Gabriele CASAGRANDE

PhD Student

Research group: String Theory  

Thesis: "Swampland and supersymmetry breaking in strings and brane models"

Advisor: Emilian Dudas

Research

String Theory, Supergravity, Effective field theories

An ambitious program called Swampland propose to identify the constraints on quantum field theories and gauge theories, coming from their coupling to gravity. A quantum field or gauge theory is said to belong to the Swampland if it looks completely consistent from the usual consistency rules viewpoint, but cannot be obtained from a string theory or, more generally, coupled to a quantum theory of gravitation.

Several conjectures were formulated in this respect, with arguments of different degrees of levels of rigor. Among these, we can mention the weak gravity conjecture (postulating that there always exist a particle for which gravity is the weakest force), the de Sitter conjecture (postulating the impossibility to realize a positive cosmological constant), the distance conjecture (the impossibility to realize trans-planckian excursions in field space with an effective theory, question of importance for in ation), etc.

The main goal of the Swampland program is to identify new constraints on the extensions of the Standard Model of fundamental interactions and Cosmology, coming from their coupling to quantum gravity. The majority of string arguments and examples considered in the literature are based on models with extended supersymmetry, which do not allow to define chiral fermions. The main goals of this thesis proposal are:
• the test of some of these conjectures in the case where supersymmetry is minimal infour dimensions, which allows the definition of chiral fermions;
• the identification and study of theories where supersymmetry is completely broken, without introducing instabilities;
• the modifications of the Swampland conjectures in case with no supersymmetry. Formulate new consistency rules in such cases;
• applications of the results obtained to cosmology and high-energy particle physics.