Chandrasekharan, S; Wiese, U-J, *Partition Functions of Strongly Correlated Electron Systems as
"Fermionants"*
(August, 2011) [1108.2461v1] .
**Abstract:**

*We introduce a new mathematical object, the "fermionant"
${\mathrm{Ferm}}_N(G)$, of type $N$ of an $n \times n$ matrix $G$. It
represents certain $n$-point functions involving $N$ species of free fermions.
When N=1, the fermionant reduces to the determinant. The partition function of
the repulsive Hubbard model, of geometrically frustrated quantum
antiferromagnets, and of Kondo lattice models can be expressed as fermionants
of type N=2, which naturally incorporates infinite on-site repulsion. A
computation of the fermionant in polynomial time would solve many interesting
fermion sign problems.*