Browsing by Author "Ferretti, Gabriele"

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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.
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    Unscreening the Gaugino Mass with Chiral Messengers
    (2010-07-23T10:33:51Z) Argurio, Riccardo; Bertolini, Matteo; Ferretti, Gabriele; Mariotti, Alberto; Physics; Elementary Particle Theory
    Gaugino screening, the absence of next-to-leading order corrections to gaugino masses, is a generic feature of gauge mediation models of supersymmetry breaking. We show that in a specific class of models, known as semi-direct gauge mediation, it is possible to avoid gaugino screening by allowing for a chiral messenger sector. Messengers then acquire a mass at some scale, for instance by higgsing or by some auxiliary strong coupling dynamics. We implement this idea in a simple model which we work out explicitly.