String theory provides a consistent microscopic framework for gravity and the other fundamental interactions. However, the string-derived models that we understand best differ from our universe in a key aspect: they are spacetime supersymmetric. In this talk, I will introduce supersymmetry and discuss the role it plays in string theory, highlighting the challenges that arise when supersymmetry is broken—both from formal and phenomenological perspectives.

In a curved spacetime, the definition of particles depends on the observer's frame of reference. Consequently, in non-stationary spacetimes, such as those present in the Early Universe during and after inflation or during the gravitational collapse leading to black hole formation, a substantial production of particles may occur. This talk explores the impact of gravitational particle production (GPP) on scenarios generating the observed matter-antimatter asymmetry, particularly in the context of leptogenesis.