Three-form multiplet and supersymmetry breaking

Recently, a nilpotent real scalar superfield $V$ was introduced in arXiv:1702.02423 as a model for the Goldstino. It contains only two independent component fields, the Goldstino and the auxiliary $D$-field. Here we first show that $V$ can equivalently be realised as a constrained three-form superfield. We demonstrate that every irreducible Goldstino superfield (of which the Goldstino is the only independent component field) can be realised as a descendant of $V$ which is invariant under local rescalings $V to {rm e}^tau V$, where $tau$ is an arbitrary real scalar superfield. We next propose a new Goldstino supermultiplet which is described by a nilpotent three-form superfield $cal Y$ that is a variant formulation for the nilpotent chiral superfield, which is often used in off-shell models for spontaneously broken supergravity. It is shown that the action describing the dynamics of $cal Y$ may be obtained from a supersymmetric nonlinear $sigma$-model in the infrared limit. Unlike $V$, the Goldstino superfield $cal Y$ contains two independent auxiliary fields, $F= H+{rm i} G$, of which $H$ is a scalar and $G$ is the field strength of a gauge three-form. When $cal Y$ is coupled to supergravity, both $H$ and $G$ produce positive contributions to the cosmological constant. While the contribution from $H$ is uniquely determined by the parameter of the supersymmetry breaking in the action, the contribution from $G$ is dynamical.