3d N=2 mirror symmetry, pq-webs and monopole superpotentials

D3 branes stretching between webs of (p,q) 5branes provide an interesting class of 3d N = 2 theories. For generic pq-webs however the low energy field theory is not known. We use 3d mirror symmetry and Type IIB S-duality to construct Abelian gauge theories corresponding to D3 branes ending on both sides of a pq-web made of many coincident N S5's intersecting one D5. These theories contain chiral monopole operators in the superpotential and enjoy a non trivial pattern of global symmetry enhancements. In the special case of the pq-web with one D5 and one N S5, the 3d low energy SCFT admits three dual formulations. This triality can be applied locally inside bigger quiver gauge theories. We prove our statements using partial mirror symmetry A la Kapustin-Strassler, showing the equality of the S-b(3) partition functions and studying the quantum chiral rings.