Short-range interactions and narrow resonances in effective field theory
We consider the effective field theory (EFT) treatment of two-body systems with narrow resonances. Within this approach, an wave scattering amplitude can be expanded in powers of a typical momentum scale of a system represents a hard scale of a scattering system, and an energy difference , where is a resonance peak energy. It is shown that at leading order in the double expansion a universal form of a two-body scattering amplitude is a sum of a Breit-Wigner term of order , a smooth background term of order , and an interference term of order. The techniques developed in this paper can be used to investigate the properties of narrow resonances that are produced by short-distance dynamics.
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