Browsing by Author "Lerda, Alberto"

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    Brane world effective actions for D-branes with fluxes
    (2005) Bertolini, Matteo; Billó, Marco; Lerda, Alberto; Morales, Jose F.; Russo, Rodolfo; Physics; Elementary Particle Theory
    We develop systematic string techniques to study brane world effective actions for models with magnetized (or equivalently intersecting) D-branes. In particular, we derive the dependence on all NS-NS moduli of the kinetic terms of the chiral matter in a generic non-supersymmetric brane configurations with non-commuting open string fluxes. Near a N=1 supersymmetric point the effective action is consistent with a Fayet-Iliopoulos supersymmetry breaking and the normalization of the scalar kinetic terms is nothing else than the Kahler metric. We also discuss, from a stringy perspective, D and F term breaking mechanisms, and how, in this generic set up, the Kahler metric enters in the physical Yukawa couplings.
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    Stringy Instantons at Orbifold Singularities
    (2007-05-15T12:32:10Z) Argurio, Riccardo; Bertolini, Matteo; Ferretti, Gabriele; Lerda, Alberto; Petersson, Christoffer; Physics; Elementary Particle Theory
    We study the effects produced by D-brane instantons on the holomorphic quantities of a D-brane gauge theory at an orbifold singularity. These effects are not limited to reproducing the well known contributions of the gauge theory instantons but also generate extra terms in the superpotential or the prepotential. On these brane instantons there are some neutral fermionic zero-modes in addition to the ones expected from broken supertranslations. They are crucial in correctly reproducing effects which are dual to gauge theory instantons, but they may make some other interesting contributions vanish. We analyze how orientifold projections can remove these zero-modes and thus allow for new superpotential terms. These terms contribute to the dynamics of the effective gauge theory, for instance in the stabilization of runaway directions.