Why adding a collinear magnetic field to the electric one on a D3 brane in a system of two parallel separated D3 branes can enhance the open string pair production? How is the open string pair production rate related to the QED ones in the weak field limit? We answer these questions and report the somehow expected but still remarkable relation between the weak field non-perturbative stringy rate and the corresponding QED ones in this letter.

Abstract Consider a system consisting of Dp and Dp′, placed parallel at a separation and with p − p′ = 2n (assuming p ≥ p′, the integer n ≥ 0 and p′ > 0). When either Dp or Dp′ carries a worldvolume electric flux, one in general expects a non-vanishing open string pair production due to the pair of virtual open string/anti open string connecting the two D branes under the action of the applied flux. However, this will not be true for p′ = 0 and p = 2, 4, 6 when the Dp carries a pure electric flux. In this note, we will explore the case for which a finite non-vanishing open string pair production rate can indeed be produced when a certain worldvolume flux is applied to the Dp brane and understand the physics behind.

To our best knowledge, the leading non-perturbative stringy interaction between an NS brane and a Dp brane remains unknown. We here present the non-perturbative stringy amplitudes for a system of an F-string and a Dp brane and a system of an NS 5 brane and a Dp brane for $0 \le p \le 6$. In either case, the F or NS5 and the Dp are placed parallel at a separation. We obtain the respective amplitudes, starting from the amplitude for a system of a D1 and a D3 for the former and that for a system of a D5 and a D3 system for the latter, based on the IIB S-duality and various T-dualities plus the consistency of both, along with the respective known long-range amplitudes. We would like to point out that the amplitude for the D1/D3 or D3/D5 computed from the usual D-brane technique does not take into consideration of the non-perturbative contribution due to the exchange of virtual closed D-string emitted by the D3. As such the resulting amplitudes obtained from this one via the S-duality and followed by various T-dualities are not consistent with the IIB S-duality. We resolve this issue and obtain the corresponding consistent amplitudes. The implications of so obtained amplitudes are also discussed.

Motivated by the recent work [1] by one of the present authors, we here report that there exist two new systems, namely, D3/(F, D1) and D3/(D3, (F, D1)), either of which can give rise to a much larger sizable open string pair production rate at a condition much relaxed. Here the D3 is taken as our own (1 + 3)-dimensional world while the non-threshold bound state (F, D1) or (D3, (F, D1)) is placed parallel nearby in the directions transverse to both our D3 world and the non-threshold bound state considered.

We present a detailed study of dynamically generating an M2 brane from super-gravitons (or D0 branes) in a pp-wave background possessing maximal spacetime SUSY. We have three kinds of dynamical solutions depending on the excess energy which appears as an order parameter signalling a critical phenomenon about the solutions. As the excess energy is below a critical value, we have two branches of the solution, one can have its size zero while the other cannot for each given excess energy. However there can be an instanton tunnelling between the two. Once the excess energy is above the critical value, we have a single solution whose dynamical behavior is basically independent of the background chosen and whose size can be zero at some instant. A by product of this study is that the size of particles or extended objects can grow once there is a non-zero excess energy even without the presence of a background flux, therefore lending support to the spacetime uncertainty principle.

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 peri-odically 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.

We compute the closed-string cylinder amplitude between one Dp brane and the other Dp′ brane, placed parallel at a separation, with each carrying a general constant worldvolume flux and with p−p′=0,2,4,6 and p≤6. For the p=p′, we show that the main part of the amplitude for p=p′<5 is a special case of that for p=p′=5 or 6 case. For all other p−p′=2,4,6 cases, we show that the amplitude is just a special case of the corresponding one for p=p′ case. Combined both, we obtain the general formula for the amplitude, which is valid for each of the cases considered and for arbitrary constant worldvolume fluxes. The corresponding general open string one-loop annulus amplitude is also obtained by a Jacobi transformation of the general cylinder one. We give also the general open string pair production rate. We study the properties of the amplitude such as the nature of the interaction, the open string tachyonic instability, and the possible open string pair production and its potential enhancement. In particular, in the presence of pure magnetic fluxes or magnetic-like fluxes, we find that the nature of interaction is correlated with the existence of potential open string tachyonic instability. When the interaction is attractive, there always exists an open string tachyonic instability when the brane separation reaches the minimum determined by the so-called tachyonic shift. When the interaction is repulsive, there is no such instability for any brane separation. We also find that the enhancement of open string pair production, in the presence of pure electric fluxes, can occur only for the p−p′=2 case.

This review article reports the recent studies, based on a series of publications by one of the present authors along with his collaborators, regarding the interaction between two D-branes, the open string pair production and its possible enhancement in Type II superstring theories. Specifically, computed is the interaction amplitude between two D-branes, placed parallel at a separation, with each carrying a general worldvolume constant flux, and discussed are the amplitude properties, say, the repulsive or attractive nature of the interaction. When at least one of the D-branes carries an electric flux, the interaction amplitude can have an imaginary part, reflecting the instability of the underlying system via the open string pair production. The decay rate and the pair production rate are both computed. In addition, the enhancement of the latter is found when the added electric and magnetic fluxes are correlated in both magnitude and direction in a certain manner. In particular, when one of the branes is D3 and the other is D1, the corresponding pair production rate becomes large enough to be tested in an earthbound laboratory. Note that the pair production rate is related to the brane separation along the direction transverse to both branes, therefore, to the extra-dimensions with respect to the brane observer. So if the underlying string theory is relevant and the D3 can be taken as our own 4-dimensional world, measuring, say, the electric current due to the pair production and comparing it against the added electric and magnetic fields to see if the measurements agree with the prediction of the computations. This can be used to verify the existence of extra-dimensions. Further, this provides also a potential new means to test the underlying string theory without the need of compactifying it to four dimensions.

In analogy to the Schwinger pair production in QED, there exists also the so-called open string pair production for a system of two Dp branes, placed parallel at a separation, with at least one brane carrying a worldvolume electric flux, in Type II string theories. There is however no such pair production if an isolated Dp brane carrying an electric flux is considered. The produced open strings are directly related to the brane separation, therefore to the extra-dimensions if taken from the viewpoint of a brane observer. This pair production can be greatly enhanced if one Dp brane carries also a magnetic flux. The largest pair production rate occurs for p=3, i.e., the D3 brane system, with the same applied fluxes. A detection of this pair production by the brane observer as the charged particle/anti-charged particle pair one may signal the existence of extra-dimensions and therefore provides a potential means to test the underlying string theories.

We here report a possibility of detecting the open string pair production from the system of a D3 brane, taken as our own (1 + 3)-dimensional world and carrying its worldvolume collinear electric and magnetic fluxes, and a nearby D-string, placed parallel at a separation in the directions transverse to both branes.

Recent studies by one of the present authors along with his collaborators in [1], [2], [3], [4] show that there exist the so-called open string pair production for a possible simplest system of two Dp branes, placed parallel at a separation and with each carrying different electric flux, in Type II superstring theories. Further this pair production can be greatly enhanced when a magnetic flux, sharing no common field strength index with the electric one, is added, implying then p≥3. Given this, one may wonder if further enhancement can be achieved by adding more magnetic flux(es) in a similar fashion. In this paper, we explore this possibility. It turns out that adding more such magnetic flux diminishes rather than enhances the pair production rate. This actually implies that the largest enhancement occurs at p=3 when the same realistic electric and magnetic fluxes are applied for all p≥3. Curiously one of D3 branes may be our own world and if so, the enhancement gives a possible opportunity to detect the pair production, therefore to test the underlying string theories.

We report a systematic study of the stringy interaction between two sets of Dp branes placed parallel at a separation in the presence of two worldvolume fluxes for each set. We focus in this paper on that the two fluxes on one set have the same structure as those on the other set but they in general differ in values, which can be both electric or both magnetic or one electric and one magnetic. We compute the respective stringy interaction amplitude and find that the presence of electric fluxes gives rise to the open string pair production while that of magnetic ones to the open string tachyon mode. The interplay of these two leads to the open string pair production enhancement in certain cases when one flux is electric and the other is magnetic. In particular, we find that this enhancement occurs even when the electric flux and the magnetic one share one common field strength index which is impossible in the one-flux case studied previously by the present author and his collaborator in [17]. This type of enhancement may have realistic physical applications, say, as a means to explore the existence of extra dimensions.

是否存在超出我们生活的4维时空的额外维度是一个有趣而重要的问题.本文从理论角度探讨这一问题,先讨论了早期引力与电磁相互作用统一的5维卡鲁扎-克莱茵(Kaluza-Klein,KK)-理论,然后介绍了超对称和超引力与额外维的关联,最后介绍了弦理论和M-理论,并解释为何超弦理论本身的完善要求存在一个时空维度最大可以是11维的M-理论.至少从经典层面上,额外维对超对称和超引力来说仅仅是一种选择,不是必须的.目前,除4维N=8超引力理论有可能是一个自洽的量子引力理论,其他4维和高维的超引力理论紫外都有问题,需要考虑新的物理自由度,对应的紫外完善理论很可能就是弦/M-理论.弦理论对额外维的要求有所不同,其微扰量子自洽性要求额外维必须存在.例如,对超弦理论,时空必须是10维的.如果弦/M-理论的确是描述物质和相互作用的基本理论,那额外维就一定存在,同时需要对额外的空间维度作紧致化,且其尺度必须小于目前的实验限制.本文也讨论了一些相关唯象大额外维理论.

We construct two new SL(2, ℤ) invariant vacua of type IIB string theory which are bound states of (p, q) strings with (m, n) 5-branes, written as ((F, D1), (NS5, D5)) and preserve 1/4 of the full space-time supersymmetries. For the first case, the strings live inside the 5-brane world-volume and in the second case the strings are perpendicular to the 5-brane world-volume. In the first case, naively one would expect an attractive interaction between the strings and the 5-branes due to attractive force between F and D5 and also between D1 and NS5. We find that 1/4 BPS bound state exists only when the vacuum moduli satisfy certain condition which is found to be consistent with the no-force condition between the branes. No such complication arises for the second case. The tension formulae and the various other descendant states which can be obtained by the application of T-duality for both these bound states are discussed.

We consider the stringy interaction between two parallel stacks of D3 branes placed at a separation. Each stack of D3 branes in a similar fashion carry an electric flux and a magnetic flux with the two sharing no common field strength index. The interaction amplitude has an imaginary part, giving rise to the Schwinger-like pair production of open strings. We find a significantly enhanced rate of this production when the two electric fluxes are almost identical and the brane separation is on the order of string scale. This enhancement will be largest if the two magnetic fluxes are opposite in direction. This novel enhancement results from the interplay of the non-perturbative Schwinger-type pair production due to the electric flux and the stringy tachyon due to the magnetic flux, and may have realistic physical applications.

基础研究是原始创新的源泉,没有基础和前沿领域的原始创新,科技创新就没有了根基.科学技术当前的地位和作用更为凸显,科学技术的发展从来没有像今天这样深刻地影响人类社会的方方面面,深刻地影响着人们的思想观念和生活方式,促进着人类社会的进步.本文将从科学发展的简单历史角度阐述自然科学规律的探索与科学技术的发展以及与促进人类社会进步的关联.

We study the thermodynamics and phase structures of the asymptotically flat dilatonic black holes in 4 dimensions, placed in a cavity 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.

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 world-volume 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.

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 generalized geometry renders manifest the SL(3)×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 GL(4,R)⋉R4 subgroup of the expected SL(5,R) U-duality symmetry is realized.

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. 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.