Stringent constraints on the scalar K pi form factor from analyticity, unitarity and low-energy theorems

Understand

We investigate the scalar K pi form factor at low energies by the method of unitarity bounds adapted so as to include information on the phase and modulus along the elastic region of the unitarity cut.

• Using at input the values of the form factor at t=0 and the Callan-Treiman point, we obtain stringent constraints on the slope and curvature parameters of the Taylor expansion at the origin.
• Also, we predict a quite narrow range for the higher order ChPT corrections at the second Callan-Treiman point.