Effective Action For D-branes Research Articles

Closed superstring moduli tree-level two-point scattering amplitudes in Type IIB orientifold on T6/(Z2 × Z2)

We reconsider the two-point string scattering amplitudes of massless Neveu-Schwarz–Neveu-Schwarz states of Type IIB orientifold superstring theory on the disk and projective plane in ten dimensions and analyse its α′ expansion. We also discuss the unoriented Type IIB theory on T6/Z2×Z2 where two-point string scattering amplitudes of the complex Kähler moduli and complex structures of the untwisted sector are computed on the disk and projective plane. New results are obtained together with known ones. Finally, we compare string scattering amplitudes results at α′2-order with the (curvature)2 terms in the low energy effective action of D-branes and Ω-planes in both cases.

Nonlinear [formula omitted] supersymmetry, effective actions and moduli stabilization

Nonlinear supersymmetry is used to compute the general form of the effective D-brane action in type I string theory compactified to four dimensions in the presence of internal magnetic fields. In particular, the scalar potential receives three contributions: (1) a nonlinear part of the D-auxiliary component, associated to the Dirac–Born–Infeld action; (2) a Fayet–Iliopoulos (FI) D-term with a moduli-dependent coefficient; (3) a D-auxiliary independent (but moduli dependent) piece from the D-brane tension. Minimization of this potential leads to three general classes of vacua with moduli stabilization: (i) supersymmetric vacua allowing in general FI terms to be cancelled by non-trivial vacuum expectation values (VEV's) of charged scalar fields; (ii) anti-de Sitter vacua of broken supersymmetry in the presence of a non-critical dilaton potential that can be tuned at arbitrarily weak string coupling; (iii) if the dilaton is fixed in a supersymmetric way by three-form fluxes and in the absence of charged scalar VEV's, one obtains non-supersymmetric vacua with positive vacuum energy.

The effective action of D‐branes in Calabi‐Yau orientifold compactifications

AbstractIn this review article we study type IIB superstring compactifications in the presence of space‐time filling D‐branes while preserving 𝒩=1 supersymmetry in the effective four‐dimensional theory. This amount of unbroken supersymmetry and the requirement to fulfill the consistency conditions imposed by the space‐time filling D‐branes lead to Calabi‐Yau orientifold compactifications. For a generic Calabi‐Yau orientifold theory with space‐time filling D3‐ or D7‐branes we derive the low‐energy spectrum. In a second step we compute the effective 𝒩=1 supergravity action which describes in the low‐energy regime the massless open and closed string modes of the underlying type IIB Calabi‐Yau orientifold string theory. These 𝒩=1 supergravity theories are analyzed and in particular spontaneous supersymmetry breaking induced by non‐trivial background fluxes is studied. For D3‐brane scenarios we compute soft‐supersymmetry breaking terms resulting from bulk background fluxes whereas for D7‐brane systems we investigate the structure of D‐ and F‐terms originating from worldvolume D7‐brane background fluxes. Finally we relate the geometric structure of D7‐brane Calabi‐Yau orientifold compactifications to 𝒩=1 special geometry.

Topological masses from broken supersymmetry

We develop a formalism for computing one-loop gravitational corrections to the effective action of D-branes. In particular, we study bulk to brane mediation of supersymmetry breaking in models where supersymmetry is broken at the tree-level in the closed string sector (bulk) by Scherk–Schwarz boundary conditions, while it is realized on a collection of D-branes in a linear or non-linear way. We compute the gravitational corrections to the fermion masses m 1/2 (gauginos or goldstino) induced from the exchange of closed strings, which are non-vanishing for world-sheets with Euler characteristic −1 (“genus 3/2”) due to a string diagram with one handle and one hole. We show that the corrections have a topological origin and that in general, for a small gravitino mass, the induced mass behaves as m 1/2∝ g 4 m 3/2, with g the gauge coupling. In generic orbifold compactifications however, this leading term vanishes as a consequence of cancellations caused by discrete symmetries, and the remainder is exponentially suppressed by a factor of exp(−1/ α′ m 2 3/2).

Higher order terms in the non-abelian D-brane effective action and magnetic background fields

Recently a proposal for the non-abelian effective D-brane action was given through fourth order in alpha'. As the resulting expressions turned out to be quite involved, some checks of this result are called for. In the present paper we calculate the spectrum in the presence of constant magnetic background fields and compare it to the string theoretical result. Apart from a small typo in the original expression (the overall sign of thefourth order term), we obtain perfect agreement. We discuss potential applications.

Testing the fermionic terms in the non-abelian D-brane effective action through order α′3

Recently the construction of the non-abelian effective D-brane action was performed through order $\alpha'{}^3$ including the terms quadratic in the gauginos. This result can be tested by calculating the spectrum in the presence of constant magnetic background fields and comparing it to the string theoretic predictions. This test was already performed for the purely bosonic terms. In this note we extend the test to the fermionic terms. We obtain perfect agreement.

On non-abelian low energy effective action for D-branes

Connection between the partition function for the 2D sigma model with boundary pertubations and the low energy effective action for massless fields from in the open string theory is discussed. In the non-abelian case with a stack of $N$ D-branes, the terms up to the order of $\alpha'^3$ are found

Effective action for D-branes on SU(2)/U(1) gauged WZW model

Dynamics of D-branes on $SU(2)/U(1)$ gauged WZW model are investigated. We find the effective action for infinite $k$, where $k$ is the level of WZW model. We also consider finite $k$ correction to the effective action which is compatible with Fedosov's deformation quantization of the background.

On α′2 corrections to the D-brane action for non-geodesic world-volume embeddings

In hep-th/9903210 (curvature)$^2$ terms of the effective D-brane action were derived to lowest order in the string coupling. Their results are correct up to ambiguous terms which involve the second fundamental form of the D-brane. We compute five point string amplitudes on the disk. We compare the subleading order in $\alpha'$ of the string amplitudes with the proposed lagrangian of hep-th/9903210 supplemented by the ambiguous terms. The comparison determines the complete form of the gravitational terms in the effective D-brane action to order ${\calO}(\alpha^{' 2})$. Our results are valid for arbitrary ambient geometries and world-volume embeddings.