The Power of Lorentz Invariance

by Prof. Diptimoy Ghosh (IISER Pune)

Friday 27 Dec 2024, 14:30 → 15:30 Asia/Kolkata

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 Effective Field Theories (or Quantum Field Theories at long distances or low energies) find applications in diverse branches of physics, in particular, particle physics, cosmology, and condensed matter systems. Thus narrowing down the space of consistent Effective Field Theories (EFTs) is an important and useful exercise. 

In this talk, I will discuss how the Lorentz-invariant notion of causality imposes nontrivial constraints on low-energy EFTs. In particular, I'll compare the two different ways to get these constraints: the "IR incarnation" - where one demands that the speed of fluctuations about any non-trivial background is subluminal, and the "UV incarnation" - where one uses dispersion relation for 2→2 scattering in the forward limit. At the end, I will briefly outline the challenges that arise when loop effects are taken into account.