Effective theories of universal theories

Understand

It is well-known but sometimes overlooked that constraints on the oblique parameters (most notably $S$ and $T$ parameters) are generally speaking only applicable to a special class of new physics scenarios known as universal theories.

• In the effective field theory (EFT) framework, the oblique parameters should not be associated with Wilson coefficients in a particular operator basis, unless restrictions have been imposed on the EFT so that it describes universal theories.
• We work out these restrictions, and present a detailed EFT analysis of universal theories.
• We find that at the dimension-6 level, universal theories are completely characterized by 16 parameters.