  We point out that naive pentaquark correlations function include
two-hadron-reducible contributions, which are given by convolution of baryon
and meson correlation functions and have nothing to do with pentaquark. We show
that the two-hadron-reducible contributions are large in the operator product
expansion of the correlation functions of three existing works on the
pentaquark. Therefore, it is dangerous to draw a conclusion from the sum rules
using naive pentaquark correlation functions with naive ansatz for the spectral
function under the dispersion integral. Instead, we propose to use the
two-hadron-irreducible correlation function, which is obtained by subtracting
the two-hadron-reducible contribution from the naive correlation function.
Taking one of the works as an example we demonstrate how drastically the
results can change if we remove the two-hadron-reducible part from the naive
correlation function. We obtain the result opposite to the original work for
the parity of the pentaquark.
