arXiv subjects

J. X. Lu

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

At least 37 records · Page 2Linked to original sources

arXiv2016

Dynamical brane creation and annihilation via a background flux

We study the dynamical Myers effect by allowing the fuzzy (or the dynamical dielectric brane) coordinates to be time dependent. We find three novel kinds of the dynamical spherical dielectric branes depending on their respective excess energies. The first represents a dynamical spherical brane carrying a negative excess energy (having a lower bound) with its radius oscillating periodically between two given non-zero values. The second is the one with zero excess energy and whose time dependence can be expressed in terms of a simple function. This particular dynamical spherical configuration represents the dielectric brane creation and/or annihilation like a photon in the presence of a background creating an electron-position pair and then annihilating back to a photon. The third is the one carrying positive excess energy and the radius can also oscillate periodically between two non-zero values but, unlike the first kind, it passes zero twice for each cycle. Each of the above can also be interpreted as the time evolution of a semi-spherical D-brane--anti semi-spherical D-brane system.

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arXiv2016

Phase structures of 4D stringy charged black holes in canonical ensemble

We study the thermodynamics and phase structures of the asymptotically flat dilatonic black holes in 4 dimensions, placed in a cavity {\it a la} York, in string theory for an arbitrary dilaton coupling. We consider these charged black systems in canonical ensemble for which the temperature at the wall of and the charge inside the cavity are fixed. We find that the dilaton coupling plays the key role in the underlying phase structures. The connection of these black holes to higher dimensional brane systems via diagonal (double) and/or direct dimensional reductions indicates that the phase structures of the former may exhaust all possible ones of the latter, which are more difficult to study, under conditions of similar settings. Our study also shows that a diagonal (double) dimensional reduction preserves the underlying phase structure while a direct dimensional reduction has the potential to change it.

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arXiv2015

Tachyon field theory description of (thermo)dynamics in dS space

In this work, we present a few pieces of evidence in support of a possible connection of the gravitational theory in dS space to the worldvolume theory of unstable D-branes. We show that the action describing the geodesic motion of a massive particle (or point-like object) in static dS space turns out to be the same as that of the tachyon field theory for an unstable particle. The motion along the radial direction from the origin, a locally Minkowski spacetime, to the horizon, a locally Rindler space times a sphere, represents just the tachyon condensation process, therefore providing a geometric picture of tachyon condensation. We further study a scalar in global or flat dS and the tachyon fluctuations in a homogeneous tachyon background, representing either the full or half S-brane, on unstable D-branes and find that certain dynamics of the dS universe corresponds to that of the homogeneous full or half S-brane. The thermal temperature of tachyon radiation is found to agree with that felt by any timelike observer in dS space. In string theory context, this temperature is just the Hagedorn one, signaling a phase transition to closed strings. An understanding of this transition in the bulk dS space is also given.

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arXiv2015

Membrane Duality Revisited

Just as string T-duality originates from transforming field equations into Bianchi identities on the string worldsheet, so it has been suggested that M-theory U-dualities originate from transforming field equations into Bianchi identities on the membrane worldvolume. However, this encounters a problem unless the target space has dimension $D = p + 1$. We identify the problem to be the nonintegrability of the U-duality transformation assigned to the pull-back map. Just as a double geometry renders manifest the $O(D,D)$ string T-duality, here we show in the case of the M2-brane in $D = 3$ that a generalised geometry renders manifest the $SL(3) \times SL(2)$ U-duality. In the case of M2-brane in $D=4$, with and without extra target space coordinates, we show that only the ${\rm GL}(4,R)\ltimes R^4$ subgroup of the expected $SL(5,R)$ U-duality symmetry is realised.

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arXiv2014

Modification of phase structure of black D6 branes in a canonical ensemble and its origin

It is well known that charged black $Dp$ branes of type II string theory share a universal phase structure of van der Waals$-$Maxwell liquid-gas type except $D5$ and $D6$ branes. Interestingly, the phase structure of $D5$ and $D6$ branes can be changed to the universal form with the inclusion of particular delocalized charged lower-dimensional branes. For $D5$ branes one needs to introduce delocalized $D1$ branes, and for $D6$ branes, one needs to introduce delocalized $D0$ branes to obtain the universal structure. In a previous paper [J. High Energy Phys. {\bf 04} (2013) 100] Lu with Wei study the phase structure of black $D6$ branes with the introduction of delocalized $D0$ branes in a special case when their charges are equal and the dilaton charge vanishes. In this paper, we look at the phase structure of the black $D6/D0$ system with the generic values of the parameters, which makes the analysis more involved but the structure more rich. We also provide reasons why the respective modifications of the phase structures to the universal form for the black $D5$ and $D6$ branes occur when specific delocalized lower-dimensional branes are introduced.

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arXiv2013

Modulating the phase structure of black D6 branes in canonical ensemble

There exists a dramatic difference in phase structure between charged black Dp-branes with $p < 5$ and charged black D5 or D6 branes. In [1], we found that the phase structure of charged black D5 system can be changed qualitatively to that of charged black Dp with $p < 5$ by adding the delocalized D1 branes but the similar change does not happen for the charged black D6 system through adding the delocalized D2 branes (Note that both D1/D5 and D2/D6 belong to the same type of D(p - 4)/Dp system). Adding the delocalized D4 branes to the black D6 branes doesn't work, either. In this paper, we consider adding the delocalized D0 branes, the only remaining lower dimensional branes, to the black D6 system for this purpose. We find that the delocalized charged black D0-branes alone share the same phase structure as the charged black D6 branes, having no van der Waals-Maxwell liquid-gas type. However, when the two are combined to form D0/D6, the resulting phase diagram finally gets changed dramatically to the wanted one, containing now the above liquid-gas type. This change arises from the interaction between D6 and the delocalized D0.

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arXiv2012

The phase structure of black D1/D5 (F/NS5) system in canonical ensemble

In this paper, we explore means which can be used to change qualitatively the phase structure of charged black systems. For this, we consider a system of black D1/D5 (or its S-dual F/NS5). We find that the delocalized charged black D-strings (F-strings) alone share the same phase structure as the charged black D5 branes (NS5-branes), having no van der Waals-Maxwell liquid-gas type. However, when the two are combined to form D1/D5 (F/NS5), the resulting phase diagram has been changed dramatically to a richer one, containing now the above liquid-gas type. The effect of adding the charged D-strings (F-strings) on the phase structure can also be effectively described as a slight increase of the transverse dimensions to the original D5 (NS5). This may be viewed as a connection between a brane charge and a fraction of spatial dimension at least in a thermodynamical sense.

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arXiv2011

Black holes and global structures of spherical spacetimes in Horava-Lifshitz theory

We systematically study black holes in the Horava-Lifshitz (HL) theory by following the kinematic approach, in which a horizon is defined as the surface at which massless test particles are infinitely redshifted. Because of the nonrelativistic dispersion relations, the speed of light is unlimited, and test particles do not follow geodesics. As a result, there are significant differences in causal structures and black holes between general relativity (GR) and the HL theory. In particular, the horizon radii generically depend on the energies of test particles. Applying them to the spherical static vacuum solutions found recently in the nonrelativistic general covariant theory of gravity, we find that, for test particles with sufficiently high energy, the radius of the horizon can be made as small as desired, although the singularities can be seen in principle only by observers with infinitely high energy. In these studies, we pay particular attention to the global structure of the solutions, and find that, because of the foliation-preserving-diffeomorphism symmetry, ${Diff}(M,{\cal{F}})$, they are quite different from the corresponding ones given in GR, even though the solutions are the same. In particular, the ${Diff}(M,{\cal{F}})$ does not allow Penrose diagrams. Among the vacuum solutions, some give rise to the structure of the Einstein-Rosen bridge, in which two asymptotically flat regions are connected by a throat with a finite non-zero radius. We also study slowly rotating solutions in such a setup, and obtain all the solutions characterized by an arbitrary function $A_{0}(r)$. The case $A_{0} = 0$ reduces to the slowly rotating Kerr solution obtained in GR.

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arXiv2011

The enriched phase structure of black branes in canonical ensemble

It is found that a necessary completion of phase structure of D-dimensional charged black p-brane ($p > 0$) in a cavity requires two additional thermodynamical phases, the so-called "bubble of nothing" and/or the extremal brane, in canonical ensemble. This finding resolves the puzzle about the missing phases which are needed for the underlying phase diagram when $\tilde d = D - p - 3 \leq 2$ and gives a new (bubble) phase which can become globally stable when $\tilde d > 2$. An analog of Hawking-Page transition is also found among other new phase transitions, giving a complete phase structure in this setup.

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arXiv2011

Phase structure of black branes in grand canonical ensemble

This is a companion paper of our previous work [1] where we studied the thermodynamics and phase structure of asymptotically flat black $p$-branes in a cavity in arbitrary dimensions $D$ in a canonical ensemble. In this work we study the thermodynamics and phase structure of the same in a grand canonical ensemble. Since the boundary data in two cases are different (for the grand canonical ensemble boundary potential is fixed instead of the charge as in canonical ensemble) the stability analysis and the phase structure in the two cases are quite different. In particular, we find that there exists an analog of one-variable analysis as in canonical ensemble, which gives the same stability condition as the rather complicated known (but generalized from black holes to the present case) two-variable analysis. When certain condition for the fixed potential is satisfied, the phase structure of charged black $p$-branes is in some sense similar to that of the zero charge black $p$-branes in canonical ensemble up to a certain temperature. The new feature in the present case is that above this temperature, unlike the zero-charge case, the stable brane phase no longer exists and `hot flat space' is the stable phase here. In the grand canonical ensemble there is an analog of Hawking-Page transition, even for the charged black $p$-brane, as opposed to the canonical ensemble. Our study applies to non-dilatonic as well as dilatonic black $p$-branes in $D$ space-time dimensions.

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arXiv2011

Phase transitions and critical behavior of black branes in canonical ensemble

We study the thermodynamics and phase structure of asymptotically flat non-dilatonic as well as dilatonic black branes in a cavity in arbitrary dimensions ($D$). We consider the canonical ensemble and so the charge inside the cavity and the temperature at the wall are fixed. We analyze the stability of the black brane equilibrium states and derive the phase structures. For the zero charge case we find an analog of Hawking-Page phase transition for these black branes in arbitrary dimensions. When the charge is non-zero, we find that below a critical value of the charge, the phase diagram has a line of first-order phase transition in a certain range of temperatures which ends up at a second order phase transition point (critical point) as the charge attains the critical value. We calculate the critical exponents at that critical point. Although our discussion is mainly concerned with the non-dilatonic branes, we show how it easily carries over to the dilatonic branes as well.

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arXiv2010

Remarks on the instability of black Dp-branes

We show that for black D$p$-branes having charge $Q$ and Hawking temperature $T$, the product $QT^{7-p}$ is bounded from above for $p\leq 5$ and is unbounded for $p=6$. While the maximum occurs at some finite value of a parameter for $p \leq 4$, it occurs at infinity of the parameter for $p=5$. As a consequence, for fixed charge, there are two black D$p$-branes (for $p\leq 4$) at any given temperature less than its maximum value, and when the temperature is maximum there is one black D$p$-brane. For $p=5$, there is only one black D5-brane at a given temperature less than its maximum value, whereas, for $p=6$, since there is no bound for the temperature, there is always a black D6-brane solution at a given temperature. Of the two black D$p$-branes (for $p\leq 4$), one is large which is shown to be thermodynamically unstable and the other is small which is stable. But for $p=5,6$, the black D$p$-branes are always thermodynamically unstable. The stable, small black D$p$-brane, however, under certain conditions, can become unstable quantum mechanically and decay either to a BPS D$p$-brane or to a Kaluza-Klein "bubble of nothing" through closed string tachyon condensation. The small D5, D6 branes, although classically unstable, have the same fate under similar conditions.

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arXiv2009

The D0$-$D8 system revisited

We address a few subtle issues regarding the interacting D0-D8 system. There are two existing interpretations for the counter-intuitive non-vanishing cylinder-diagram R-R potential. We improve them each by properly dealing with the divergence of potential in the R-R as well as the NS-NS sector, which has been ignored so far. We further test them by considering the D8 to carry a flux, electric or magnetic. We find that the improved interpretations continue to hold. We resolve a subtle issue regarding the regularization of fermionic zero-modes in the R-R sector when the D8 carries an electric flux so that a meaningful result for the potential can be calculated. The persistence of divergence for the potential in either sector in the presence of a flux on the D8 brane indicates that adding a flux/fluxes on the D8 brane doesn't help to improve its nature of existence as an independent object, therefore reenforcing the previous assertion on D8 branes.

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arXiv2009

The open string pair-production rate enhancement by a magnetic flux

We extend the amplitude calculations of \cite{Lu:2009yx} to exhaust the remaining cases for which one set of D$_p$ branes carrying a flux (electric or magnetic) is placed parallel at separation to the other set carrying also a flux but with the two fluxes sharing at most one common field-strength index. We then find that the basic structure of amplitudes remains the same when the two fluxes share at least one common index but it is more general when the two fluxes share no common index. We discuss various properties of the amplitudes such as the large separation limit, the onset of various instabilities and the open string pair production. In particular, when one flux is electric and weak and the other is magnetic and fixed, we find that the open string pair production rate is greatly enhanced by the presence of this magnetic flux when the two fluxes share no common field-strength index and this rate becomes significant when the separation is on the order of string scale.

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arXiv2009

Remarks on D_p and D_{p-2} with each carrying a flux

We explore various properties of interaction between D$_p$ and D$_{p'}$ with each carrying a worldvolume flux and with the $p'$-branes placed along $p'$ spatial worldvolume directions of the p-branes at a separation when $p - p' = 2$. Carefully analyzing the annulus amplitudes calculated via the boundary state approach, we find that many features of amplitudes remain similar to those studied when $p = p'$ such as the nature of force on the brane separation, the onset of various instabilities when the brane-separation is on the order of string scale and the occurrence of pair production of open strings when there is a relevant electric flux present. In addition, we have also found many new features of interaction which don't appear in the absence of fluxes or when $p = p'$ in the presence of fluxes, for examples, the nature of interaction can be repulsive and there is no onset of tachyonic instability under certain conditions. Even in the absence of a magnetic flux, we can have an exponential enhancement of the rate of pair production of open strings in certain cases, which may be significant enough to give observational consequences.

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arXiv2009

Non-supersymmetric D1/D5, F/NS5 and closed string tachyon condensation

We construct the intersecting non-supersymmetric (non-susy) D1/D5 solution of type IIB string theory. While, as usual, the solution is charged under an electric two-form and an electric six-form gauge field, it also contains a non-susy chargeless (non-BPS) D0-brane. The S-dual of this solution is the non-susy F/NS5 solution. We show how these solutions nicely interpolate between the corresponding black (or non-extremal) solutions and the Kaluza-Klein (KK) "bubble of nothing" (BON) by continuously changing some parameters characterizing the solutions from one set of values to another. We show, by a time symmetric general bubble initial data analysis, that the final bubbles in these cases are static and stable and the interpolations can be physically interpreted as closed string tachyon condensation. As special cases, we recover the transition of two charge black F-string to BON, considered by Horowitz, and also the transition from AdS$_3$ black hole to global AdS$_3$.

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arXiv2009

Interaction between two non-threshold bound states

A general non-threshold BPS (F, D$_p$) (or (D$_{p - 2}$, D$_p$)) bound state can be described by a boundary state with a quantized world-volume electric (or magnetic) flux and is characterized by a pair of integers $(m, n)$. With this, we calculate explicitly the interaction amplitude between two such non-threshold bound states with a separation $Y$ when each of the states is characterized by a pair of integers ($m_i, n_i$) with $i = 1, 2$. With this result, one can show that the non-degenerate (i.e., $m_i n_i \neq 0$) interaction is in general attractive for the case of (D$_{p - 2}$, D$_p$) but this is true and for certain only at large separation for the case of (F, D$_p$). In either case, this interaction vanishes only if $m_1/ n_1 = m_2/ n_2$ and $n_1 n_2 > 0$. We also study the analytic structure of the corresponding amplitude and calculate in particular the rate of pair production of open strings in the case of (F, D$_p$).

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arXiv2009

Intersecting non-SUSY branes and closed string tachyon condensation

Following \cite{Bai:2006vv} we here consider the supergravity solutions representing the charged non-supersymmetric $p$-brane (for $1\leq p \leq 6$) intersecting with chargeless non-supersymmetric 1-brane and 0-brane of type II string theories. We show how these solutions nicely interpolate between black $p$-branes and the Kaluza-Klein "bubble of nothing" (BON) by continuously varying some parameters characterizing the solutions from one set of values to another. By performing a time symmetric general bubble initial data analysis, we show that the interpolation implies a possible transition from black $p$-branes to KK BON only for $p\leq 4$, as in these cases there exist locally stable static bubbles under certain conditions. However, for $p>4$, black branes always decay into dynamical bubbles. Contrary to what is known in the literature, we argue that under certain conditions, the mechanism causing this transition to stable static bubbles can be the closed string tachyon condensation for all $p\leq 4$. We also show that the configurations indeed contain (chargeless) F-strings required for the closed string tachyons to appear causing the transitions to occur.

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