  We consider the longitudinal dynamical two-point function of the XXZ quantum
spin chain in the antiferromagnetic massive regime. It has a series
representation based on the form factors of the quantum transfer matrix of the
model. The $n$th summand of the series is a multiple integral accounting for
all $n$-particle $n$-hole excitations of the quantum transfer matrix. In
previous works the expressions for the form factor amplitudes appearing under
the integrals were either again represented as multiple integrals or in terms
of Fredholm determinants. Here we obtain a representation which reduces, in the
zero-temperature limit, essentially to a product of two determinants of finite
matrices whose entries are known special functions. This will facilitate the
further analysis of the correlation function.
