Search

Abstract: We perform a general analysis of the R-parity conserving dimension-five operators that can be present beyond the Minimal Supersymmetric Standard Model. Not all these operators are actually independent. We present a method which employs spurion-dependent field redefinitions that removes this “redundancy” and establishes the minimal, irreducible set of these dimension-five operators. Their potential effects on the MSSM Higgs sector are discussed to show that the tree level bound cannot be easily lifted within the approximations used, and quantum corrections are still needed to satisfy the LEPII bound. An ansatz is provided for the structure of the remaining couplings in the irreducible set of operators, which avoids phenomenological constraints from flavor changing neutral currents. The minimal set of operators brings new couplings in the effective Lagrangian, notably “wrong”-Higgs Yukawa couplings and contact fermion–fermion–scalar–scalar interactions, whose effects are expected to be larger than those generated in the MSSM at loop or even tree level. This has implications in particular for LHC searches for supersymmetry by direct squark production. [Copyright &y& Elsevier]

We review the various mechanisms of supersymmetry breaking and its transmission to the observable sector. We argue that hybrid models where gauge dominates over gravity mediation, but gravity provides the main contributions to the Higgs sector masses and the neutralino mass, are able to combine the advantages and reduce the disadvantages of the two transmission mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: We analyze a class of dual pairs of heterotic and type I models based on freely-acting orbifolds in four dimensions. Using the adiabatic argument, it is possible to calculate non-perturbative contributions to the gauge coupling threshold corrections on the type I side by exploiting perturbative calculations on the heterotic side, without the drawbacks due to twisted moduli. The instanton effects can then be combined with closed-string fluxes to stabilize most of the moduli fields of the internal manifold, and also the dilaton, in a racetrack realization of the type I model. [Copyright &y& Elsevier]

Abstract: The role of higher derivative operators in 4D effective field theories is discussed in both non-supersymmetric and supersymmetric contexts. The approach, formulated in the Minkowski space–time, shows that theories with higher derivative operators do not always have an improved UV behaviour, due to subtleties related to the analytical continuation from the Minkowski to the Euclidean metric. This continuation is further affected at the dynamical level due to a field-dependence of the poles of the Green functions of the particle-like states, for curvatures of the potential of order unity in ghost mass units. The one-loop scalar potential in theory with a single higher derivative term is shown to have infinitely many counterterms, while for a very large mass of the ghost the usual 4D renormalisation is recovered. In the supersymmetric context of the O''Raifeartaigh model of spontaneous supersymmetry breaking with a higher derivative (supersymmetric) operator, it is found that quadratic divergences are present in the one-loop self-energy of the scalar field. They arise with a coefficient proportional to the amount of supersymmetry breaking and suppressed by the scale of the higher derivative operator. This is also true in the Wess–Zumino model with higher derivatives and explicit soft breaking of supersymmetry. In both models, the UV logarithmic behaviour is restored in the decoupling limit of the ghost. [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]

Abstract: Within the context of type I strings, we show the equivalence between BPS D9-branes with internal magnetic fluxes in the three torii and non-BPS D3-branes with inverted internal magnetic fluxes . We then construct new supersymmetric examples of orientifolds with discrete torsion which in the past had only non-supersymmetric solutions and emphasize the role of new twisted tadpole cancellation conditions, arising in the presence of magnetic fields, in order to get a consistent spectrum. In a second and independent part of the paper, we construct a new nine-dimensional type IIB orientifold with Scherk–Schwarz deformation which has the peculiarity of introducing a new type of non-BPS O9-planes and which contains as top branes a Scherk–Schwarz deformation of non-BPS D9-branes. The model contains charged D7- and D3-branes with a soft supersymmetry breaking spectrum. [Copyright &y& Elsevier]

Abstract: Tadpoles accompany, in one form or another, all attempts to realize supersymmetry breaking in String Theory, making the present constructions at best incomplete. Whereas these tadpoles are typically large, a closer look at the problem from a perturbative viewpoint has the potential of illuminating at least some of its qualitative features in String Theory. A possible scheme to this effect was proposed long ago by Fischler and Susskind, but incorporating background redefinitions in string amplitudes in a systematic fashion has long proved very difficult. In the first part of this paper, drawing from field theory examples, we thus begin to explore what one can learn by working perturbatively in a “wrong” vacuum. While unnatural in Field Theory, this procedure presents evident advantages in String Theory, whose definition in curved backgrounds is mostly beyond reach at the present time. At the field theory level, we also identify and characterize some special choices of vacua where tadpole resummations terminate after a few contributions. In the second part we present a notable example where vacuum redefinitions can be dealt with to some extent at the full string level, providing some evidence for a new link between IIB and 0B orientifolds. We finally show that NS–NS tadpoles do not manifest themselves to lowest order in certain classes of string constructions with broken supersymmetry and parallel branes, including brane–antibrane pairs and brane supersymmetry breaking models, that therefore have UV-finite threshold corrections at one loop. [Copyright &y& Elsevier]

The physical motivations and consequences of large extra dimensions are reviewed in light of recent developments, in particular mm-sized extra dimensions, gauge coupling unification and neutrino masses. To cite this article: K.R. Dienes et al., C. R. Physique 4 (2003). [Copyright &y& Elsevier]

Abstract: Theoretical and phenomenological implications of R-parity violation in supersymmetric theories are discussed in the context of particle physics and cosmology. Fundamental aspects include the relation with continuous and discrete symmetries and the various allowed patterns of R-parity breaking. Recent developments on the generation of neutrino masses and mixings within different scenarios of R-parity violation are discussed. The possible contribution of R-parity-violating Yukawa couplings in processes involving virtual supersymmetric particles and the resulting constraints are reviewed. Finally, direct production of supersymmetric particles and their decays in the presence of R-parity-violating couplings is discussed together with a survey of existing constraints from collider experiments. [Copyright &y& Elsevier]