arXiv research

Reduces connectivity problem for genus-4 Heegaard surface in 3-sphere.

The paper provides examples of keen weakly reducible bridge spheres for links in b-bridge position.

Confirming the Powell Conjecture for genus-3 Heegaard splittings of the 3-sphere.

Study connects Powell Conjecture to reducing sphere complex's connectivity.

For a boundary-reducible $3$-manifold $M$ with $\partial M$ a genus $g$ surface, we show that if $M$ admits a genus $g+1$ Heegaard surface $S$, then the disk complex of $S$ is simply connected. Also we consider the connectedness of the complex of reducing spheres. We investigate the intersection of two reducing spheres…

Study of minimal immersions from a sphere to a complex hyperquadric.

Genus 3 Heegaard groups of lens space connected sums are finitely generated.

By the work of Harer, the reduced homology of the complex of curves is a fundamental cohomological object associated to all torsion free finite index subgroups of the mapping class group. We call this homology group the Steinberg module of the mapping class group. It was previously known that the curve complex has the …

Reduces weak reducing pairs to spheres in 3-sphere Heegaard surfaces.

A manifold which admits a reducible genus-$2$ Heegaard splitting is one of the $3$-sphere, $S^2 \times S^1$, lens spaces or their connected sums. For each of those splittings, the complex of Haken spheres is defined. When the manifold is the $3$-sphere, $S^2 \times S^1$ or the connected sum whose summands are lens spac…

Algorithm constructs reducing spheres for genus-2 Heegaard splitting of S^3.

Aramayona and Leininger have provided a "finite rigid subset" $\mathfrak{X}(Σ)$ of the curve complex $\mathscr{C}(Σ)$ of a surface $Σ= Σ^n_g$, characterized by the fact that any simplicial injection $\mathfrak{X}(Σ) \to \mathscr{C}(Σ)$ is induced by a unique element of the mapping class group $\mathrm{Mod}(Σ)$. In this…

We give a complete description of finite braid group orbits in Aff(C)-character varieties of the punctured Riemann sphere. This is performed thanks to a coalescence procedure and to the theory of finite complex reflection groups. We then derive consequences in the theory of differential equations. These concern algebra…

A new proof shows a reducing sphere can be obtained from a given sphere without surgeries.

Finite type for 3-manifolds with boundary.

Ancient solutions arise in the study of Ricci flow singularities. Motivated by the work of Fateev on 3-dimensional ancient solutions we construct high dimensional ancient solutions to Ricci flow on spheres and complex projective spaces as well as the twistor spaces over a compact quaternion-Kahler manifold. Differing f…

Finite set of Dehn twists describes genus-2 Goeritz group elements.

The paper describes the structure of injective LOT-complexes and proves they are aspherical.

Given a Coxeter system (W,S), there is an associated CW-complex, Sigma, on which W acts properly and cocompactly. We prove that when the nerve L of (W,S) is a flag triangulation of the 3-sphere, then the reduced $\ell^2$-homology of Sigma vanishes in all but the middle dimension.

Classifies critical complexes for embedding in 3-sphere.

New method finds non-orientable knotted surfaces in 4D.

Study contact structures on four-punctured spheres, finding infinitely many overtwisted monodromies.

Invalidation of a key lemma leaves the Powell Conjecture unresolved.

We define a "reduced" version of the knot Floer complex $CFK^-(K)$, and show that it behaves well under connected sums and retains enough information to compute Heegaard Floer $d$-invariants of manifolds arising as surgeries on the knot $K$. As an application to connected sums, we prove that if a knot in the three-sphe…

We construct the first known examples of nontrivial, normal, all pseudo-Anosov subgroups of mapping class groups of surfaces. Specifically, we construct such subgroups for the closed genus two surface and for the sphere with five or more punctures. Using the branched covering of the genus two surface over the sphere an…

Spheres in curve complexes are almost simply connected.

Finite rigid sets found in sphere complexes for some but not all cases.

New instanton invariants for rational homology spheres defined and shown to be functorial.

Many important equations of mathematical physics arise geometrically as geodesic equations on Lie groups. In this paper, we study an example of a geodesic equation, the two-component Hunter-Saxton (2HS) system, that displays a number of unique geometric features. We show that 2HS describes the geodesic flow on a manifo…

Disk complexes show 3-sphere surfaces are topologically minimal.

Kervaire's sphere-link is equivalent to a ribbon sphere-link, simplifying complex 2-complexes.

Survey on hypothetical complex structure on 6-sphere.

Research shows arc complex is not quasi-isometric to sphere complex.

No complex structure exists on a round 6-sphere.

We prove that all smooth sphere bundles that admit fiberwise 1/4-pinched metrics are induced bundles of vector bundles, so their structure groups reduce from the diffeomorphism group of the sphere to the orthogonal group. This result implies the existence of many smooth n-sphere bundles over a k-sphere that do not supp…

New surfaces described that are symmetric and solve a specific equation.

A conformal metric on a 4-ball induces on the boundary 3-sphere a conformal metric and a trace-free second fundamental form. Conversely, such a data on the 3-sphere is the boundary of a unique selfdual conformal metric, defined in a neighborhood of the sphere. In this paper we characterize the conformal metrics and tra…

We use the combinatorial techniques of graphs of intersection to study reducible Dehn surgeries on knots in the three-sphere. In particular, in the event that a reducible surgery on a knot K in the three-sphere of slope r produces a manifold with more than two connected summands, we show that r is bounded in absolute v…

We give new obstructions to the module structures arising in Heegaard Floer homology. As a corollary, we characterize the possible modules arising as the Heegaard Floer homology of an integer homology sphere with one-dimensional reduced Floer homology. Up to absolute grading shifts, there are only two. We use this coro…

By a theorem of Kirchhoff if the six sphere admits an almost complex structure then the seven sphere is parallelizable, more crucial, he exhibited an explicit global frame constructed out of the given almost complex structure. This result implicitly equips the seven sphere with a definite H-space multiplication. We pro…

Associated to any finite flag complex L there is a right-angled Coxeter group W_L and a contractible cubical complex Sigma_L (the Davis complex) on which W_L acts properly and cocompactly, and such that the link of each vertex is L. It follows that if L is a generalized homology sphere, then Sigma_L is a contractible h…

Researchers classify special curved spheres in a complex space.

Proves a conjecture about graph complexes without specific cycle lengths.

To reduce the label complexity in Agnostic Active Learning (A^2 algorithm), volume-splitting splits the hypothesis edges to reduce the Vapnik-Chervonenkis (VC) dimension in version space. However, the effectiveness of volume-splitting critically depends on the initial hypothesis and this problem is also known as target…

We discuss the integrability of orthogonal almost complex structures on Riemannian products of even-dimensional round spheres and give a partial answer to the question raised by E. Calabi concerning the existence of complex structures on a product manifold of a round 2-sphere and a round 4-sphere.

Normal and almost normal surfaces are essential tools for algorithmic 3-manifold topology, but to use them requires exponentially slow enumeration algorithms in a high-dimensional vector space. The quadrilateral coordinates of Tollefson alleviate this problem considerably for normal surfaces, by reducing the dimension …

Analytic torsions on contact spheres are calculated using Rumin complex.

Survey on finite group actions on CW-complexes homotopy to spheres.