D-brane Dynamics Research Articles

EXOTIC SMOOTH ℝ4AND CERTAIN CONFIGURATIONS OF NS AND D BRANES IN STRING THEORY

In this paper, we show that in some important cases, four-dimensional data can be extracted from superstring theory such that (i) the data are Euclidean four-geometries embedded in standard ℝ4, (ii) these data depend on NS and D brane charges of some string backgrounds, (iii) it is of potential relevance to four-dimensional physics, (iv) the compactification and stabilization techniques are not in use, but are rather replaced. We analyze certain configurations of NS and D-branes in the context of SU(2) WZW model and find the correlations with different exotic smoothings of ℝ4. First, the dynamics of D-branes in SU(2) WZW model at finite k, i.e. the charges of the branes, refers to the exoticness of ambient ℝ4. Next, the correspondence between exotic smoothness on four-space, transversal to the world volume of NS5 branes in type IIA, and the number of these NS5 branes follows. Finally, the translation of ten-dimensional string backgrounds to Euclidean four-spaces embedded as open subsets in the standard ℝ4is achieved.

Non-perturbative vacuum destabilization and D-brane dynamics

We analyze the process of string vacuum destabilization due to instanton induced superpotential couplings which depend linearly on charged fields. These nonperturbative instabilities result in potentials for the D-brane moduli and lead to processes of D-brane recombination, motion and partial moduli stabilization at the non-perturbative vacuum. By using techniques of D-brane instanton calculus, we explicitly compute this scalar potential in toroidal orbifold compactifications with magnetized D-branes by summing over the possible discrete instanton configurations. We illustrate explicitly the resulting dynamics in globally consistent models. These instabilities can have phenomenological applications to breaking hidden sector gauge groups, open string moduli stabilization and supersymmetry breaking. Our results suggest that breaking supersymmetry by Polonyi-like models in string theory is more difficult than expected.

Nuclear matter to strange matter transition in holographic QCD

We construct a simple holographic QCD model to study nuclear matter to strange matter transition. The interaction of dense medium and hadrons is taken care of by imposing the force balancing condition for stable D4/D6/D6 configuration. By considering the intermediate and light flavor branes interacting with baryon vertex homogeneously distributed along R^3 space and requesting the energy minimization, we find that there is a well defined transition density as a function of current quark mass. We also find that as density goes up very high, intermediate (or heavy) and light quarks populate equally as expected from the Pauli principle. In this sense, the effect of the Pauli principle is realized as dynamics of D-branes.

Quintessence and phantom dark energy from ghostD-branes

We present a novel dark-energy candidate, based upon the existence and dynamics of ghost D-branes in a warped compactification of type IIB string theory. Gp-branes cancel the combined BPS sectors of the Dp-branes, while they preserve the same supersymmetries. We show that this scenario can naturally lead to either quintessence or phantomlike behaviors, depending on the form of the involved potentials and brane tension. As a specific example we investigate the static, dark-energy dominated solution subclass.

Open string wavefunctions in warped compactifications

We analyze the wavefunctions for open strings in warped compactifications, and compute the warped Kähler potential for the light modes of a probe D-brane. This analysis not only applies to the dynamics of D-branes in warped backgrounds, but also allows to deduce warping corrections to the closed string Kähler metrics via their couplings to open strings. We consider in particular the spectrum of D7-branes in warped Calabi-Yau orientifolds, which provide a string theory realizations of the Randall-Sundrum scenario. We find that certain background fluxes, necessary in the presence of warping, couple to the fermionic wavefunctions and qualitatively change their behavior. This modified dependence of the wavefunctions are needed for consistency with supersymmetry, though it is present in non-supersymmetric vacua as well. We discuss the deviations of our setup from the RS scenario and, as an application of our results, compute the warping corrections to Yukawa couplings in a simple model. Our analysis is performed both with and without the presence of D-brane world-volume flux, as well as for the case of backgrounds with varying dilaton.

Dynamics and stability of light-like tachyon condensation

Recently, Hellerman and Schnabl considered the dynamics of unstable D-branes in the background of a linear dilaton. Remarkably, they were able to construct light-like tachyon solutions which interpolate smoothly between the perturbative and nonperturbative vacua, without undergoing the wild oscillations that plague time-like solutions. In their analysis, however, the full structure of the initial value problem for the nonlocal dynamical equations was not considered. In this paper, therefore, we reexamine the nonlinear dynamics of light-like tachyon condensation using a combination of numerical and analytical techniques. We find that for the p-adic string the monotonic behaviour obtained previously relied on a special choice of initial conditions near the unstable maximum. For generic initial conditions the wild oscillations come back to haunt us. Interestingly, we find an ``island of stability'' in initial condition space that leads to sensible evolution at late times. For the string field theory case, on the other hand, we find that the evolution is completely stable for generic choices of initial data. This provides an explicit example of a string theoretic system that admits infinitely many initial data but is nevertheless nonperturbatively stable. Qualitatively similar dynamics are obtained in nonlocal cosmologies where the Hubble damping plays a role very analogous to the dilaton gradient.

Black hole entropy, marginal stability and mirror symmetry

We consider the superconformal quantum mechanics associated to BPS black holes in type IIB Calabi-Yau compactifications. This quantum mechanics describes the dynamics of D-branes in the near-horizon attractor geometry of the black hole. In many cases, the black hole entropy can be found by counting the number of chiral primaries in this quantum mechanics. Both the attractor mechanism and notions of marginal stability play important roles in generating the large number of microstates required to explain this entropy. We compute the microscopic entropy explicitly in a few different cases, where the theory reduces to quantum mechanics on the moduli space of special Lagrangians. Under certain assumptions, the problem may be solved by implementing mirror symmetry as three T-dualities: this is essentially the mirror of a calculation by Gaiotto, Strominger and Yin. In some simple cases, the calculation may be done in greater generality without resorting to conjectures about mirror symmetry. For example, the K3 × T2 case may be studied precisely using the Fourier-Mukai transform.

Generalized Gross-Neveu models and chiral symmetry breaking from string theory

We consider intersecting D-brane models which have two dimensional chiral fermions localized at the intersections. At weak coupling, the interactions of these fermions are described by generalized Gross-Neveu models. At strong coupling, these configurations are described by the dynamics of probe D-branes in a curved background spacetime. We study patterns of dynamical chiral symmetry breaking in these models at weak and strong coupling, and also discuss relationships between these two descriptions.

Delocalization from anomaly inflow and intersecting brane dynamics

We study intersecting D-brane models, that describe at low energies a two dimensional chiral fermion theory localized at the intersection. The fermions are coupled to gauge fields in the bulk. The resulting low energy theory is equivalent to the Gross-Neveu model with dynamical chiral symmetry breaking. No Nambu-Goldstone boson associated with spontaneously broken symmetries appears in two dimensional field theories. In the present work we discuss solvable models with the same basic dynamics of the dual Gross-Neveu model. The disappearance of the Nambu-Goldstone boson is obtained from D-brane dynamics. The mechanism relies on the non-trivial dynamics of a gauge field due to anomaly inflow.

STRING THEORY, QUANTUM MECHANICS AND NONCOMMUTATIVE GEOMETRY: A NEW PERSPECTIVE ON THE GRAVITATIONAL DYNAMICS OF D0-BRANES

We do not know the symmetries underlying string theory. Furthermore, there must exist an inherently quantum, and space–time independent, formulation of this theory. Independent of string theory, there should exist a description of quantum mechanics which does not refer to a classical space–time manifold. We propose such a formulation of quantum mechanics, based on noncommutative geometry. This description reduces to standard quantum mechanics, whenever an external classical space–time is available. However, near the Planck energy scale, self-gravity effects modify the Schrödinger equation to the non-linear Doebner–Goldin equation. Remarkably, this non-linear equation also arises in the quantum dynamics of D0-branes. This suggests that the noncommutative quantum dynamics proposed here is actually the quantum gravitational dynamics of D0-branes, and that automorphism invariance is a symmetry of string theory.

Aspects of D-brane dynamics in supergravity backgrounds with fluxes, kappa-symmetry and equations of motion. Part IIB

We derive and carry out a detailed analysis of the equations of motion of the type IIB D-branes in generic supergravity backgrounds with fluxes making account of the worldvolume Born–Infeld gauge field and putting a special emphasis on the structure of the Dirac equation for D p-brane fermionic modes. We present an explicit form of the worldvolume field equations for each of the D p-branes ( p = 1 , 3 , 5 , 7 , 9 ) in the cases in which the Neveu–Schwarz flux and the Ramond–Ramond p-form flux along the D p-brane worldvolume are zero and the supergravity backgrounds do not necessarily induce the worldvolume Born–Infeld flux. We then give several examples of D3-, D5- and D7-brane configurations in which the worldvolume Born–Infeld flux is intrinsically non-zero and therefore must be taken into account in studying problems where such branes are involved. The examples include D3- and D5-brane instantons carrying (self-dual) worldvolume gauge fields in warped compactification backgrounds.

Unitarity meets channel-duality for rolling/decaying D-branes

Investigations for decay of unstable D-brane and rolling of accelerated D-brane dynamics have revealed that various proposed prescriptions give different result for spectral amplitudes and observables. Here, we study them with particular attention to unitarity and open-closed channel duality. From "ab initio" derivation in the open string channel, both in Euclidean and Lorentzian worldsheet approaches, we find heretofore overlooked contribution to the spectral amplitudes and obervables. The contribution is fortuitously absent for decay of unstable D-brane, but is present for rolling of accelerated D-brane. We finally show that the contribution is imperative for ensuring unitarity and optical theorem at each order in string loop expansion.

INTERSECTING D-BRANE STATES DERIVED FROM THE KP THEORY

A general scheme to find string boundary states is developed within the framework of the theory of KP hierarchy. The method is applied to calculate correlation function of intersecting D-branes and rederived from the results of our previous works as special examples. A matrix generalization of this scheme provides a method to study dynamics of coincident multi D-branes.

Anti-de Sitter D-brane dynamics

We study the anti-de Sitter D-brane dynamics in Hamiltonian formulation. By exploiting the existence of certain conserved charges, we solve the equation of motion for a D1-brane in the AdS3 background and find the space-time dependent solutions. We further study the dynamics by mapping the problem to that of the open string tachyon, and examine the time dependent solutions in some detail.

D-branes and SQCD in non-critical superstring theory

Using exact boundary conformal field theory methods we analyze the D-brane physics of a specific four-dimensional non-critical superstring theory which involves the N=2 SL(2)/U(1) Kazama-Suzuki model at level 1. Via the holographic duality of hep-th/9907178 our results are relevant for D-brane dynamics in the background of NS5-branes and D-brane dynamics near a conifold singularity. We pay special attention to a configuration of D3- and D5-branes that realizes N=1 supersymmetric QCD and discuss the massless spectrum and classical moduli of this setup in detail. We also comment briefly on the implications of this construction for the recently proposed generalization of the AdS/CFT correspondence by Klebanov and Maldacena within the setting of non-critical superstrings.

On reductions of noncommutative anti-self-dual Yang–Mills equations

We show that various noncommutative integrable equations can be derived from noncommutative anti-self-dual Yang–Mills equations in the split signature, which include noncommutative versions of Korteweg–de Vries, nonlinear Schrödinger, N-wave, Davey–Stewartson and Kadomtsev–Petviashvili equations. U(1) part of gauge groups for the original Yang–Mills equations play crucial roles in noncommutative extension of Mason–Sparling's celebrated discussion. The present results would be strong evidences for noncommutative Ward's conjecture and imply that these noncommutative integrable equations could have the corresponding physical pictures such as reduced configurations of D0–D4 brane systems in open N=2 string theories. Possible applications to the D-brane dynamics are also discussed.

D-brane dynamics near compactified NS5-branes

We examine the dynamics of a $Dp$-brane in the background of $k$ coincident, parallel $NS$5-branes which have had one of their common transverse directions compactified. We find that for small energy, bound orbits can exist at sufficiently large distances where there will be no stringy effects. The orbits are dependent upon the energy density, angular momentum and electric field. The analysis breaks down at radial distances comparable with the compactification radius and we must resort to using a modified form of the harmonic function in this region.

Dirac actions for D-branes on backgrounds with fluxes

The understanding of the fermionic sector of the world-volume D-brane dynamics on a general background with fluxes is crucial in several branches of string theory like, for example, the study of nonperturbative effects or the construction of realistic models living on D-branes. In this paper, we derive a new simple Dirac-like form for the bilinear fermionic action for any Dp-brane in any supergravity background, which generalizes the usual Dirac action valid in the absence of fluxes. A non-zero world-volume field strength deforms the usual Dirac operator in the action to a generalized non-canonical one. We show how the canonical form can be re-established by a redefinition of the world-volume geometry.

D-brane dynamics in RR deformation of NS5-branes background and tachyon cosmology

We study D-brane dynamics in the gravity dual background of ODp theories using the effective action on the worldvolume of the brane. We explore the similarities of the system with the rolling tachyon, including the exponential decrease of pressure at late times. We also consider the case where the worldvolume theory on a D 3-brane is coupled to gravity and construct a cosmological model. By considering the time reversal symmetric solutions, we find that we can have both closed and open universes depending on the initial value of the radial mode on the brane. We compare the models with tachyon driven cosmologies and find limits where slow roll inflation is realized.

Kappa-symmetric Derivative Corrections to D-brane Dynamics

We show how the superembedding formalism can be applied to construct manifestly kappa-symmetric higher derivative corrections for the D9-brane. We also show that all correction terms appear at even powers of the fundamental length scale $l$. We explicitly construct the first potential correction, which corresponds to the kappa-symmetric version of the $\partial^4 F^4$, which one finds from the four-point amplitude of the open superstring.