arXiv:1703.01013v1 [hep-th] 3 Mar 2017 IPMU-17-0032 Anomaly matching on the Higgs branch Hiroyuki Shimizu, Yuji Tachikawa and Gabi Zafrir Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, Chiba 277-8583, Japan We point out that we can almost always determine by the anomaly matching the full anomaly polynomial of a supersymmetric theory in 2d, 4d or 6d if we assume that its Higgs branch is the one-instanton moduli space of some groupG. This method not only provides by far the simplest method to compute the central charges of known theories of this class, e.g. 4dE6,7,8theories of Minahan and Nemeschansky or the 6d E-string theory, but also gives us new pieces of information about unknown theories of this class.
1Introduction Instantons of classical groups can be described in terms of the ADHM construction [1], which can in turn be realized as the Higgs branch of supersymmetric gauge theories [2, 3]. These gauge theories arise as the worldvolume theories on perturbativep-branes probing perturbative(p+ 4)-branes, and the motion into the Higgs branch corresponds to the process wherep-branes get absorbed as instantons of the gauge fields on(p+ 4)-branes. In string/M/F theory, there are also non-perturbative branes that host exceptional gauge groups, and if we probe them by lower-dimensional branes, we get supersymmetric theories whose Higgs branch equals to the instanton moduli spaces of exceptional groups. Among them we can count the 4d theories of Minahan and Nemeschansky [4, 5] forE6,7,8instantons and the 6d E-string theory [6, 7]. The theories obtained this way do not usually have any conventional Lagrangian descriptions, and were therefore rather difficult to study. Even their anomaly polynomials, or equivalently the conformal central charges assuming that they become superconformal in the infrared, needed to be computed first with stringy techniques [8, 9] and then with rather lengthy field theoretical arguments on the Coulomb branch in 4d or on the tensor branch in 6d [10, 11, 12]. In this paper, we point out that the anomaly matching on the Higgs branch almost always allows us to determine the full anomaly polynomial, when the theory is 6dN= (1,0), 4dN= 2, or 2dN= (4,0), and when the Higgs branch is assumed to be the one-instanton moduli space of some groupG. This is because on the generic point of the Higgs branch the theory becomes free and the unbroken symmetry still knows theSU(2)Rsymmetry at the origin. This method provides the simplest way to compute the anomaly polynomials of 4d theories of Minahan and Nemeschansky and the 6d E-string theory. But more importantly, this method gives us new pieces of information about a theory whose Higgs branch is the one-instanton moduli space of the groupG, even when no string/M/F theory construction is known. For example, in [13], the conformal bootstrap method was used to determine the conformal central charges of the 4d theory whose Higgs branch is the one-instanton moduli space ofG2orF4. Our method reproduces the values they obtained, and not only that, we find a strong indication that theF4theory does not exist because of a field theoretical inconsistency. Similarly, we will see that there cannot be any 6dE6,7theory. The rest of the paper is organized as follows. In Section 2, we describe in more detail how the anomaly matching on the Higgs branch works if the Higgs branch is the one-instanton moduli space of some groupG. In Section 3, we summarize the results which we obtained in this paper. Then in Section 4, 5, 6, we study the 6dN= (1,0)theories, the 4dN= 2theories, and the 2d N= (4,0)theories in turn. In Appendix A, we collect the formulas for characteristic classes used throughout in this paper. 1
Gh∨G′R′short comment SU(n)nU(1)F×SU(n−2)(n−2)−n⊕(n−2)+n SO(n)n−2SU(2)F×SO(n−4)2F⊗(n−4) Sp(n)n+ 1Sp(n−1)2n−2 E612SU(6)203-index antisym. E718SO(12)32chiral spinor. E830E756 F49Sp(3)14′3-index antisym. traceless. G24SU(2)F43-index sym. Table 1: The data. ForSU(n),U(1)Fis normalized so thatnsplits as(n−2)−2and2n−2. For SO(n),nis assumed to be≥5. 2Basic idea We consider a theory with 6dN= (1,0)or 4dN= 2or 2dN= (4,0)supersymmetry has a Higgs branch given by the one-instanton moduli spaceMGof a groupG. Geometric data:Let us first recall some basic information onMG, whose detail can be found e.g. in [14] and the references therein. The quaternionic dimension ofMGish∨(G)−1. We note that forG= Sp(n), the one-instanton moduli space is simplyHn/Z2, whereHis the space of quaternions. Furthermore, the moduli space is smooth on a generic point, and the symmetrySU(2)R×G acting onMGis broken toSU(2)D×G′, whereSU(2)X×G′⊂Gis a particular subgroup described in more detail below andSU(2)Dis the diagonal subgroup ofSU(2)RandSU(2)X. The subgroupSU(2)Xis theSU(2)subgroup associated to the highest root ofGandG′is its commutant withinG. The tangent space ofMGat a generic point transforms underSU(2)X×G′ as a neutral hypermultiplet and a charged half-hypermultiplet in a representationR, with the rule g=g′⊕su(2)⊕R.(2.1) HereRis always of the form of the doublet ofSU(2)Xtensored with a representationR′ofG′. The subgroupG′and the representationR′are given in the table 1. Strategy of the matching:Now let us explain how the anomaly matching on the Higgs branch works. At the origin, the theory has the symmetrySU(2)R×GwhereSU(2)Ris (part of) the R-symmetry. 2
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