D-brane Boundary States Research Articles

Topological superconductors on superstring worldsheets

We point out that different choices of Gliozzi-Scherk-Olive (GSO) projections in superstring theory can be conveniently understood by the inclusion of fermionic invertible phases, or equivalently topological superconductors, on the worldsheet. This allows us to find that the unoriented Type 00 string theory with \Omega^2=(-1)^{f}Ω2=(−1)f admits different GSO projections parameterized by nn mod 8, depending on the number of Kitaev chains on the worldsheet. The presence of nn boundary Majorana fermions then leads to the classification of D-branes by KO^n(X)\oplus KO^{-n}(X)KOn(X)⊕KO−n(X) in these theories, which we also confirm by the study of the D-brane boundary states. Finally, we show that there is no essentially new GSO projection for the Type II worldsheet theory by studying the relevant bordism group, which classifies corresponding invertible phases. In two appendixes the relevant bordism group is computed in two ways.

No pair production of open strings in a plane-wave background

We consider whether an external electric field may cause the pair production of open strings in a type IIA plane-wave background. The boundary states of D-branes with condensates are constructed in the Green-Schwarz formulation of superstring theory with the light-cone gauge. The cylinder diagrams are computed with massive theta functions. Although the value of the electric field is bounded by the upper value, there is no pole in the amplitudes and it indicates that no pair production occurs in the plane-wave background. This result would be universal for a class of plane-wave backgrounds.

Semiclassical bosonic D-brane boundary states in curved spacetime

Abstract In this paper we discuss the existence of quantum D-brane states in the strong gravitational field and in the presence of a constant Kalb-Ramond field. A semiclassical string quantization method in which the spacetime metric g AB and the constant antisymmetric Kalb-Ramond field b AB are treated exactly is employed. In this framework, the semiclassical D-branes are defined at the first order perturbation around the trajectory of the center-of-mass of a string. The set of equations the semiclassical D-branes must satisfy in a general strong gravitational field are given. These equations are solved in the AdS background where it is shown that a D-brane coherent state exists if the operators that project the string fields onto the corresponding Neumann and Dirichlet directions satisfy a set of algebraic constraints. A second set of equations that should be satisfied by the projectors in order that the semiclassical state be compatible with the global structure of the D-brane are derived in the particle limit of a string in the torsionless AdS background.

One-loop masses of open-string scalar fields in string theory

In phenomenological models with D-branes, there are in general open-string massless scalar fields, in addition to closed-string massless moduli fields corresponding to the compactification. It is interesting to focus on the fate of such scalar fields in models with broken supersymmetry, because no symmetry forbids their masses. The one-loop effect may give non-zero masses to them, and in some cases mass squared may become negative, which means the radiative gauge symmetry breaking. In this article we investigate and propose a simple method for calculating the one-loop corrections using the boundary state formalism. There are two categories of massless open-string scalar fields. One consists the gauge potential fields corresponding to compactified directions, which can be understood as scalar fields in uncompactified space-time (related with Wilson line degrees of freedom). The other consists "gauge potential fields" corresponding to transverse directions of D-brane, which emerge as scalar fields in D-brane world-volume (related with brane moduli fields). The D-brane boundary states with constant backgrounds of these scalar fields are constructed, and one-loop scalar masses are calculated in the closed string picture. Explicit calculations are given in the following four concrete models: one D25-brane with a circle compactification in bosonic string theory, one D9-brane with a circle compactification in superstring theory, D3-branes at a supersymmetric C^3/Z_3 orbifold singularity, and a model of brane supersymmetry breaking with D3-branes and anti-D7-branes at a supersymmetric C^3/Z_3 orbifold singularity. We show that the sign of the mass squared has a strong correlation with the sign of the related open-string one-loop vacuum amplitude.

D-branes in non-critical superstrings and minimal super-Yang–Mills in various dimensions

We construct and analyze D-branes in superstring theories in even dimensions less than ten. The backgrounds under study are supersymmetric R d − 1 , 1 × S L ( 2 , R ) k / U ( 1 ) where the level of the supercoset is tuned such as to provide bona fide string theory backgrounds. We provide exact boundary states for D-branes that are localized at the tip of the cigar SL ( 2 , R ) / U ( 1 ) supercoset conformal field theory. We analyze the spectra of open strings on these D-branes and show explicitly that they are consistent with supersymmetry in d = 2 , 4 and 6. The low energy theory on the world-volume of the D-brane in each case is pure Yang–Mills theory with minimal supersymmetry. In the case with four macroscopic flat directions d = 4 , we realize an N = 1 super-Yang–Mills theory, and we interpret the backreaction for the dilaton as the running of the gauge coupling, and study the relation between R-symmetry breaking in the gauge theory and the backreaction on the RR axion.

DDF construction and D-brane boundary states in pure spinor formalism

Open string boundary conditions for non-BPS D-branes in type II string theories discussed in hep-th/0505157 give rise to two sectors with integer (R sector) and half-integer (NS sector) modes for the combined fermionic matter and bosonic ghost variables in pure spinor formalism. Exploiting the manifest supersymmetry of the formalism we explicitly construct the DDF (Del Giudice, Di Vecchia, Fubini) states in both the sectors which are in one-to-one correspondence with the states in light-cone Green-Schwarz formalism. We also give a proof of validity of this construction. A similar construction in the closed string sector enables us to define a physical Hilbert space in pure spinor formalism which is used to project the covariant boundary states of both the BPS and non-BPS instantonic D-branes. These projected boundary states take exactly the same form as those found in light-cone Green-Schwarz formalism and are suitable for computing the cylinder diagram with manifest open-closed duality.

D-branes and closed string field theory

We construct BRST invariant solitonic states in the OSp invariant string field theory for closed bosonic strings. Our construction is a generalization of the one given in the noncritical case. These states are made by using the boundary states for D-branes, and can be regarded as states in which D-branes or ghost D-branes are excited. We calculate the vacuum amplitude in the presence of solitons perturbatively and show that the cylinder amplitude for the D-brane is reproduced. The results imply that these are states with even number of D-branes or ghost D-branes.

On D-brane boundary state analysis in pure spinor formalism

We explore a particular approach to study D-brane boundary states in Berkovits' pure spinor formalism of superstring theories. In this approach one constructs the boundary states in the relevant conformal field theory by relaxing the pure spinor constraints. This enables us to write down the open string boundary conditions for non-BPS D-branes in type II string theories, generalizing our previous work in light-cone Green-Schwarz formalism. As a first step to explore how to apply these boundary states for physical computations we prescribe rules for computing disk one point functions for the supergravity modes. We also comment on the force computation between two D-branes and point out that it is hard to make the world-sheet open-closed duality manifest in this computation.

D-brane boundary states in the pure spinor superstring

We study the construction of D-brane boundary states in the pure spinor formalism for the quantisation of the superstring. This is achieved both via a direct analysis of the definition of D-brane boundary states in the pure spinor conformal field theory, as well as via comparison between standard RNS and pure spinor descriptions of the superstring. Regarding the map between RNS and pure spinor formulations of the superstring, we shed new light on the tree level zero mode saturation rule. Within the pure spinor formalism we propose an explicit expression for the D-brane boundary state in a flat spacetime background. While the non-zero mode sector mostly follows from a simple understanding of the pure spinor conformal field theory, the zero mode sector requires a deeper analysis which is one of the main points in this work. With the construction of the boundary states at hand, we give a prescription for calculating scattering amplitudes in the presence of a D-brane. Finally, we also briefly discuss the coupling to the world-volume gauge field and show that the D-brane low-energy effective action is correctly reproduced.

D-branes in lorentzian AdS3

We study the exact construction of D-branes in Lorentzian AdS(3). We start by defining a family of conformal field theories that gives a natural Euclidean version of the SL(2,R) CFT and does not correspond to H(3)+, the analytic continuation of AdS(3). We argue that one can recuperate the exact CFT results of Lorentzian AdS(3), upon an analytic continuation in the moduli space of these conformal field theories. Then we construct exact boundary states for various symmetric and symmetry-breaking D-branes in AdS(3).

Boundary states for D-branes with traveling waves

We construct boundary states for D-branes which carry traveling waves in the covariant formalism. We compute their vacuum amplitudes to investigate their interactions. In non-compact space, the vacuum amplitudes become trivial as is common in plane wave geometries. However, we found that if they are compactified in the traveling direction, then the amplitudes are affected by non-trivial time dependent effects. The interaction between D-branes with waves traveling in the opposite directions (`pulse-antipulse scattering') are also computed. Furthermore, we apply these ideas to open string tachyon condensation with traveling waves.

Boundary states for D-branes with traveling waves

Boundary states for D-branes with traveling waves

Coupling of rolling tachyon to closed strings

We study the late time behavior of the boundary state representing the rolling tachyon constructed by Sen. It is found that the coupling of the rolling tachyon to massive modes of the closed string grows exponentially as the system evolves. We argue that the description of rolling tachyon by a boundary state is valid during the finite time determined by string coupling, and that energy could be dissipated to the bulk beyond this time. We also comment on the relation between the rolling tachyon boundary state and the spacelike D-brane boundary state.

Boundary States of D-Branes in AdS3 Based on Discrete Series

We study D-branes in the Lorentzian AdS_3 background from the viewpoint of boundary states, emphasizing the role of open-closed duality in string theory. Employing the world sheet with Lorentzian signature, we construct the Cardy states with the discrete series. We show that they are compatible with (1) unitarity and normalizability, and (2) the spectral flow symmetry, in the open string spectrum. We also discuss their brane interpretation. We further show that in the case of superstrings on AdS_3 x S^3 x T^4, our Cardy states yield an infinite number of physical BPS states in the open string channel, on which the spectral flows act consistently.

New system of glioma removal using intraoperative MRI combined with functional mapping

States obtained by projecting boundary states, associated with D-branes, to fixed mass level and momentum generically define non-trivial cohomology classes. For on-shell states the cohomology is the standard one, but when the states are off shell the relevant cohomology is defined using a BRST operator with ghost zero-modes removed. The zero-momentum cohomology falls naturally into multiplets of SO(D − 1, 1). At the massless level, a simple set of D-brane configurations generates the full set of zero-momentum states of standard ghost number, including the discrete states. We give a general construction of off-shell cohomology classes, which exhibits a non-trivial interaction between left- and right-movers that is not seen in on-shell cohomology. This includes, at higher mass levels, states obtained from typical D-brane boundary states as well as states with a more intricate ghost dependence.

Non-BPS branes in a type I orbifold

We analyse the spectrum of non-BPS branes in the type I theory on the orbifold $T^4/{\cal I}_4$. We present a detailed analysis of the action of the worldsheet parity $\Omega$ on the different D-brane boundary state sectors of type IIB on $T^4/{\cal I}_4$, using the covariant formulation. Using these results we derive the spectrum of branes in the type I orbifold. We find $\Z_2$- and $\Z$- charged non-BPS branes. A study of the stability of these branes in the type I orbifold is also presented. We find that the type I non-BPS D-particle and D-instanton remain stable in the orbifold. The D-particle carries no charge whereas the non-BPS D-instanton can carry twisted R-R charge.

Unstable non-BPS D-branes of type-II string theories in light-cone Green–Schwarz formalism

The problem of describing the boundary states of unstable non-BPS D-branes of type-II string theories in light-cone Green–Schwarz (GS) formalism is addressed. Regarding the type II theories in light-cone gauge as different realizations of the SO ̂ (8) k=1 Kac–Moody algebra, the non-BPS D-brane boundary states of these theories are given in terms of the relevant Ishibashi states constructed in this current algebra. Using the expressions for the current modes in terms of the GS variables it is straightforward to reexpress the boundary states in the GS formalism. The problem that remains is the lack of manifest SO (8) covariance in these expressions. We also derive the various known expressions for the BPS and non-BPS D-brane boundary states by starting with the current algebra Ishibashi states.

Orbifold boundary states from Cardy's condition

Boundary states for D-branes at orbifold fixed points are constructed in close analogy with Cardy's derivation of consistent boundary states in RCFT. Comments are made on the interpretation of the various coefficients in the explicit expressions, and the relation between fractional branes and wrapped branes is investigated for $\mathbb{C}^2/\Gamma$ orbifolds. The boundary states are generalised to theories with discrete torsion and a new check is performed on the relation between discrete torsion phases and projective representations.

D0-branes in Gepner models and N = 2 black holes

In this paper D-brane boundary states constructed in Gepner models are used to analyze some aspects of the dynamics of DO-branes in Calabi-Yau compactifications of type II theories to four dimensions. It is shown that the boundary states correspond to BPS objects carrying dyonic charges. By analyzing the couplings to closed string fields a correspondence between the DO-branes and extremal charged black holes in N = 2 supergravity is found.

D-branes in Kazama-Suzuki models

We investigate boundary states of D-branes wrapped around supersymmetric cycles in Kazama-Suzuki models. We show that the geometry of the D-branes corresponds to a generalisation of calibrated geometry. We comment on the link with the geometry of the coset space and discuss how T-duality maps between these boundary states.