We solve the Lippmann-Schwinger equation (LSE) with a kernel that includes a regular finite-range potential and additional contact terms with derivatives. We employ distorted wave theory and dimensional regularization, as proposed in Nieves [Phys. Lett. B 568, 109 (2003)]. We analyze the spin singlet nucleon-nucleon $S$-wave as case of study, with the regular one-pion exchange (OPE) potential in this partial wave and up to $\mathcal{O}(Q^6)$ (six derivatives) contact interactions. We discuss in detail the renormalization of the LSE and show that the scattering amplitude solution of the LSE fulfills exact elastic unitarity and inherits the left-hand cut of the long-distance OPE amplitude. Furthermore, we proof that the LSE amplitude coincides with that obtained from the exact $N/D$ calculation, with the appropriate number and typology of subtractions to reproduce the effective range parameters taken as input to renormalize the LSE amplitude. The generalization to a higher number of derivatives is straightforward.

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• Bethe-Salpeter equation
• Effective field theory
• Scattering amplitudes