Luca Martucci

Supersymmetric D-branes and calibrations on general Script N = 1 backgrounds

We study the conditions to have supersymmetric D-branes on general = 1 backgrounds with Ramond-Ramond fluxes. These conditions can be written in terms of the two pure spinors associated to the SU(3) × SU(3) structure on TM⊕TM, and can be split into two parts each involving a different pure spinor. The first involves the integrable pure spinor and requires the D-brane to wrap a generalised complex submanifold with respect to the generalised complex structure associated to it. The second contains the non-integrable pure spinor and is related to the stability of the brane. The two conditions can be rephrased as a generalised calibration condition for the brane. The results preserve the generalised mirror symmetry relating the type IIA and IIB backgrounds considered, giving further evidence for this duality.

D-branes on general Script N = 1 backgrounds: superpotentials and D-terms

We study the dynamics governing space-time filling D-branes on Type II flux backgrounds preserving four-dimensional = 1 supersymmetry. The four-dimensional superpotentials and D-terms are derived. The analysis is kept on completely general grounds thanks to the use of recently proposed generalized calibrations, which also allow one to show the direct link of the superpotentials and D-terms with BPS domain walls and cosmic strings respectively. In particular, our D-brane setting reproduces the tension of D-term strings found from purely four-dimensional analysis. The holomorphicity of the superpotentials is also studied and a moment map associated to the D-terms is proposed. Among different examples, we discuss an application to the study of D7-branes on SU(3)-structure backgrounds, which reproduces and generalizes some previous results.

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.

Actions and fermionic symmetries for D-branes in bosonic backgrounds

In this article we derive the full interacting effective actions for supersymmetric D-branes in arbitrary bosonic type II supergravity backgrounds. The actions are presented in terms of component fields up to second order in fermions. As one expects, the actions are built from the supercovariant derivative operator and the

Nonperturbative effects on seven-brane Yukawa couplings.

\kappa

Generalized non-supersymmetric flux vacua

-symmetry projector. The results take a compact and elegant form exhibiting

Fermions, T-duality and effective actions for D-branes in bosonic backgrounds

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Magnetized E3-brane instantons in F-theory

-symmetry, as well as supersymmetry in a background with Killing spinors. We give the explicit transformation rules for these symmetries in all cases, including the M2-brane. As an example, we analyze the N=2 super-worldvolume field theory defined by a test D4-brane in the supergravity background produced by a large number of D0-branes. This example displays rigid supersymmetry in a curved spacetime.

On moduli and effective theory of N = 1 warped flux compactifications

We analyze nonperturbative corrections to the superpotential of seven-brane gauge theories on type IIB and F-theory warped Calabi-Yau compactifications. We show, in particular, that such corrections modify the holomorphic Yukawa couplings by an exponentially suppressed contribution, generically solving the Yukawa rank-one problem of certain F-theory local models. We provide explicit expressions for the nonperturbative correction to the seven-brane superpotential, and check that it is related to a noncommutative deformation to the tree-level superpotential via a Seiberg-Witten map.

Review: Dirac's Observables for the Rest-Frame Instant Form of Tetrad Gravity in a Completely Fixed 3-Orthogonal Gauge

We discuss a novel strategy to construct 4D = 0 stable flux vacua of type II string theory, based on the existence of BPS bounds for probe D-branes in some of these backgrounds. In particular, we consider compactifications where D-branes filling the 4D space-time obey the same BPS bound as they would in an = 1 compactification, while other D-branes, like those appearing as domain walls from the 4D perspective, can no longer be BPS. We construct a subfamily of such backgrounds giving rise to 4D = 0 Minkowski no-scale vacua, generalizing the well-known case of type IIB on a warped Calabi-Yau. We provide several explicit examples of these constructions, and compute quantities of phenomenological interest like flux-induced soft terms on D-branes. Our results have a natural, simple description in the language of Generalized Complex Geometry, and in particular in terms of D-brane generalized calibrations. Finally, we extend the integrability theorems for 10D supersymmetric type II backgrounds to the = 0 case and use the results to construct a new class of = 0 AdS4 compactifications.