Bands and gaps in Nekrasov partition function

We discuss the effective twisted superpotentials of 2d $N=(2,2)$ theories arising upon the reduction of 4d $N=2$ gauge theories on the $\Omega$-deformed cigar-like geometry. We explain field-theoretic origins of the gaps in the spectrum in the corresponding quantum mechanical (QM) systems. We find local 2d descriptions of the physics near these gaps by resumming the non-perturbative part of the twisted superpotential and discuss arising wall-crossing phenomena. The interpretation of the associated phenomena in the classical Liouville theory and in the scattering of two heavy states in ${AdS}_3$ gravity is suggested. Some comments concerning a possible interpretation of the band structure in QM in terms of the Schwinger monopole-pair production in 4d are presented.