Special Seminar – Behind & Beyond the Standard Model (Day 5)
Riccardo Rattazzi, EPFL Lusanne
Abstract: This course is essentially divided into three parts. I first introduce the modern Effective Field Theory perspective on Quantum Field Theory. I discuss in particular the role of symmetries and the notion of naturalness, offering a critical analysis of the origin of hierarchical mass scale separations. In the second part I analyze in the light of those concepts the Standard Model, highlighting how its remarkable phenomenological adequacy structurally relies on a seemingly unnatural scale separation. In the third part, I present the two main extensions of the SM, Compositeness and ! Supersymmetry, capable of producing a natural scale separation. I illustrate how these scenarios spoil the structural simplicity at the basis of the phenomenological adequacy of the SM and require somewhat ad hoc model building hypotheses. That creates a paradoxical tension between naturalness and simplicity, which defines in my mind the so-called hierarchy paradox. I will illustrate where past, present and future collider experiments stand in the exploration of this matter. Sections 1. Ideology. The two modern perspectives on QFT: Effective Field Theory and RG-flow 2. Symmetries, Selection rules & Naturalness 3. Behind the Standard Model, or the SM as an EFT 4. Beyond the Standard Model – Supersymmetry – Compositeness – Naturalness vs Simplicity.
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