43 research outputs found
String Junctions and Non-Simply Connected Gauge Groups
Relations between the global structure of the gauge group in elliptic
F-theory compactifications, fractional null string junctions, and the
Mordell-Weil lattice of rational sections are discussed. We extend results in
the literature, which pertain primarily to rational elliptic surfaces and
obtain pi^1(G) where G is the semi-simple part of the gauge group. We show how
to obtain the full global structure of the gauge group, including all U(1)
factors. Our methods are not restricted to rational elliptic surfaces. We also
consider elliptic K3's and K3-fibered Calabi-Yau three-folds.Comment: latex, 34 pages, 8 figure
Holography and the Higgs branch of N=2 SYM theories
We present a proposal for the description of the Higgs branch of
four-dimensional N=2 supersymmetric Yang-Mills theories in the context of the
AdS/CFT correspondence. We focus on a finite Sp(N) N=2 theory arising as dual
of a configuration of N D3-branes in the vicinity of four D7-branes and an
orientifold 7-plane in type I' string theory. The field theory contains
hypermultiplets in the second rank anti-symmetric and in the fundamental
representations. The Higgs branch has a dual description in terms of gauge
field configurations with non-zero instanton number on the world-volume of the
D7-branes. In this setting the non-renormalisation of the metric on the Higgs
branch implies constraints on the alpha' corrections to the D7-brane effective
action, including couplings to the curvature and five-form field strength. In
the second part of the paper we discuss non-renormalisation properties of BPS
Wilson lines, which are closely related to the physics of the Higgs branch.
Using a formulation of the four-dimensional N=2 theory in terms of a
three-dimensional N=2 superspace we show that the expectation value of certain
Wilson-line operators with hypermultiplets at the end points is independent of
the length and thus coincides with the expectation value of the local operators
parametrising the Higgs branch.Comment: LaTeX, 29 pages, 1 figure; v2: minor corrections, one reference adde