A Note on New Sources of Gaugino Masses

In IIB orientifold models, the singlet twisted moduli appear in the tree-level gauge kinetic function. They might be responsible for generating gaugino masses if they acquire non-vanishing F-terms. We discuss some aspects of this new possibility, such as the size of gaugino masses and their non-universalities. A possible brane setting is presented to illustrate the usefulness of these new sources.Comment: 7 pages, late

(Pseudo)goldstinos, SUSY fluids, Dirac gravitino and gauginos

We review the emergence and fate of goldstinos in different frameworks. First, we consider a super-Higgs mechanism when supersymmetry breaking is induced by neither an F-term nor a D-term but related to a more general stress energy-momentum tensor. This allows us to build a novel Lagrangian that describes the propagation of a spin-3/2 state in a fluid. Then we briefly review the ubiquitous pseudo-goldstinos when breaking supersymmetry in an extra dimension. We remind that the fermion (gravitino or gaugino) soft masses can be tuned to be of Dirac-type. Finally, we briefly connect the latter to the study of models with Dirac-type gaugino masses and stress the advantage of having both an F and a D-term sizable contributions for the hierarchies of soft-terms as well as for minimizing R-symmetry breaking.Comment: 21 page

Scales and Cosmological Applications of M Theory

I review recent results in three topics of the M-world: (i) Scales. (ii) New dark matter candidates. (iii) Cosmological solutions from p-branes. The three topics are discussed in the framework of Ho\v{r}ava-Witten compactifications. Part (iii) includes comments on cosmological solutions in M-theory describing nucleation of universes through instanton effects and expansions toward asymptotically flat or anti-de-Sitter spaces.Comment: 19 pages, latex, uses sprocl.st

Disordered Extra Dimensions

A very large extra dimension may contain many localized branes. We discuss the possibility to formulate such models as a spin system where each spin indicates the supersymmetry direction preserved by the corresponding brane. In the evolution of the universe, the extra dimensions might have ended into a vacuum made of patches with different orientation of the spins, responsible for the observed breaking of supersymmetry. We discuss the limit where the separation of these patches is by very thin defects described as localization of gravitino masses.Comment: 15 pages, no figure. Typos corrected. References added. Version accepted for publication

Limits on the Size of Extra Dimensions and the String Scale

We give a brief summary of present bounds on the size of possible extra-dimensions as well as the string scale from collider experiments.Comment: 11 pages, 4 figures, uses lathuile.sty . Talks given by I.A. at La Thuile2001 and by K.B. at Moriond200

Small Instantons and Weak Scale String Theory

We consider heterotic string compactifications to four dimensions when instantons shrink to zero size. If the standard model gauge group originates from the new gauge symmetry associated with the small instantons singularity, then the weakly or strongly coupled heterotic string scales can be taken to be arbitrarily low. The SO(32) and E_8\times E_8 gauge groups can then be very weakly coupled even at the string scale and behave as non-abelian global symmetries. We comment on a possible role of small instantons in supersymmetry breaking.Comment: 9 pages, Late