4 research outputs found
A second order algebraic knot concordance group
We define an algebraic group comprising symmetric chain complexes which
captures the first two stages of the Cochran-Orr-Teichner solvable filtration
of the knot concordance group in a single invariant. To achieve this we impose
additional structure on each chain complex which puts extra control on the
fundamental groups, and in particular on the way in which they can change in a
concordance.Comment: 51 pages, 2 figures. This a considerably shortened version of
arXiv:1109.0761, to appear in Algebraic and Geometric Topolog
An introduction to moduli stacks, with a view towards Higgs bundles on algebraic curves
This article is based in part on lecture notes prepared for the summer school
"The Geometry, Topology and Physics of Moduli Spaces of Higgs Bundles" at the
Institute for Mathematical Sciences at the National University of Singapore in
July of 2014. The aim is to provide a brief introduction to algebraic stacks,
and then to give several constructions of the moduli stack of Higgs bundles on
algebraic curves. The first construction is via a "bootstrap" method from the
algebraic stack of vector bundles on an algebraic curve. This construction is
motivated in part by Nitsure's GIT construction of a projective moduli space of
semi-stable Higgs bundles, and we describe the relationship between Nitsure's
moduli space and the algebraic stacks constructed here. The third approach is
via deformation theory, where we directly construct the stack of Higgs bundles
using Artin's criterion.Comment: 145 pages, AMS LaTeX, to appear in the NUS IMS Lecture Note Series on
The Geometry, Topology, and Physics of Moduli Spaces of Higgs Bundle
The Representation and Perception of Roman Imperial Power
Ancient history: to c 500 C