Correlation functions of the integrable higher-spin XXX and XXZ spin chains through the fusion method

For the integrable higher-spin XXX and XXZ spin chains we present multiple-integral representations for the correlation function of an arbitrary product of Hermitian elementary matrices in the massless ground state. We give a formula expressing it by a single term of multiple integrals. In particular, we explicitly derive the emptiness formation probability (EFP). We assume $2s$-strings for the ground-state solution of the Bethe ansatz equations for the spin-$s$ XXZ chain, and solve the integral equations for the spin-$s$ Gaudin matrix. In terms of the XXZ coupling $Δ$ we define $ζ$ by $Δ=\cos ζ$, and put it in a region $0 \le ζ< π/2s$ of the gapless regime: $-1 < Δ\le 1$ ($0 \le ζ< π$), where $Δ=1$ ($ζ=0$) corresponds to the antiferromagnetic point. We calculate the zero-temperature correlation functions by the algebraic Bethe ansatz, introducing the Hermitian elementary matrices in the massless regime, and taking advantage of the fusion construction of the $R$-matrix of the higher-spin representations of the affine quantum group.

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