Standard Model EFTs via On-Shell Methods

Understand

We present the Standard Model Effective Field Theories (SMEFT) from purely on-shell arguments.

• Starting from a few basic assumptions such as Poincar\'e invariance and locality, we classify all the renormalisable and non-renormalisable interactions at the lowest order in the couplings.
• From these building blocks, we review how locality and unitarity enforce Lie algebra structures to appear in the S-matrix elements together with relations among couplings (and hypercharges).
• Furthermore, we give a fully on-shell algorithm to compute any higher-point tree-level amplitude (or form factor) in generic EFTs, bypassing BCFW-like recursion relations which are known to be problematic when non-renormalisable interactions are involved.