We review physical motivations and possible realizations of string vacua with large internal volume and/or low string scale and discuss the issue of supersymmetry breaking. In particular, we describe the key features of Scherk-Schwarz deformations in type I models and conclude by reviewing the phenomenon of “brane supersymmetry breaking”: the tadpole conditions of some type-I models require that supersymmetry be {\it broken at the string scale} on a collection of branes, while being exact, to lowest order, in the bulk and on other branes.

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  Ignatios Antoniadis (Ecole Polytechnique) / Augusto Sagnotti (Pisa, Scuola Normale Superiore & INFN, Pisa) ©2016