane theories along the same line as for obtaining noncommutative open string theories (NCOS), OM theory and open Dp brane theories (ODp) from NS5 brane. Similarly, the Poincare dual of the near-critical electric field used in defining a (1 + p)-dimensional NCOS gives a fixed magnetic-like field. This field along with the same bulk field scalings defines a (1 + p)-dimensional noncommutative field theory. In the same spirit, we can have various (1 + 5)-dimensional noncommutative field theories resulting from the existence of ODp if the description of open D(4 - p) brane ending on the NS5 brane is insisted.

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arXiv2001

The Galilean Nature of V-duality for Noncommutative Open String and Yang-Mills Theories

A V-duality conjecture for noncommutative open string theories (NCOS) that result from decoupling D-branes in Lorentz-boost related backgrounds was put forward recently in hep-th/0006013. The aim of this paper is to test the Galilean nature of this conjecture in the gravity dual setup. We start with an (F, D3) bound state Lorentz-boosted along one D3-brane direction perpendicular to the F-string, and show that insisting a decoupled NCOS allows only infinitesimal Lorentz boosts. In this way, it is shown that the V-duality relates a family of NCOS by Galileo boosts. Starting with a Lorentz-boosted (D1,D3) bound state, we show that a similar V-duality works for noncommutative Yang-Mills (NCYM) theories as well. In addition, we deduce by a holography argument that the running string tension, as a function of the energy scale, for NCOS (or NCYM) remains unchanged under V-duality.

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arXiv2001

OM Theory and V-duality

We show that the (M5, M2, M2$'$, MW) bound state solution of eleven dimensional supergravity recently constructed in hep-th/0009147 is related to the (M5, M2) bound state one by a finite Lorentz boost along a M5-brane direction perpendicular to the M2-brane. Given the (M5, M2) bound state as a defining system for OM theory and the above relation between this system and the (M5, M2, M2', MW) bound state, we test the recently proposed V-duality conjecture in OM theory. Insisting to have a decoupled OM theory, we find that the allowed Lorentz boost has to be infinitesimally small, therefore resulting in a family of OM theories related by Galilean boosts. We argue that such related OM theories are equivalent to each other. In other words, V-duality holds for OM theory as well. Upon compactification on either an electric or a `magnetic' circle (plus T-dualities as well), the V-duality for OM theory gives the known one for either noncommutative open string theories or noncommutative Yang-Mills theories. This further implies that V-duality holds in general for the little m-theory without gravity.

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arXiv2000

((F, D1), D3) bound state, S-duality and noncommutative open string/Yang-Mills theory

We study decoupling limits and S-dualities for noncommutative open string/ Yang-Mills theory in a gravity setup by considering an $SL(2,Z)$ invariant supergravity solution of the form ((F, D1), D3) bound state of type IIB string theory. This configuration can be regarded as D3-branes with both electric and magnetic fields turned on along one of the spatial directions of the brane and preserves half of the space-time supersymmetries of the string theory. Our study indicates that there exists a decoupling limit for which the resulting theory is an open string theory defined in a geometry with noncommutativity in both space-time and space-space directions. We study S-duality of this noncommutative open string (NCOS) and find that the same decoupling limit in the S-dual description gives rise to a space-space noncommutative Yang-Mills theory (NCYM). We also discuss independently the decoupling limit for NCYM in this D3 brane background. Here we find that S-duality of NCYM theory does not always give a NCOS theory. Instead, it can give an ordinary Yang-Mills with a singular metric and an infinitely large coupling. We also find that the open string coupling relation between the two S-duality related theories is modified such that S-duality of a strongly coupled open-string/Yang-Mills theory does not necessarily give a weakly coupled theory. The relevant gravity dual descriptions of NCOS/NCYM are also given.

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arXiv2000

On the relationship of gravitational constants in KK reduction

In this short note, we try to clarify a seemly trivial but often confusing question in relating a higher-dimensional physical gravitational constant to its lower-dimensional correspondence in Kaluza-Klein reduction. In particular, we re-derive the low-energy M-theory gravitational constant in terms of type IIA string coupling $g_s$ and constant $α'$ through the metric relation between the two theories.

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arXiv2000

SL(2, Z) Duality and 4-Dimensional Noncommutative Theories

We investigate how the four-dimensional noncommutative open string/Yang-Mills theory behaves under a general non-perturbative quantum $SL(2,Z)$ symmetry transformation. We discuss this by considering D3 branes in a constant background of axion, dilaton, and electric and magnetic fields (including both $ {\bf E} \perp {\bf B}$ and {\bf E}$||${\bf B} cases) in the respective decoupling limit. We find that the value of axion, whether rational or irrational, determines the nature of the resulting theory under $SL(2,Z)$ as well as its properties such as the coupling constant and the number of noncommutative directions. In particular, a strongly coupled theory with an irrational value of axion can never be physically equivalent to a weakly coupled theory while this is usually true for a theory with a rational value of axion. A noncommutative Yang-Mills (NCYM) (resulting from D3 branes with pure magnetic flux) is physically equivalent to a noncommutative open string (NCOS) but if the value of axion is irrational, we also have noncommutative space-space directions in addition to the usual noncommutative space-time directions for NCOS. We also find in general that a NCOS cannot be physically equivalent to a NCYM but to another NCOS if the value of axion is irrational. We find another new decoupling limit for possible light-like NCYM whose $SL(2,Z)$ duality is a light-like ordinary Yang-Mills if the value of the axion is rational. Various related questions are also discussed.

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arXiv2000

(p + 1)-Dimensional Noncommutative Yang-Mills and D($p - 2$) Branes

We consider systems of non-threshold bound states (D(p$-$2), Dp), for $2\le p \le 6$, in type II string theories. Each of them can be viewed as Dp branes with a nonzero (rank two) Neveu-Schwarz $B$ field. We study the noncommutative effects in the gravity dual descriptions of noncommutative gauge theories for these systems in the limit where the brane worldvolume theories decouple from gravity. We find that the noncommutative effects are actually due to the presence of infinitely many D(p$-$2) branes in the (D(p$-$2), Dp) system which play the dominant role over the Dp branes in the large $B$-field limit. Our study indicates that Dp branes with a constant $B$-field represents dynamically the system of infinitely many D(p$-$2) branes without $B$-field in the decoupling limit. This implies an equivalence between the noncommutative Yang-Mills in $(p + 1)$-dimensions and an ordinary Yang-Mills with gauge group $U (\infty)$ in $(p - 1)$-dimensions. We provide a physical explanation for the new scale which measures the noncommutativity.

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