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Supersymmetric component actions via coset approach

We propose a method to construct the on-shell component actions for the theories with $1/2$ partial breaking of global supersymmetry within the nonlinear realization (coset) approach. In contrast with the standard superfield approach in which unbroken supersymmetry plays the leading role, we have shifted the attention to the spontaneously broken supersymmetry. It turns out that in the theories in which half of supersymmetries is spontaneously broken, all physical fermions are just the fermions of the nonlinear realization. Moreover, the transformation properties of these fermions with respect to the broken supersymmetry are the same as in the famous Volkov-Akulov model. Just this fact completely fixed all possible appearances of the fermions in the component action: they can enter the action through the determinant of the vielbein (to compensate the transformation of the volume form) and the covariant derivatives, only. It is very important that in our parametrization of the coset the rest of physical components, i.e. all bosonic components, transform as ``matter fields'' with respect to the broken supersymmetry. Clearly, in such a situation the component action acquires the form of the Volkov-Akulov action for these ``matter fields''. The complete form of the action can be further fixed by two additional requirements: a) to reproduce the bosonic limit, which is explicitly known in many interesting cases, and b) to have a proper linearized form, which has to be invariant with respect to the linearized unbroken supersymmetry. We supply the general consideration by a detailed example of the component action of $N=1$ supermembrane in $D=4$ constructed within our procedure. In this case we provide the exact proof of the invariance of the constructed component action with respect to both, broken and unbroken supersymmetries.