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Matrix models for $β$-ensembles from Nekrasov partition functions

We relate Nekrasov partition functions, with arbitrary values of $ε_1,ε_2$ parameters, to matrix models for $β$-ensembles. We find matrix models encoding the instanton part of Nekrasov partition functions, whose measure, to the leading order in $ε_2$ expansion, is given by the Vandermonde determinant to the power $β=-ε_1/ε_2$. An additional, trigonometric deformation of the measure arises in five-dimensional theories. Matrix model potentials, to the leading order in $ε_2$ expansion, are the same as in the $β=1$ case considered in 0810.4944 [hep-th]. We point out that potentials for massive hypermultiplets include multi-log, Penner-like terms. Inclusion of Chern-Simons terms in five-dimensional theories leads to multi-matrix models. The role of these matrix models in the context of the AGT conjecture is discussed.