Low-scale SUSY breaking and the (s)goldstino physics

For a 4D N=1N=1 supersymmetric model with a low SUSY breaking scale (f  ) and general Kahler potential K(Φi,Φj†) and superpotential W(Φi)W(Φi) we study, in an effective theory approach, the relation of the goldstino superfield to the (Ferrara–Zumino) superconformal symmetry breaking chiral superfield X. In the presence of more sources of supersymmetry breaking, we verify the conjecture that the goldstino superfield is the (infrared) limit of X   for zero-momentum and Λ→∞Λ→∞ (Λ   is the effective cut-off scale). We then study the constraint X2=0X2=0, which in the one-field case is known to decouple a massive sgoldstino and thus provide an effective superfield description of the Akulov–Volkov action for the goldstino. In the presence of additional fields that contribute to SUSY breaking we identify conditions for which X2=0X2=0 remains valid, in the effective theory below a large but finite sgoldstino mass. The conditions ensure that the effective expansion (in 1/Λ1/Λ) of the initial Lagrangian is not in conflict with the decoupling limit of the sgoldstino (1/msgoldstino∼Λ/f1/msgoldstino∼Λ/f, f<Λ2f<Λ2).