Lunch seminar Riccardo Argurio

Title:
Goldstones, or not, in QFT and Holography

Abstract:
Symmetry breaking, both spontaneous and explicit, will be approached using Ward identities as the main tool.

We will first recall how Ward identities encode the spectrum of gapless, or nearly gapless modes (a.k.a. Goldstone bosons), emphasizing when UV or IR data is needed. We then proceed to consider also the holographic perspective on this problem. We will discuss a selection of models, from the training ground of a global U(1) symmetry, to models where Lorentz invariance is absent, such as in presence of a chemical potential or for theories with Lifshitz scaling.

We will also consider the critical dimension below which large quantum fluctuations prevent symmetry breaking, in each of these cases. If time allows, we will also discuss the breaking of translations.