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Search: MSC category 14D20 ( Algebraic moduli problems, moduli of vector bundles {For analytic moduli problems, see 32G13} )

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1. CJM 2011 (vol 63 pp. 755)

Chu, Kenneth C. K.
On the Geometry of the Moduli Space of Real Binary Octics
The moduli space of smooth real binary octics has five connected components. They parametrize the real binary octics whose defining equations have $0,\dots,4$ complex-conjugate pairs of roots respectively. We show that each of these five components has a real hyperbolic structure in the sense that each is isomorphic as a real-analytic manifold to the quotient of an open dense subset of $5$-dimensional real hyperbolic space $\mathbb{RH}^5$ by the action of an arithmetic subgroup of $\operatorname{Isom}(\mathbb{RH}^5)$. These subgroups are commensurable to discrete hyperbolic reflection groups, and the Vinberg diagrams of the latter are computed.

Keywords:real binary octics, moduli space, complex hyperbolic geometry, Vinberg algorithm
Categories:32G13, 32G20, 14D05, 14D20

2. CJM 2009 (vol 61 pp. 109)

Coskun, Izzet; Harris, Joe; Starr, Jason
The Ample Cone of the Kontsevich Moduli Space
We produce ample (resp.\ NEF, eventually free) divisors in the Kontsevich space $\Kgnb{0,n} (\mathbb P^r, d)$ of $n$-pointed, genus $0$, stable maps to $\mathbb P^r$, given such divisors in $\Kgnb{0,n+d}$. We prove that this produces all ample (resp.\ NEF, eventually free) divisors in $\Kgnb{0,n}(\mathbb P^r,d)$. As a consequence, we construct a contraction of the boundary $\bigcup_{k=1}^{\lfloor d/2 \rfloor} \Delta_{k,d-k}$ in $\Kgnb{0,0}(\mathbb P^r,d)$, analogous to a contraction of the boundary $\bigcup_{k=3}^{\lfloor n/2 \rfloor} \tilde{\Delta}_{k,n-k}$ in $\kgnb{0,n}$ first constructed by Keel and McKernan.

Categories:14D20, 14E99, 14H10

3. CJM 2003 (vol 55 pp. 766)

Kerler, Thomas
Homology TQFT's and the Alexander--Reidemeister Invariant of 3-Manifolds via Hopf Algebras and Skein Theory
We develop an explicit skein-theoretical algorithm to compute the Alexander polynomial of a 3-manifold from a surgery presentation employing the methods used in the construction of quantum invariants of 3-manifolds. As a prerequisite we establish and prove a rather unexpected equivalence between the topological quantum field theory constructed by Frohman and Nicas using the homology of $U(1)$-representation varieties on the one side and the combinatorially constructed Hennings TQFT based on the quasitriangular Hopf algebra $\mathcal{N} = \mathbb{Z}/2 \ltimes \bigwedge^* \mathbb{R}^2$ on the other side. We find that both TQFT's are $\SL (2,\mathbb{R})$-equivariant functors and, as such, are isomorphic. The $\SL (2,\mathbb{R})$-action in the Hennings construction comes from the natural action on $\mathcal{N}$ and in the case of the Frohman--Nicas theory from the Hard--Lefschetz decomposition of the $U(1)$-moduli spaces given that they are naturally K\"ahler. The irreducible components of this TQFT, corresponding to simple representations of $\SL(2,\mathbb{Z})$ and $\Sp(2g,\mathbb{Z})$, thus yield a large family of homological TQFT's by taking sums and products. We give several examples of TQFT's and invariants that appear to fit into this family, such as Milnor and Reidemeister Torsion, Seiberg--Witten theories, Casson type theories for homology circles {\it \`a la} Donaldson, higher rank gauge theories following Frohman and Nicas, and the $\mathbb{Z}/p\mathbb{Z}$ reductions of Reshetikhin--Turaev theories over the cyclotomic integers $\mathbb{Z} [\zeta_p]$. We also conjecture that the Hennings TQFT for quantum-$\mathfrak{sl}_2$ is the product of the Reshetikhin--Turaev TQFT and such a homological TQFT.

Categories:57R56, 14D20, 16W30, 17B37, 18D35, 57M27

4. CJM 2000 (vol 52 pp. 1235)

Hurtubise, J. C.; Jeffrey, L. C.
Representations with Weighted Frames and Framed Parabolic Bundles
There is a well-known correspondence (due to Mehta and Seshadri in the unitary case, and extended by Bhosle and Ramanathan to other groups), between the symplectic variety $M_h$ of representations of the fundamental group of a punctured Riemann surface into a compact connected Lie group~$G$, with fixed conjugacy classes $h$ at the punctures, and a complex variety ${\cal M}_h$ of holomorphic bundles on the unpunctured surface with a parabolic structure at the puncture points. For $G = \SU(2)$, we build a symplectic variety $P$ of pairs (representations of the fundamental group into $G$, ``weighted frame'' at the puncture points), and a corresponding complex variety ${\cal P}$ of moduli of ``framed parabolic bundles'', which encompass respectively all of the spaces $M_h$, ${\cal M}_h$, in the sense that one can obtain $M_h$ from $P$ by symplectic reduction, and ${\cal M}_h$ from ${\cal P}$ by a complex quotient. This allows us to explain certain features of the toric geometry of the $\SU(2)$ moduli spaces discussed by Jeffrey and Weitsman, by giving the actual toric variety associated with their integrable system.

Categories:58F05, 14D20

5. CJM 1998 (vol 50 pp. 581)

Kamiyama, Yasuhiko
The homology of singular polygon spaces
Let $M_n$ be the variety of spatial polygons $P= (a_1, a_2, \dots, a_n)$ whose sides are vectors $a_i \in \text{\bf R}^3$ of length $\vert a_i \vert=1 \; (1 \leq i \leq n),$ up to motion in $\text{\bf R}^3.$ It is known that for odd $n$, $M_n$ is a smooth manifold, while for even $n$, $M_n$ has cone-like singular points. For odd $n$, the rational homology of $M_n$ was determined by Kirwan and Klyachko [6], [9]. The purpose of this paper is to determine the rational homology of $M_n$ for even $n$. For even $n$, let ${\tilde M}_n$ be the manifold obtained from $M_n$ by the resolution of the singularities. Then we also determine the integral homology of ${\tilde M}_n$.

Keywords:singular polygon space, homology
Categories:14D20, 57N65

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