Instanton-dyon ensembles with quarks with modified boundary conditions

We modify the quark periodicity condition on the thermal circle by the introduction of some phases - known also as "flavor holonomies" - different quark flavors. These phases provide a valuable tool, to be used for better understanding of deconfinement and chiral restoration phase transitions: by changing them, one can dramatically modify both phase transitions. In the language of instanton constituents - instanton-dyons or monopoles - changing the quark periodicity condition has a very direct explanation: the interplay of flavor and color holonomies can switch topological zero modes between various dyon types. The model we will study in detail, the so-called ZNc-symmetric QCD model with equal number of colors and flavors Nc=Nf=2 and special arrangement of flavor and color holonomies, ensures the "most democratic" setting, in which each quark flavor and each dyon type are in one-to-one correspondence. The usual QCD has the opposite "most exclusive" arrangement: all quarks are antiperiodic and, thus, all zero modes fall on only one - twisted or L - dyon type. As we show by ensemble simulation, deconfinement and chiral restoration phase transitions in these two models are dramatically different. In the usual QCD, both are smooth crossovers: but in the case of the Z2-symmetric model, deconfinement becomes a strong first-order transition, while chiral symmetry remains broken for all dyon densities studied. These results are in good correspondence with those from recent lattice simulations.