Bootstrapping QCD: the Lake, the Peninsula and the Kink

Understand

We consider the S-matrix bootstrap of four dimensional scattering amplitudes with $O(3)$ symmetry and no bound-states.

• We explore the allowed space of scattering lengths which parametrize the interaction strength at threshold of the various scattering channels.
• Next we consider an application of this formalism to pion physics.
• A signature of pions is that they are derivatively coupled leading to (chiral) zeros in their scattering amplitudes.