Mapping Class Group Research Articles

Extending periodic maps on surfaces over the 4-sphere

Let [Formula: see text] be the closed orientable surface of genus [Formula: see text]. We address the problem to extend torsion elements of the mapping class group [Formula: see text] over the 4-sphere [Formula: see text]. Let [Formula: see text] be a torsion element of maximum order in [Formula: see text]. Results including: (1) For each [Formula: see text], [Formula: see text] is periodically extendable over [Formula: see text] for some non-smooth embedding [Formula: see text], and not periodically extendable over [Formula: see text] for any smooth embedding [Formula: see text]. (2) For each [Formula: see text], [Formula: see text] is extendable over [Formula: see text] for some smooth embedding [Formula: see text] if and only if [Formula: see text]. (3) Each torsion element of order [Formula: see text] in [Formula: see text] is extendable over [Formula: see text] for some smooth embedding [Formula: see text] if either (i) [Formula: see text] and [Formula: see text] is even; or (ii) [Formula: see text] and [Formula: see text]; or (iii) [Formula: see text]. Moreover, the conditions on [Formula: see text] in (i) and (ii) cannot be removed.

A small generating set for the balanced superelliptic handlebody group

The balanced superelliptic handlebody group is the normalizer of the transformation group of the balanced superelliptic covering space in the handlebody group of the total space. We prove that the balanced superelliptic mapping class group is generated by four elements. To prove this, we also proved that the liftable Hilden group is generated by three elements. This generating set for the liftable Hilden group is minimal except for some hyperelliptic cases and the generating set for the balanced superelliptic mapping class group above is also minimal for several cases.

On the surjectivity of the symplectic representation of the mapping class group

In this note, we study the symplectic representation of the mapping class group. In particular, we discuss the surjecivity of the representation restricted to certain mapping classes. It is well-known that the representation itself is surjective. In fact the representation is still surjective after restricting on pseudo-Anosov mapping classes. However, we show that the surjectivity does not hold when the representation is restricted on orientable pseudo-Anosovs, even after reducing its codomain to integer symplectic matrices with a bi-Perron leading eigenvalue. In order to prove the non-surjectivity, we explicitly construct an infinite family of symplectic matrices with a bi-Perron leading eigenvalue which cannot be obtained as the symplectic representation of an orientable pseudo-Anosov mapping class.

Ergodicity of the mapping class group action on Deroin–Tholozan representations

This note investigates the dynamics of the mapping class group action on compact connected components of relative character varieties of surface group representations into PSL(2, \mathbb{R} ), discovered by Deroin and Tholozan. We apply symplectic methods developed by Goldman and Xia to prove that the action is ergodic.

On [formula omitted]-mapping class monoids

In this paper, we introduce PM-mapping class monoids. Braid groups and mapping class groups have many features in common. Similarly to the notion of braid PM-monoid, PM-mapping class monoid is defined. This construction is an analogy of inverse mapping class monoid defined by R. Karoui and V. V. Vershinin. As the main result, we give the analog of the Dehn-Nilsen-Baer theorem.

Framed mapping class groups and the monodromy of strata of abelian differentials

This paper investigates the relationship between strata of abelian differentials and various mapping class groups afforded by means of the topological monodromy representation. Building off of prior work of the authors, we show that the fundamental group of a stratum surjects onto the subgroup of the mapping class group which preserves a fixed framing of the underlying Riemann surface, thereby giving a complete characterization of the monodromy group. In the course of our proof we also show that these “framed mapping class groups” are finitely generated (even though they are of infinite index) and give explicit generating sets.

Small exotic 4-manifolds and symplectic Calabi–Yau surfaces via genus-3 pencils

We explicitly produce symplectic genus-3 Lefschetz pencils (with base points), whose total spaces are homeomorphic but not diffeomorphic to rational surfaces CP^2 # p (-CP^2) for p= 7, 8, 9. We then give a new construction of an infinite family of symplectic Calabi-Yau surfaces with first Betti number b_1=2,3, along with a surface with b_1=4 homeomorphic to the 4-torus. These are presented as the total spaces of symplectic genus-3 Lefschetz pencils we construct via new positive factorizations in the mapping class group of a genus-3 surface. Our techniques in addition allow us to answer in the negative a question of Korkmaz regarding the upper bound on b_1 of a genus-g fibration.

Weakly framed surface configurations, Heisenberg homology, and mapping class group action

We obtain representations of the \(\texttt{f}\)-based mapping class group of oriented punctured surfaces from an action of mapping classes on Heisenberg homologies of a circle bundle over surface configurations.

Ergodic invariant measures on the space of geodesic currents

Let S be a compact, connected, oriented surface, possibly with boundary, of negative Euler characteristic. In this article we extend Lindenstrauss–Mirzakhani’s and Hamenstädt’s classification of locally finite mapping class group invariant ergodic measures on the space of measured laminations ℳℒ(S) to the space of geodesic currents 𝒞(S), and we discuss the homogeneous case. Moreover, we extend Lindenstrauss–Mirzakhani’s classification of orbit closures to 𝒞(S). Our argument relies on their results and on the decomposition of a current into a sum of three currents with isotopically disjoint supports: a measured lamination without closed leaves, a simple multi-curve and a current that binds its hull.

Normal subgroups of big mapping class groups

Let S S be a surface and let Mod ⁡ ( S , K ) \operatorname {Mod}(S,K) be the mapping class group of S S permuting a Cantor subset K ⊂ S K \subset S . We prove two structure theorems for normal subgroups of Mod ⁡ ( S , K ) \operatorname {Mod}(S,K) . (Purity:) if S S has finite type, every normal subgroup of Mod ⁡ ( S , K ) \operatorname {Mod}(S,K) either contains the kernel of the forgetful map to the mapping class group of S S , or it is ‘pure’ — i.e. it fixes the Cantor set pointwise. (Inertia:) for any n n element subset Q Q of the Cantor set, there is a forgetful map from the pure subgroup PMod ⁡ ( S , K ) \operatorname {PMod}(S,K) of Mod ⁡ ( S , K ) \operatorname {Mod}(S,K) to the mapping class group of ( S , Q ) (S,Q) fixing Q Q pointwise. If N N is a normal subgroup of Mod ⁡ ( S , K ) \operatorname {Mod}(S,K) contained in PMod ⁡ ( S , K ) \operatorname {PMod}(S,K) , its image N Q N_Q is likewise normal. We characterize exactly which finite-type normal subgroups N Q N_Q arise this way. Several applications and numerous examples are also given.

The polyhedral tree complex

The tree complex is a simplicial complex defined in recent work of Belk, Lanier, Margalit, and Winarski with applications to mapping class groups and complex dynamics. This article introduces a connection between this setting and the convex polytopes known as associahedra and cyclohedra. Specifically, we describe a characterization of these polytopes using planar embeddings of trees and show that the tree complex is the barycentric subdivision of a polyhedral cell complex for which the cells are products of associahedra and cyclohedra.Mathematics Subject Classifications: 05C05, 05C10, 20F65, 52B11Keywords: Associahedra, cyclohedra, planar trees, mapping class groups

Generalized Long–Moody functors

In this paper, we generalize the principle of the Long-Moody construction for representations of braid groups to other groups, such as mapping class groups of surfaces. Namely, we introduce endofunctors over a functor category that encodes representations of a family of groups. They are called Long-Moody functors and provide new representations. In this context, notions of polynomial functors are defined and play an important role in the study of homological stability. We prove that, under additional assumptions, a Long-Moody functor increases the very strong and weak polynomial degrees of functors by one.

Geometric realizations of cyclic actions on surfaces: II

Let $$\mathrm {Mod}(S_g)$$ denote the mapping class group of the closed orientable surface $$S_g$$ of genus $$g\ge 2$$ . Given a finite subgroup H of $$\mathrm {Mod}(S_g)$$ , let $$\mathrm {Fix}(H)$$ denote the set of fixed points induced by the action of H on the Teichmüller space $$\mathrm {Teich}(S_g)$$ . When H is cyclic with $$|H| \ge 3$$ , we show that $$\mathrm {Fix}(H)$$ admits a decomposition as a product of two-dimensional strips at least one of which is of bounded width. For an arbitrary H with at least one generator of order $$\ge 3$$ , we derive a computable optimal upper bound for the restriction $$\mathrm {sys}: \mathrm {Fix}(H) \rightarrow \mathbb {R}^+$$ of the systole function. Furthermore, we show that in such a case, $$\mathrm {Fix}(H)$$ is not symplectomorphic to the Euclidean space of the same dimension. Finally, we apply our theory to recover three well known results, namely: (a) Harvey’s result giving the dimension of $$\mathrm {Fix}(H)$$ , (b) Gilman’s result that H is irreducible if and only if the corresponding orbifold is a sphere with three cone points, and (c) the Nielsen realization theorem for cyclic groups.

Higher spin JT gravity and a matrix model dual

We propose a generalization of the Saad-Shenker-Stanford duality relating matrix models and JT gravity to the case in which the bulk includes higher spin fields. Using a PSL(N, ℝ) BF theory we compute the disk and generalization of the trumpet partition function in this theory. We then study higher genus corrections and show how this differs from the usual JT gravity calculations. In particular, the usual quotient by the mapping class group is not enough to ensure finite answers and so we propose to extend this group with additional elements that make the gluing integrals finite. These elements can be thought of as large higher spin diffeomorphisms. The cylinder contribution to the spectral form factor then behaves as TN−1 at late times T, signaling a deviation from conventional random matrix theory. To account for this deviation, we propose that the bulk theory is dual to a matrix model consisting of N − 1 commuting matrices associated to the N − 1 conserved higher spin charges.We find further evidence for the existence of the additional mapping class group elements by interpreting the bulk gauge theory geometrically and employing the formalism developed by Gomis et al. in the nineties. This formalism introduces additional (auxiliary) boundary times so that each conserved charge generates translations in those new directions. This allows us to find an explicit description for the PSL(3, ℝ) Schwarzian theory for the disk and trumpet and view the additional mapping class group elements as ordinary Dehn twists, but in higher dimensions.

Torsion generators of the twist subgroup

We show that the twist subgroup of the mapping class group of a closed connected nonorientable surface of genus $g\geq13$ can be generated by two involutions and an element of order $g$ or $g-1$ depending on whether $g$ is odd or even respectively.

Mapping Class Group Representations Derived from Stated Skein Algebras

We construct finite-dimensional projective representations of the mapping class groups of compact connected oriented surfaces having one boundary component using stated skein algebras.

Strong homotopy induced by adjacency structure

This paper generalizes the concept of SA-homotopy in finite topological adjacency category, which is introduced in our previous work, to graph category and discusses its properties. We prove that every SA-strong deformation retract of a simple graph G could be obtained by removing trivial vertices one by one, which makes it possible to allow an iterative algorithm of finding all SA-strong deformation retracts of G. We also obtain that two simple graphs are SA-homotopy equivalent if and only if they have graph isomorphic cores. Compared with the graph homotopy transformation defined by S.T. Yau et al. and the s-homotopy transformation defined by R. Boulet et al., the main advantage of SA-homotopy transformation is that it could reflect correspondences between vertices, and hence it more accurately describe the transformation process than the graph homotopy transformation and s-homotopy transformation. As an application of SA-homotopy on graphs, we introduce the mapping class group of a graph, which also shows its advantage over the graph homotopy transformation and the s-homotopy transformation.

Mapping class groups with the Rokhlin property

We classify the connected orientable 2-manifolds whose mapping class groups have a dense conjugacy class. We also show that the mapping class group of a connected orientable 2-manifold has a comeager conjugacy class if and only if the mapping class group is trivial.

Mapping class group representations from Turaev-Viro TQFT for abelian groups

It is well known that (2 + 1) topological quantum field theories (TQFTs) induce representations for the mapping class groups (MCGs) of surfaces. In this paper, we work explicitly on the MCG representations of any genus from the Turaev-Viro TQFTs based on the category for the finite abelian group G and cocycle . As an application, we determine for torus the image of the MCG representation with the graphical calculus on the string-net diagram.

Asymptotically rigid mapping class groups, I : Finiteness properties of braided Thompson’s and Houghton’s groups

This article is dedicated to the study of asymptotically rigid mapping class groups of infinitely-punctured surfaces obtained by thickening planar trees. Such groups include the braided Ptolemy-Thompson groups $T^\sharp,T^\ast$ introduced by Funar and Kapoudjian, and the braided Houghton groups $\mathrm{br}H_n$ introduced by Degenhardt. We present an elementary construction of a contractible cube complex, on which these groups act with cube-stabilisers isomorphic to finite extensions of braid groups. As an application, we prove Funar-Kapoudjian's and Degenhardt's conjectures by showing that $T^\sharp,T^\ast$ are of type $F_\infty$ and that $\mathrm{br}H_n$ is of type $F_{n-1}$ but not of type $F_n$.