A New Perturbative Expansion for Fermionic Functional Integrals

We construct a power series representation of the integrals of form \begin{equation} \text{log} \int dμ_{S}(ψ, \barψ) \hspace{0.05 cm} e^{f(ψ, \barψ, η, \barη)} \nonumber \end{equation} where $ψ, \barψ$ and $η, \barη$ are Grassmann variables on a finite lattice in $d \geqslant 2$. Our expansion has a local structure, is clean and provides an easy alternative to decoupling expansion and Mayer-type cluster expansions in any analysis. As an example, we show exponential decay of 2-point truncated correlation function (uniform in volume) in massive Gross-Neveu model on a unit lattice.

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