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Abstract: In the context of supersymmetric models where the gauginos may have both Majorana and Dirac masses we investigate the general constraints from flavour-changing processes on the scalar mass matrices. One finds that the chirality-flip suppression of flavour-changing effects usually invoked in the pure Dirac case holds in the mass insertion approximation but not in the general case, and fails in particular for inverted hierarchy models. We quantify the constraints in several flavour models which correlate fermion and scalar superpartner masses. We also discuss the limit of very large Majorana gaugino masses compared to the chiral adjoint and Dirac masses, where the remaining light eigenstate is the “fake” gaugino, including the consequences of suppressed couplings to quarks beyond flavour constraints. [Copyright &y& Elsevier]

Abstract: We study the most general extension of the MSSM Lagrangian that includes scenarios in which supersymmetry is spontaneously broken at a low scale f. The spurion that parametrizes supersymmetry breaking in the MSSM is promoted to a dynamical superfield involving the goldstino, with (and without) its scalar superpartner, the sgoldstino. The low energy effective Lagrangian is written as an expansion in terms of , where ▪ is the induced supersymmetry breaking scale, and contains, in addition to the usual MSSM Lagrangian with the soft terms, couplings involving the component fields of the goldstino superfield and the MSSM fields. This Lagrangian can provide significant corrections to the usual couplings in the Standard Model and the MSSM. We study how these new corrections affect the Higgs couplings to gauge bosons and fermions, and how LHC bounds can be used in order to constrain f. We also discuss that, from the effective field theory point of view, the couplings of the goldstino interactions are not determined by any symmetry, and their usual simple relation to the soft terms is corrected by higher-dimensional operators. [Copyright &y& Elsevier]

Abstract: We show that in gauge mediation models where heavy messenger masses are provided by the adjoint Higgs field of an underlying theory, a generalized gauge mediation spectrum arises with the characteristic feature of having a neutralino LSP much lighter than in the standard gauge or gravity mediation schemes. This naturally fits in a hybrid scenario where gravity mediation, while subdominant with respect to gauge mediation, provides μ and Bμ parameters of the appropriate size for electroweak symmetry breaking. [Copyright &y& Elsevier]

Abstract: We derive general expressions for soft terms in supergravity where D-terms contribute significantly to the supersymmetry breaking in addition to the standard F-type breaking terms. Such D-terms can strongly influence the scalar mass squared terms, while having limited impact on gaugino masses and the B-terms. We present parameterisations for the soft terms when D-terms dominate over F-terms or become comparable with them. Novel patterns emerge which can be tested phenomenologically. In a mixed anomaly-D mediated scenario, the scalars have masses from D-mediation, whereas gaugino masses are generated by anomaly mediation. As an application of this analysis, we show that while the “split supersymmetry” like mass spectrum with one fine tuned Higgs is not an automatic outcome of these scenarios, explicit models can be constructed where it can be realised. Finally, we show that large D-mediated supersymmetry breaking can be realised in string models based on intersecting D-branes. Examples are presented where the moduli are stabilised in the presence of large D-terms using non-perturbative gaugino condensation like effects. [Copyright &y& Elsevier]

Abstract: We provide a description of the five-dimensional Higgs mechanism in supersymmetric gauge theories compactified on the orbifold by means of the superfield formalism. Goldstone bosons absorbed by vector multiplets can come either from hypermultiplets or from gauge multiplets of opposite parity (Hosotani mechanism). Supersymmetry is broken by the Scherk–Schwarz mechanism. In the presence of massive hypermultiplets and gauge multiplets, with different supersymmetric masses, the radion can be stabilized with positive (de Sitter) vacuum energy. The masses of vector and hypermultiplets can be fine-tuned to have zero (Minkowski) vacuum energy. [Copyright &y& Elsevier]

We study the dynamics of type I strings on Melvin backgrounds, with a single or multiple twisted two-planes. We construct two inequivalent types of orientifold models that correspond to (non-compact) irrational versions of Scherk–Schwarz type breaking of supersymmetry. In the first class of vacua, D-branes and O-planes are no longer localized in space–time but are smeared along the compact Melvin coordinate with a characteristic profile. On the other hand, the second class of orientifolds involves O-planes and D-branes that are both rotated by an angle proportional to the twist. In case of “multiple Melvin spaces”, some amount of supersymmetry is recovered if the planes are twisted appropriately and part of the original O-planes are transmuted into new ones. The corresponding boundary and crosscap states are determined. [Copyright &y& Elsevier]

Abstract: We compute instantonic effects in globally consistent orientifold models with discrete torsion and magnetised D-branes. We consider fractional branes and instantons wrapping the same rigid cycles. We clarify and analyse in detail the low-energy effective action on D-branes in these models. We provide explicit examples where instantons induce linear terms in the charged fields, or non-perturbative mass terms are generated. We also find examples where the gauge theory on fractional branes has conformal symmetry at one-loop, broken by instantonic mass terms at a hierarchically small energy scale. [Copyright &y& Elsevier]