Amplitude's positivity vs. Subluminality

by Diptimoy Ghosh (ISER Pune)

Friday 5 May 2023, 14:00 → 15:00 Europe/Rome

Aula Touschek (Marconi Building, Second Floor)

Effective Field Theories (EFTs) find applications in diverse branches of physics, in particular, particle physics, cosmology, and condensed matter systems. Thus narrowing down the space of `consistent' EFTs is an important and useful exercise. In this talk, I will discuss causality and unitarity constraints on dimension 6 and dimension 8 Gluon field strength operators in QCD. In particular, I will compare the two different ways to get these bounds: the "IR avatar" - where one demands that the speed of fluctuations about any non-trivial background should not exceed the speed of light, and the "UV avatar" - where one uses dispersion relation for 2→2 scattering in the forward limit. Finally, I will mention an interesting non-relativistic example where the IR avatar (i.e., subluminality) produces a stronger bound than the UV avatar (i.e., S-matrix positivity).