F-term

In theoretical physics, one often analyzes theories with supersymmetry in which F-terms play an important role. In four dimensions, the minimal N=1 supersymmetry may be written using a superspace. This superspace involves four extra fermionic coordinates ${\displaystyle \theta ^{1},\theta ^{2},{\bar {\theta }}^{1},{\bar {\theta }}^{2}}$, transforming as a two-component spinor and its conjugate.

Every superfield—i.e. a field that depends on all coordinates of the superspace—may be expanded with respect to the new fermionic coordinates. There exists a special kind of superfields, the so-called chiral superfields, that only depend on the variables ${\displaystyle \theta }$ but not their conjugates. The last term in the corresponding expansion, namely ${\displaystyle F\theta ^{1}\theta ^{2}}$, is called the F-term. Applying an infinitesimal supersymmetry transformation to a chiral superfield results in yet another chiral superfield whose F-term, in particular, changes by a total derivative. This is significant because then ${\displaystyle \int {d^{4}x\,F(x)}}$ is invariant under SUSY transformations as long as boundary terms vanish. Thus F-terms may be used in constructing supersymmetric actions.

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