Two consistency conditions for partition functions established by Akemann and Damgaard in their studies of the fermionic mass dependence of the QCD partition function at low energy (a la Leutwiller-Smilga-Verbaarschot) are interpreted in terms of integrable hierarchies. Their algebraic relation is shown to be a consequence of Wick's theorem for 2d fermionic correlators (Hirota identities) in the special case of the 2-reductions of the KP hierarchy (that is KdV/mKdV). The consistency condition involving derivatives is an incarnation of the string equation associated with the particular matrix model (the particular kind of the Kac-Schwarz operator). (C) 2001 Elsevier Science B.V. All rights reserved. References: 10
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