• string theory
• string dualities
• 5D SCFTs
• supersymmetry breaking

In the first four chapters of this Thesis we review general aspects of String Theory. Supersymmetric strings, Dp-branes and orientifold planes are introduced in Chapter 2. We also briefly discuss compactifications on Calabi-Yau spaces in Chapter 3 and string dualities in Chapter 4.
Chapter 5 contains a non-perturbative gauge enhancement mechanism implied by string dualities, which has a Field Theory counterpart: some non-renormalisable 5-dimensional SYM theories flow to SCFTs in the UV.
Whether any of these properties extend to non-SUSY theories is still an open problem, but we have made some steps in this direction. In Chapter 5 we review a recent construction from the Field Theory side and describe our attempts to understand it from a String Theory perspective.
In Chapter 6 we reconsider the problem from String Theory, using the Brane Supersymmetry Breaking (BSB) mechanism. The original BSB static and cosmological solutions are reviewed, and we construct the T-dual solutions to the latter. We find, in particular, a closed formula for the T-dualised string coupling and Ricci scalar of the background spaces.
We then review known solutions for T-dual static constructions with O8 planes and D8-branes. These include regions of infinite coupling and infinite curvature, which we use to explore the enhancements in regimes where SUSY is nearly exact.