Related papers: Corrections to D-brane Action and Generalized Boun…
D-brane backgrounds are specified in closed string theories by holes with appropriate mixed Dirichlet and Neumann boundary conditions on the string worldsheet. As presently stated, the prescription defining D-brane backgrounds is such that…
S-duality symmetry of type IIB string theory predicts the existence of a stable non-BPS state on an orbifold five plane of the type IIB theory if the orbifold group is generated by the simultaneous action of (-1)^{F_L} and the reversal of…
We construct the world-volume action for non-BPS D-branes in type II string theories. This action is invariant under all the unbroken supersymmetries in the bulk, but these symmetries are realised as spontaneously broken symmetries in the…
The central theme of this thesis is noncommutativity in string theory. We explore in detail how noncommutative structures can emerge in case of the interacting bosonic string and even in the fermionic sector of superstring theory. We have…
We extend the recently constructed double field theory formulation of the low-energy theory of the closed bosonic string to the heterotic string. The action can be written in terms of a generalized metric that is a covariant tensor under…
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…
A Dp-brane can be regarded as a configuration of infinitely many D(p-2k)-branes in bosonic string. We will show this property of D-branes in the superstring case using the hybrid formalism. It is convenient to study the boundary state for…
The formal extension of the T-duality rules for open strings from Abelian to non-Abelian gauge field background leads in a well known manner to the notion of matrix valued D-brane position. The application of this concept to the non-Abelian…
In this paper we will study tachyon effective action for Dp-brane in bosonic string theory in the linear dilaton background. We obtain the tachyon effective Lagrangian from boundary state coeficient of Dp-brane in the linear dilaton…
In this paper we consider the worldsheet of superstring as a noncommutative space. Some additional terms can be added to the superstring action, such that for ordinary worldsheet they are zero. Expansion of this extended action up to the…
We present a complete study of boundary bound states and related boundary S-matrices for the sine-Gordon model with Dirichlet boundary conditions. Our approach is based partly on the bootstrap procedure, and partly on the explicit solution…
We study open strings in the noncritical $c=1$ bosonic string theory compactified on a circle at self-dual radius. These strings live on D-branes that are extended along the Liouville direction ({\it FZZT} branes). We present explicit…
First we briefly outline the general construction of Dp-brane models with dynamical tensions. We then proceed to a more detailed discussion of a modified string model where the string tension is related to the potential of (an external)…
We study D-branes in the null-brane background. Using the covariant formalism of the worldsheet theory, we construct the boundary states describing D-branes on the null-brane. From the cylinder amplitudes, we find that the D-branes with…
We study non-perturbative effects in supersymmetric U(N) gauge theories in eight dimensions realized by means of D(-1)/D7-brane systems with non-trivial world-volume fluxes turned on. Using an explicit string construction in terms of vertex…
Spacetime non-commutativity appears in string theory. In this paper, the non-commutativity in string theory is reviewed. At first we review that a Dp-brane is equivalent to a configuration of infinitely many D($p-2$)-branes. If we consider…
In string theory, we can geometrically realize a metastable state by wrapping D5-branes and anti D5-branes to a singular manifold. We consider wrapping D3-branes to the internal space in this setup. These D3-branes dissolve into the domain…
A review of various aspects of superstrings in background electromagnetic fields is presented. Topics covered include the Born-Infeld action, spectrum of open strings in background gauge fields, the Schwinger mechanism, finite-temperature…
Aspects of the supersymmetric extension of the Pohlmeyer invariants are studied, and their relation to superstring boundary states for non-abelian gauge fields is discussed. We show that acting with a super-Pohlmeyer invariant with respect…
The study of conformal boundary conditions for two-dimensional conformal field theories (CFTs) has a long history, ranging from the description of impurities in one-dimensional quantum chains to the formulation of D-branes in string theory.…