We generate meson exchange currents mechanisms for the (γ,${\mathrm{\pi }}^{+}$) reaction in nuclei starting from the γN→ππN amplitude on one nucleon and allowing one of the pions to be produced off shell and be absorbed by a second nucleon. Detailed calculations are presented for the γ ${}_{}{}^3{}_{}{}^{}\mathrm{\pi }_{}^{+3\mathrm{}}{}_{}{}^{}$H reaction, where we show that the cross section at large momentum transfers is dominated by these mechanisms, helping improve the agreement with experimental data. It is also shown that the meson exchange currents produce important effects in the photon asymmetry in the Δ-resonance region. © 1996 The American Physical Society.

• Received 18 June 1996

DOI:https://doi.org/10.1103/PhysRevC.54.3160