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Questions tagged [character-varieties]

moduli of representations (Betti moduli), moduli of Higgs bundles (Dolbeault moduli), moduli of connections (de Rham moduli space), moduli of principal bundles (Čech moduli space), moduli of polygons, moduli of geometric structures, spin networks, skein theory, A-polynomial, higher Teichmüller theory

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Representation functor on modules

Let $k$ be a field and $A$ a unital associative $k$-algebra. The representation functor associates, to each object in non-commutative geometry, a genuine geometric object on the representation variety ...
Qwert Otto's user avatar
9 votes
2 answers
598 views

Is a local system on a surface determined by simple closed loops?

Let $\Sigma$ be a closed oriented topological surface of genus $g\geq 2$, and let $\mathfrak{X}_n$ denote the $\mathrm{SL}_n$-character variety of $\pi_1(\Sigma)$, i.e. $$ \mathfrak{X}_n= \mathrm{Hom}(...
Josh Lam's user avatar
  • 254
7 votes
1 answer
272 views

Hyperbolic homology spheres with infinite $\mathrm{SL}_2(\mathbb{C})$ character variety

$\DeclareMathOperator\SL{SL}$By the celebrated results of Culler and Shalen, a closed $3$-manifold contains an incompressible surface if its $\SL_2(\mathbb{C})$ character variety is infinite. Now, for ...
Renaud Detcherry's user avatar
2 votes
1 answer
288 views

Orbit closures in smooth irreducible components

$\DeclareMathOperator\mod{mod}\DeclareMathOperator\GL{GL}$ Consider a basic connected finite dimensional algebra $A$ over an algebraically closed field $k$, with $n$ distinct isomorphism classes of ...
Kaveh's user avatar
  • 493
8 votes
1 answer
548 views

Why is the $\operatorname{GL}_n$ character variety "cohomologically" the product of the $\operatorname{PGL}_n$ character variety and a torus?

$\def\CC{\mathbb{C}}\def\ZZ{\mathbb{Z}}\def\GL{\operatorname{GL}}$This question is about an assertion in Mixed Hodge polynomials of character varieties, by Hausel and Rodriguez-Villegas. Fix positive ...
David E Speyer's user avatar
10 votes
2 answers
992 views

Character variety of the free group

A classical result of Fricke--Klein--Vogt from the late 1800s implies that the character variety $\chi_\mathbb{C}$ associated to the free group $F_2$ and the algebraic group $\mathrm{SL}_2(\mathbb{C})$...
Dr. Evil's user avatar
  • 2,751
8 votes
2 answers
340 views

Distinct knots with same $A$-polynomial

Are there two non-isotopic knots $K,K'$ in $S^3$ with the same $\mathrm{SL}_2(\mathbb C)$ $A$-polynomials? If it's an open problem, has anyone suggested a method for finding them, or a reason why no ...
Calvin McPhail-Snyder's user avatar
3 votes
1 answer
247 views

Is the irreducible locus of the character variety a principal bundle in Zariski topology?

Let $\Sigma$ be a compact orientable surface and let $G$ be a reductive algebraic group (say, $G=\mathrm{SL}_n(\mathbb{C})$ for simplicity). The representation variety is $$ X_G(\Sigma) = \mathrm{Hom}(...
a_g's user avatar
  • 507
9 votes
2 answers
472 views

Orbit of an irreducible representation of a surface group under that action of the mapping class group

Let $F$ be a closed oriented surface of negative Euler characteristic. Let $X^i(F)$ be the subset of the $SL_2\mathbb{C}$-character variety of the fundamental group of $F$ corresponding to irreducible ...
Charlie Frohman's user avatar
1 vote
1 answer
204 views

Lie bracket on the complex valued functions of the space of representations of a Riemann surface

Let $S$ be a closed surface and $G$ be a reductive Lie group. Goldman (Invariant functions on Lie groups and Hamiltonian flows of surface group representations) proved that, for a fairly general class ...
tessellation's user avatar
12 votes
3 answers
1k views

SL(2, C)-representation of a knot

When studying knot theory I often encounter $SL(2, \mathbb{C})$-representation of knots (of the knot group) or the $SL(2, \mathbb{C})$ character variety of a knot group. But I just don't seem to ...
Jake B.'s user avatar
  • 1,465
10 votes
1 answer
434 views

A question about dimension of SL(2,C) character variety of knot group

It is known that if there isn't a closed essential surface in $S^3 \setminus K$, the dimension of $SL(2,\mathbb C)$ character variety is $1$. (In fact, it holds for a general 3-manifold, not only for ...
Seonhwa  Kim's user avatar
10 votes
1 answer
706 views

Moduli space of flat connections of Lie group over a 2-torus

We know that the moduli space of SU($N$) principal bundle's flat connections over a torus, is equivalent to a complex projective space $\mathbb{P}^{N-1}$ Namely, $$ M_{\rm flat}=\mathbb{E} / {S}_N = \...
wonderich's user avatar
  • 10.5k
5 votes
1 answer
320 views

The ¨irreducible¨ representation variety of surface group

Let $S$ be a closed surface of genus larger than 1, $G$ be a compact, simply connected simple Lie group with finite center. Consider the representation variety $M(S,G)=Rep(\pi_1(S), G)$. Witten´s ...
BiM's user avatar
  • 325
3 votes
1 answer
180 views

Kernel of restriction for ring of functions on reductive groups

Let $H \subset G$ be an inclusion of reductive groups over an algebraically closed field $k$ of char $0$. For simplicity, let's assume that $G$ is split and $H$ contains a maximal torus for $G$. Then ...
user125639's user avatar
2 votes
1 answer
203 views

Metric on moduli space of semistable principal G-bundles on curves

Let $X$ be an irreducible smooth projective curve over $\mathbb{C}$. Let $G$ be a connected reductive linear algebraic group over $\mathbb{C}$. Let ${\rm M}_{G,X}$ be the moduli space of semistable ...
user124771's user avatar
6 votes
1 answer
326 views

Compactifications of SL(2)-character varieties of surfaces

Thurston compactified the Teichmüller space ${\cal T}(F)$ of a closed, oriented surface $F$ with a piecewise-linear sphere. Furthermore, as far as I understand, its linear pieces have natural ...
Adam's user avatar
  • 2,390
3 votes
0 answers
161 views

Question on Neumann-Zagier Symplectic matrix of an ideal triangulation of one cusped 3-manifold

For a knot complement $M\backslash K$ on a general closed 3-manifold $M$, the gluing equations are given by ($k$ is the number of ideal tetrahedra in an ideal triangulation of $M\backslash K$) $c_I:=\...
강동민's user avatar
  • 115
2 votes
0 answers
124 views

Non Seifert incompressible surfaces detected by ideal points

Given a 3-manifold with toric boundary, the Culler-Shalen theory associates an incompressible surface to any ideal point of its character variety. From the proof of the Neuwirth conjecture, one knows ...
Léo's user avatar
  • 223
9 votes
1 answer
240 views

Classification of geometric structures through character varieties

Under what general assumptions $(G,X)$-geometric structures on a manifold $M$ are classified by their holonomies, yielding an injection $$\Psi: \{(G,X)\text{-structures on M}\} \to H(\pi_1(M),G)/G ?$$ ...
Adam's user avatar
  • 2,390
8 votes
2 answers
591 views

Flat connections on 3-manifold with boundary

Suppose $Y$ is a 3-manifold and the boundary $\Sigma:=\partial Y$ is non-empty. Let $G$ be a Lie group with trivial center. Let $\overline {\mathcal A}_{flat}(\Sigma)$ and $\overline {\mathcal A}_{...
Anon's user avatar
  • 778
31 votes
4 answers
2k views

Why do people study representations of 3-manifold groups into $SL(n,\mathbb{C})$?

Varieties of representations and characters of $3$-manifold groups in $SL(2,\mathbb{C})$ have been intensively studied. They have provided tools to identify geometric structures on manifolds, and are ...
Daniel Moskovich's user avatar
9 votes
3 answers
1k views

Moduli spaces of connections as representation spaces

It is well known that the moduli space of flat connections over a closed manifold $M$ can be identified with the representation space $Hom(\pi_1(M), G) / G$. Furthermore, Atiyah and Bott (1983) ...
Tobias Diez's user avatar
  • 5,824
10 votes
7 answers
1k views

Reference on representations of knot groups

Recently, I was studying knot groups and I wanted to learn some more material about them (e.g. their representations). "Knots" by Burde and Zieschang discusses some material but it is not entirely ...
Karatuğ Ozan Bircan's user avatar
13 votes
1 answer
1k views

Representation varieties of 3-manifold groups in $\mathrm{SL}(n,\mathbb{C})$

I am looking at the variety of representations of the fundamental group of a hyperbolic 3-manifold into $\mathrm{SL}(n,\mathbb{C})$: $$\mathrm{Hom}(\pi_1(M), \mathrm{SL}(n,{\mathbb C}))$$ It is known ...
ThiKu's user avatar
  • 10.4k
6 votes
0 answers
313 views

Can the analytic arc of an irred. $\mathrm{SL}_2(\mathbb{C})$-character always be lifted to an analytic arc of an irred. representation?

Is there an example of an irreducible and boundary irreducible $3$-manifold $M$ with torus boundary and a non-abelian representation $\rho: \pi_1(M) \to \mathrm{SL}_2(\mathbb{C})$, a non-constant ...
christian's user avatar
  • 481
3 votes
1 answer
323 views

When is an irreducible $\mathrm{SL}_2(\mathbb{C})$ representation of a cusped hyperbolic 3-manifold scheme reduced or smooth?

Let $M$ be an orientable cusped hyperbolic 3-manifold. Let $\rho \in \mathrm{Hom}(\pi_1(M),\mathrm{SL}_2(\mathbb{C}))$ be an irreducible representation. Is $\rho$ scheme reduced ? What can ...
christian's user avatar
  • 481
3 votes
1 answer
927 views

Representation variety vs. space of flat connections

The holonomy provides a bijection from the space of flat $G$-connections (modulo gauge equivalence) on a trivial $G$-bundle over $M$ to a connected component of the representation variety $Hom(\...
ThiKu's user avatar
  • 10.4k
1 vote
1 answer
269 views

Algebraicness of trace field of finite volume hyperbolic 3-manifold and dimension of $\mathrm{SL}(2,\mathbb{C})$-character variety

Does the following statement: "Let $G$ be a finitely generated group and let $X(G)$ be the $SL(2,\mathbb{C})$-character variety of $G$. Suppose $X(G)$ contains an irreducible component $X_0$...
christian's user avatar
  • 481
3 votes
1 answer
275 views

Relation between the Character variety of a knot $K\subset M$ and that of $M$

Suppose there is a knot $K\subset M$, where $M$ is a closed 3-manifold. What's the relation between $\chi(\pi_{1}(M-K))$ and $\chi(\pi_{1}(M))$? Note: $\chi(G)$ means the $\text{SL}_{2}(C)$-...
Lin Jianfeng's user avatar
15 votes
1 answer
1k views

Can the SL_2 character variety of a three-manifold be nonreduced?

Let $M^3$ be a three-manifold and consider the representation variety and the character variety of $M$: $$Y=\operatorname{Hom}(\pi_1(M^3),\operatorname{SL}(2,\mathbb C))$$ $$X=\operatorname{Hom}(\pi_1(...
John Pardon's user avatar
  • 18.7k
12 votes
1 answer
2k views

Rank two vector bundles on a curve of genus two

I recently learned of an interesting result of Narasimhan and Ramanan from 1969, which says that moduli space of rank two vector bundles with trivial determinant on a curve $X$ of genus two is ...
John Pardon's user avatar
  • 18.7k
9 votes
1 answer
609 views

Character varieties of finitely generated groups

Consider the following situation: $\Gamma_0\leq\Gamma$ are both finitely generated groups and $\Gamma_0$ has finite index in $\Gamma$. The restriction gives a well defined map between the character ...
Benoît's user avatar
  • 190
10 votes
1 answer
897 views

What is (explicitly) known about the SL(n,C) character varieties of 3-manifolds?

The $SL(2,{\bf C})$ character variety of a 3-manifold with 1-cusp $M$ (like a knot complement in the 3-sphere) essentially coincide with the variety defined by the A-polynomial. Those polynomials are ...
Gaetan Borot's user avatar
11 votes
2 answers
490 views

Cohomology of $T^n/W$ for compact Lie groups

Let $G$ be a compact, connected and simply connected Lie group. Let $T\subset G$ be a maximal torus and let $W$ be the corresponding Weyl group. Then we have the diagonal action of $W$ on $T^{n}$ ...
José Manuel Gómez's user avatar
15 votes
0 answers
1k views

Representations of quantum groups at roots of unity

I'm interested in the semisimplified category of representations of a quantum group at a root of unity. I've heard that simple objects in this category correspond to certain "integral" conjugacy ...
John Pardon's user avatar
  • 18.7k
13 votes
0 answers
591 views

Generalization of Witten's computation of the volume of moduli space

Let $\Sigma$ be a Riemann surface, and let $X:=\operatorname{Hom}(\pi_1(\Sigma),\operatorname{SU}(2))/\operatorname{SU}(2)$ be the $\operatorname{SU}(2)$ character variety of $\pi_1(\Sigma)$. There ...
John Pardon's user avatar
  • 18.7k
7 votes
2 answers
684 views

Deriving the Hilbert spaces for Chern-Simons TQFTs with complex gauge group

One method for finding the Hilbert spaces corresponding to surfaces in Chern-Simons TQFT is by geometrically quantizing the phase space, which is just the character variety of the surface. I know that ...
Blake's user avatar
  • 1,025
3 votes
1 answer
517 views

Which bundles does the character variety parameterize?

For any Riemann surface with punctures $C$, and Lie group $G$, the character variety is the space of maps $\mathrm{Hom}(\pi_1(C), G)$. I know that if $G= S_n$ (not a lie group), then $\mathrm{Hom}(\...
john mangual's user avatar
  • 22.8k
4 votes
0 answers
210 views

Is tensor product flat with respect to the Hitchin connection?

Let $M$ be a compact symplectic manifold equipped with a line bundle $\mathcal L$ with curvature $\omega$. Denote by $H^0(M,\mathcal L)$ the space of smooth global sections of $\mathcal L$ (this ...
John Pardon's user avatar
  • 18.7k
4 votes
1 answer
697 views

How does one relate the monodromy of the KZ equations with the WRT representation of the braid group?

The KZ equations on the configuration space of $n$ distinct points in $\mathbb C$ give rise to a representation of $B_n$ on $V^{\otimes n}$, where $V$ is any given representation of $SL(2)$ (we'll ...
John Pardon's user avatar
  • 18.7k
4 votes
0 answers
358 views

Do real polarization and Kahler polarization of character varieties of closed surfaces give equivalent representations of the Mapping Class Group?

This is a question about the Witten--Reshetikhin--Turaev representations of the mapping class group of a closed surface $\Sigma_g$. For simplicity, we'll stick to the case $G=SU(2)$. These ...
John Pardon's user avatar
  • 18.7k
3 votes
1 answer
606 views

How to interpret sections over the $\mathrm{SU}(2)$ character variety as sections over the $\mathrm{SL}(2,\mathbb{C})$ character variety?

The motivation for this question comes from the Volume Conjecture of Kashaev-Murakami-Murakami. The Jones family of invariants of knots and $3$-manifolds can all be defined using $\mathrm{SU}(2)$ and ...
John Pardon's user avatar
  • 18.7k
7 votes
2 answers
654 views

What is the state in the WRT TQFT associated to a handlebody?

Let $Y^3$ be a handlebody with boundary $\Sigma$. By definition, there is some associated vector $v_{WRT}(Y^3)\in Z(\Sigma)$, the (finite dimensional) Hilbert space associated to $\Sigma$ by the ...
John Pardon's user avatar
  • 18.7k
14 votes
1 answer
880 views

Is there an algebraic description of Yang-Mills measure?

Consider $X=\operatorname{Hom}(\pi,\mathrm{SL}(2,\mathbb C))/\! \!/\mathrm{SL}(2,\mathbb C)$ and $Y=\operatorname{Hom}(\pi,\mathrm{SU}(2))/\mathrm{SU}(2)$, where $\pi$ is a surface group. Note that ...
John Pardon's user avatar
  • 18.7k
11 votes
1 answer
1k views

How nice are representation varieties of Fuchsian groups?

Background Let $S_{g,n}$ be an oriented surface of genus $g$, with $n$ punctures. We explicitly prohibit the non-hyperbolic cases: $g=0$, $n=0,1,2$. $g=1$, $n=0$. Let $\Gamma$ be the fundamental ...
Greg Muller's user avatar
14 votes
1 answer
1k views

Moduli space of semistable bundles

It is well-known that the space of $S$-equivalence classes of rank 2 semistable holomorphic vector bundles with trivial determinant on a genus 2 Riemann surface $M$ is $CP^3$ (more concretely $PH^0(...
Sebastian's user avatar
  • 6,825
12 votes
3 answers
3k views

Zariski tangent spaces to representation varieties

In Bill Goldman's paper "The Symplectic Nature of the Fundamental Groups of Surfaces" (Advances, 54, 200-225, '84) it is stated that the "Zariski tangent space" to a representation space Hom$(\pi, G)/...
Dan Ramras's user avatar
  • 8,803
3 votes
2 answers
601 views

SU(2) representations of alternating knot groups

Suppose that $K$ is an $\textit{alternating}$ knot in $S^3$, and let $R_0$ be the space of homomorphisms from $\pi_1(S^3 - K)\to SU(2)$ which send meridians to trace free matrices. Denote the subset ...
Sam Lewallen's user avatar
  • 1,129