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In the holographic model of QCD, theta dependence sharply changes at thepoint of confinement deconfinement phase transition. In large N QCD such achange in theta behavior can be related to the breakdown of the instantonexpansion at some critical temperature T_c. Associating this temperature withconfinement-deconfinement phase transition leads to the description of thelatter in terms of dissociation of instantons into the fractionally chargedinstanton quarks. To elucidate this picture, we introduce the nonvanishingchiral condensate in the deconfining phase and assume a specific lagrangian forthe eta' field in the confining phase. In the resulting picture the hightemperature phase of the theory consists of the dilute gas of instantons, whilethe low temperature phase is described in terms of freely moving fractionalinstanton quarks.

Phase Transitions, theta Behavior and Instantons in QCD and its Holographic Model