For a genus g surface with s > 0 punctures and 2g+s > 2, decorated Teichmuller space (DTeich) is a trivial R_+^s-bundle over the usual Teichmuller space, where the fiber corresponds to families of horocycles peripheral to each puncture. As proved by R. Penner, DTeich admits a mapping class group-invariant cell decomposition, which then descends to a cell decomposition of Riemann's moduli space. In this talk we introduce a new cellular bordification of DTeich which is also MCG-invariant, namely the space of filtered screens. After an appropriate quotient, we obtain a cell decomposition for a new compactification of moduli space, which is shown to be homotopy equivalent to the Deligne-Mumford compactification. This work is joint with R. Penner.

I will describe an upcoming paper with Goncalo Oliveira investigating the properties of Yang-Mills flow on base manifolds with restricted holonomy, generalizing known results from the 4-d and Kahler cases. We show that finite-time blowup is governed by the F^7 component of the curvature in the G_2 and Spin(7) cases, and by the appropriate curvature component in the remaining cases on Berger's list. Assuming that this component remains bounded along the flow, we show that the infinite-time bubbling set is calibrated by the defining (n-4)-form.

The Monopole (Bogomolnyi) equations are Geometric PDEs in 3 dimensions. In this talk I shall introduce a generalization of the monopole equations to both Calabi Yau and G_2 manifolds. I will motivate the possible relations of conjectural enumerative theories arising from "counting" monopoles and calibrated cycles of codimension 3. Then, I plan to state the existence of solutions and sketch how these examples are constructed.

A quasi-local mass has been a long sought after quantity in general relativity. A recent candidate has been the Liu-Yau mass. One can show that the Liu-Yau mass of any two-surface is the maximum of the Brown-York energy for that two-surface. This means that it has significant disadvantages as a mass. It is much better interpreted as an energy and I will show one way of doing so. The Liu-Yau mass is especially interesting in spherical geometries, where mass and energy are indistinguishable. For a spherical two-surface, it equals the minimum of the amount of energy at rest that one needs to put inside the two-surface to generate the given surface geometry. Thus it gives interesting information about the interior, something no other mass or energy function does.

Motivated by questions about the spectral geometry of hyperbolic manifolds, arising in number theory, we seek a lower bound for the first nonzero eigenvalue of the Laplace Beltrami operator on 1-forms on hyperbolic manifolds. We prove an analog of Cheeger's inequality. Joint work with Michael Lipnowski.

Compact 6-dimensional nearly Kähler manifolds are the cross-sections of Riemannian cones with holonomy G2. A long-standing problem has been the question of existence of complete nearly Kähler 6-manifolds besides the four known homogeneous ones. We resolve this problem by proving the existence of exotic (inhomogeneous) nearly Kähler structures on the 6-sphere and on the product of two 3-spheres. This is joint work with Mark Haskins, Imperial College London.

In joint work with Mark Stern, we introduce several families of filtrations on the space of vector bundles over a smooth projective variety. These filtrations are defined using the large k asymptotics of the kernel of the Dolbeault Dirac operator on a bundle twisted by the kth power of an ample line bundle. The filtrations measure the failure of the bundle to admit a holomorphic structure. We study compatibility under the Chern isomorphism of these filtrations with the Hodge filtration on cohomology.

After reviewing the proof of the Riemannian positive mass theorem in dimensions less than 8, I will briefly explain how to generalize the proof to slices of spacetime that are not time-symmetric. The basic idea is to replace minimal hypersurfaces by marginally outer-trapped hypersurfaces, and the main difficulty is to avoid using any minimization process. This is joint work with Eichmair, Huang, and Schoen.

The helicity of a vector field in R^3, an analog to linking number, measures the extent to which its flowlines coil and wrap around one another. Helicity turns out to be invariant under volume-preserving diffeomorphisms that are isotopic to the identity. Motivated by Bott-Taubes integration, we provide a new proof of this invariance using configuration spaces. We then present a new topological explanation for helicity, as a characteristic class. Among other results, this point of view allows us to completely characterize the diffeomorphisms under which helicity is invariant and give an explicit formula for the change in helicity under a diffeomorphism under which helicity is not invariant. (joint work with Jason Cantarella, U. of Georgia)

Over a field k, the zeroth homotopy group of the motivic sphere spectrum is given by the Grothendieck-Witt ring of symmetric bilinear forms GW(k). The Grothendieck-Witt ring GW(k) modulo the hyperbolic plane is isomorphic to the Witt ring of symmetric bilinear forms W(k) which further surjectively maps to Z/2. We may take motivic Eilenberg-Maclane spectra of Z/2, W(k) and GW(k). Voevodsky has computed the motivic Steenrod algebra of HZ/2 and solved the Bloch-Kato conjecture with its help. We move one step up in the above picture; we study the motivic Eilenberg-Maclane spectrum corresponding to the Witt ring and compute its dual Steenrod algebra.

In this talk, I will describe some recent work carried out with Rafe Mazzeo and Yanir Rubinstein, regarding the existence and nature of solutions to the problem of K\"{a}hler-Einstein metrics of constant negative curvature with certain prescribed singularities along a divisor in a compact, complex manifold. Earlier work of Aubin and of Yau established for the smooth compact case that for negative curvature, there are no obstructions beyond the immediate observation that the first Chern class of $M$ must be positive. I will include a brief outline of the method of solution in the smooth case. Since the publication of these earlier works, study of the negative case has focused on extension to various noncompact settings. In the situation described here, we considered metrics with conical singularities along a divisor. The most prominent feature of these metrics is that they are incomplete. Solution of this problem became possible recently when Simon Donaldson achieved a breakthrough in the linear theory.

TBA

I will discuss the question: When does a vector bundle admit a holomorphic structure? I will explore applications of Yang-Mills theory and geometric quantization to this problem.

If you take a surface in Euclidean space that is locally the graph of a C2 function, this induces a local coordinate system in which the metric tensor is merely C1. Geodesic flows are well defined when the metric tensor is C2, but there are lots of examples of metric tensors of class C^(2-epsilon) for which geodesics branch. Nevertheless, for the C2 surface mentioned above, the geodesic flow is well defined. This result has been noted several times. It has several proofs. One uses the fact that geodesic flows are well defined whenever the Ricci tensor is bounded. An important class of Gromov-Hausdorff limits of smooth Riemannian manifolds studied by Anderson and Cheeger puts a lower bound on the Ricci tensor (and the injectivity radius), and obtains a limiting manifold whose metric tensor is not quite C1. We will explore the question of whether the geodesic flow is well defined on such a limit, and also look at some other limits of smooth manifolds, with wilder behavior.

There is a natural relationship between moduli spaces of Riemann surfaces, mapping class groups of surfaces, and intersection patterns of simple closed curves on surfaces. In this talk, we describe an analogous relationship between moduli spaces of real algebraic curves, mapping class groups of surfaces with orientation reversing involutions, and intersection patterns of involution invariant simple closed curves on surfaces. After establishing these relationships, we obtain that the homology and cohomology groups of mapping class groups of surfaces with orientation reversing involutions satisfy duality relationships analogous to those for compact manifolds. We also obtain that higher homotopy groups associated to the moduli spaces of real algebraic curves relative to its boundary vanish in all degrees less than a determinable constant.

We first review the relation between wrapped Floer cohomology of co-core disks after Lagrangian handle attachment and the Legendrian DGA of the corresponding attaching spheres. Then we discuss a generalization of this result to the partially wrapped setting where the Legendrian dga should be enriched with loop space coefficients, and describe several cases when explicit calculations are possible via parallel copies or local coefficient systems. We also discuss applications of these ideas to the topology of Lagrangian fillings of Legendrian submanifolds. The talk reports on joint work with Y. Lekili.

The poset of hyperbolic structures on a group G is still very far from being understood and several questions remain unanswered. In this talk, I will speak about some new results that describe hyperbolic structures on the wreath product Gwr Z, for any group G. As a consequence, I answer two open questions regarding quasi-parabolic structures: I will give an example of a group G with an uncountable chain of quasi-parabolic structures and give examples of groups that have finitely many quasi-parabolic structures.

    An algebraic cycle homologous to zero on a variety leads to an extension of Hodge-theoretic data. In a variational context, the resulting section of a bundle of complex tori is called a normal function, and is used to study cycles modulo rational or algebraic equivalence.
    The archetype for interesting normal functions arises from the Ceresa cycle, consisting of the difference of two copies of a curve in its Jacobian. The profound geometric consequences of its existence are evidenced in work of Nori, Hain and (most recently) Totaro. In contrast, a theorem of Green and Voisin demonstrates the *absence* of normal functions arising from cycles on very general projective hypersurfaces of large enough degree.
    Inspired by recent work of Friedman-Laza on Hermitian variation of Hodge structure and Oort's conjecture on special subvarieties in the Torelli locus, R. Keast and I wondered about the existence of normal functions over etale neighborhoods of Shimura varieties. In this talk I will explain our classification of the cases where a Green-Voisin analogue does *not* hold, and where one expects interesting cycles (and generalized cycles) to occur. I will also give evidence that these predictions might be "sharp", and draw some geometric consequences.

One of the central conjectures in Kähler geometry is the Yau-Tian-Donaldson conjecture relating the existence of canonical Kähler metrics to algebro-geometric stability. A natural question is to ask what happens when such a metric does not exist, and here Kähler metrics of Poincaré type are expected to play an important role. These metrics are Kähler metrics defined on the complement of a divisor in a compact complex manifold and have a cusp-like singularity near the divisor. The blow-up theorem of Arezzo-Pacard and its generalizations give sufficient conditions for the blow-up of a compact Kähler manifold admitting a canonical metric to also carry such a metric. I will describe an extension of this result to the Poincaré type setting.

We will discuss the results of several joint ongoing projects (with subsets of collaborators Pierre Albin, Hans Christianson, Colin Guillarmou, Jason Metcalfe, Laurent Thomann and Michael Taylor), which explore the existence, stability and dynamics of nonlinear bound states and quasimodes on manifolds of both positive and negative curvature with various symmetry properties.

Knot concordance concerns the classification of knots in the 3-sphere that occur as the boundaries of embedded disks in the 4-ball. Unlike in higher dimensions, one obtains vastly different results depending on whether the disks are required to be smoothly embedded or merely locally flat (i.e. continuously embedded with a topological normal bundle); many tools arising from gauge theory and symplectic geometry can be used to illustrate this distinction. After surveying some of the recent progress in this area, I will discuss the extension of these questions to knots in 3-manifolds other than S^3. I will show how to use invariants coming from Heegaard Floer homology to obstruct not only smoothly embedded disks but also non-locally-flat piecewise-linear disks; this answers questions from the 1970s posed by Akbulut and Matsumoto. I will also discuss more recent results (joint with Jennifer Hom and Tye Lidman) giving infinitely many knots that are distinct up to non-locally-flat piecewise-linear concordance.

We give a new proof for the existence of mean curvature flow with surgery for 2-convex hypersurfaces. Our proof works in all dimensions, including mean convex surfaces in R^3. We also derive a-priori estimates for a more general class of flows, called (alpha,delta)-flows. This is joint work with Bruce Kleiner.

In recent years, there have been more and more connections between cubic 4folds and hyperkahler manifolds. The first instance of this was noticed by Beauville-Donagi, who showed that the Fano varieties of lines on a cubic 4folds X is holomorphic symplectic. This talk aims to describe another instance of this phenomenon, which is carried out in joint work with R. Laza and C. Voisin: given a general cubic 4fold X, Donagi and Markman showed in 1995 that the family of intermediate Jacobians of smooth hyperplane sections of X has a holomorphic symplectic form. I will present a proof of this conjecture, which uses relative compactified Prym varieties.

In this talk I will review the construction of the Lie algebra associated to the mapping class group of a (possibly decorated) surface and explain how this generalizes the Lie algebra associated to the pure braid group. I will also explain the analogue of the KZ-equation in the mapping class group case. In the second talk I will discuss filtrations of this Lie algebra associated to curve systems on the surface and their relation to handlebody groups.

I will exhibit a spectral sequence from the annular Khovanov homology of a 2-periodic link to that of its quotient, which in turn proves rank inequalities and decategorifies to polynomial congruences. While previous work used heavier algebraic machinery to prove this rank inequality in a particular sl_2 weight space grading, we instead mimic Borel's construction of equivariant cohomology and employ grading considerations to give a combinatorial proof of the rank inequality for all quantum and sl_2 weight space gradings. Curiously, the same methods suggest a similar spectral sequence relating the Khovanov homology of a 2-periodic link and the annular Khovanov homology of its quotient link. We'll discuss partial results on this front.