6d Conformal Matter
Figure 1. UP: N M5-branes at an orbifold singularity (SCFT point). DOWN: the Coulomb/tensor branch deformation where the N M5-branes are separated along the singularity locus and associated conformal matter which are symbolically represented by wavy lines between adjacent gauge factors.
Prof. Cumrun Vafa, with colleagues from Harvard, University of North Carolina, and Università di Milano Bicocca, Milan, submitted a paper to arXiv: M. Del Zotto, J.J. Heckman, A. Tomasiello, and C. Vafa, "6d Conformal matter," arXiv:1407.6359v3, later published in JHEP (DOI: 10.1007/JHEP02(2015)054).
A single M5-brane probing G, an ADE-type singularity, leads to a system which has G × G global symmetry and can be viewed as "bifundamental" (G, G) matter. For the A N series, this leads to the usual notion of bifundamental matter. For the other cases it corresponds to a strongly interacting (1, 0) superconformal system in six dimensions. Similarly, an ADE singularity intersecting the Hořava-Witten wall leads to a superconformal matter system with E 8 × G global symmetry. In this paper, the authors elucidate the Coulomb/tensor branch of (G, G′) conformal matter using the F-theory realization of these theories. This leads to the notion of fractionalization of an M5-brane on an ADE singularity as well as fractionalization of the intersection point of the ADE singularity with the Hořava-Witten wall. Partial Higgsing of these theories leads to new 6d SCFTs in the infrared, also characterized. This generalizes the class of (1, 0) theories which can be perturbatively realized by suspended branes in IIA string theory. By reducing on a circle, the researchers arrive at novel duals for 5d affine quiver theories. Introducing many M5-branes leads to large N gravity duals.