The Low Energy π π Amplitude To One and Two Loops

  title={The Low Energy π π Amplitude To One and Two Loops},
  author={Marc Knecht and Bachir Moussallam and Jan Stern},
The low-energy ππ amplitude is computed explicitly to two-loop accuracy in the chiral expansion. It depends only on six independent (combinations of) low-energy constants which are not fixed by chiral symmetry. Four of these constants are determined via sum rules which are evaluated using ππ scattering data at higher energies. Dependence of the low-energy phase shifts and of the threshold parameters on the remaining two constants (called α and β) are discussed and compared to the existing data… CONTINUE READING