Seiji Terashima

Brane-antibrane action from boundary string field theory

In this paper we give the boundary string field theory description of brane-antibrane systems. From the world-sheet action of brane-antibrane systems we obtain the tachyon potential and discuss the tachyon condensation exactly. We also find the world-volume action including the gauge fields. Moreover we determine RR-couplings exactly for non-BPS branes and brane-antibranes. These couplings are written by superconnections and correspond to K1(M) and K0(M) for the non-BPS branes and brane-antibranes, respectively. We also show that Myers terms appear if we include the transverse scalars in the boundary sigma model action.

A note on superfields and noncommutative geometry

Abstract We consider the supersymmetric field theories on the noncommutative R 4 using the superspace formalism on the commutative space. The terms depending on the parameter of the noncommutativity Θ are regarded as the interactions. In this way we construct the N =1 supersymmetric action for the U ( N ) vector multiplets and chiral multiplets of the fundamental, anti-fundamental and adjoint representations of the gauge group. The action for vector multiplets of the products gauge group and its bi-fundamental matters is also obtained. We discuss the problem of the derivative terms of the auxiliary fields.

D-branes, matrix theory and K-homology

In this paper, we study a new matrix theory based on non-BPS D-instantons in type-IIA string theory and D-instanton--anti D-instanton system in type-IIB string theory, which we call K-matrix theory. The theory correctly incorporates the creation and annihilation processes of D-branes. The configurations of the theory are identified with spectral triples, which are the noncommutative generalization of riemannian geometry a la Connes, and they represent the geometry on the world-volume of higher dimensional D-branes. Remarkably, the configurations of D-branes in the K-matrix theory are naturally classified by a K-theoretical version of homology group, called K-homology. Furthermore, we argue that the K-homology correctly classifies the D-brane configurations from a geometrical point of view. We also construct the boundary states corresponding to the configurations of the K-matrix theory, and explicitly show that they represent the higher dimensional D-branes.

A construction of commutative D-branes from Lower dimensional non-BPS D-branes

We construct an exact soliton, which represents a BPS Dp-brane, in a boundary string field theory action of infinitely many non-BPS D(p−1)-branes. Furthermore, we show that this soliton can be regarded as an exact soliton in the full string field theory. The world-volume theory of the BPS Dp-brane constructed in this way becomes usual gauge theory on commutative p+1, instead of non-commutative plane. We also construct a Dp-brane from non-BPS D(p−n)-branes by the ABS like configuration. We confirm that the Dp-brane has correct RR charges and the tension.

Instantons in the U(1) Born–Infeld theory and noncommutative gauge theory

Abstract We derive a BPS-type bound for maximally rotational symmetric configurations in four-dimensional Born–Infeld action with constant B field background. The supersymmetric configuration saturates this bound and is regarded as an analog of instanton in U (1) gauge theory. Furthermore, we find the explicit solutions of this BPS condition. These solutions have a finite action proportional to the instanton number and represent D( p −4)-branes within a Dp-brane although they have a singularity at the origin. Some relations to the noncommutative U (1) instanton are discussed.

S-duality from OM-theory

Abstract We study the compactification of OM-theory on tori and show a simple heuristic derivation of the S -duals of noncommutative open string theory in diverse dimensions from the OM-theoretical point of view. In particular, we identify the S -duality between noncommutative open string theory and noncommutative Yang–Mills theory in 3+1 dimensions as the exchange of two circles of a torus on which OM-theory is compactified. Also, we briefly discuss T -duality between noncommutative open string theories.

Constraints on effective Lagrangian of D-branes from non-commutative gauge theory

Abstract It was argued that there are two different descriptions of the effective Lagrangian of gauge fields on D-branes by non-commutative gauge theory and by ordinary gauge theory in the presence of a constant B field background. In the case of bosonic string theory, however, it was found in the previous works that the two descriptions are incompatible under the field redefinition which relates the non-commutative gauge field to the ordinary one found by Seiberg and Witten. In this paper we resolve this puzzle to observe the necessity of gauge-invariant but B -dependent correction terms involving metric in the field redefinition which have not been considered before. With the problem resolved, we establish a systematic method under the α′ expansion to derive the constraints on the effective Lagrangian imposed by the compatibility of the two descriptions where the form of the field redefinition is not assumed.

On the supersymmetry of non-BPS D-brane

In this paper we extend the boundary string field theory action for a non-BPS D-brane to the one including the target space fermions and the nonlinear supersymmetry with 32 supercharges up to some order. This is based on the idea that the vacuum with a non-BPS D-brane belongs to the spontaneously broken phase of the supersymmetry. As a result, we find that the action is almost uniquely determined up to the field redefinition ambiguities.

On the equivalence between noncommutative and ordinary gauge theories

Recently Seiberg and Witten have proposed that noncommutative gauge theories realized as effective theories on D-brane are equivalent to some ordinary gauge theories. This proposal has been proved, however, only for the Dirac-Born-Infeld action in the approximation of neglecting all derivative terms. In this paper we explicitly construct general forms of the 2n-derivative terms which satisfy this equivalence under their assumption in the approximation of neglecting (2n+2)-derivative terms. We also prove that the D-brane action computed in the superstring theory is consistent with the equivalence neglecting the fourth and higher order derivative terms.

The non-abelian Born-Infeld action and noncommutative gauge theory

In this paper we explicitly show the equivalence between the non-abelian Born-Infeld action, which was proposed by Tseytlin as an effective action on several D-branes, and its noncommutative counterpart for slowly varying fields. This confirms the equivalence between the two descriptions of the D-branes using an ordinary gauge theory with a constant B field background and a noncommutative gauge theory, claimed by Seiberg and Witten. We also construct the general forms of the 2n-derivative terms for non-abelian gauge fields which are consistent with the equivalence in the approximation of neglecting (2n+2)-derivative terms.