# Differential Geometry Seminar Schedule for
Spring 2008

# Fridays 3:00 - 4:00pm, SH 6617

### 4/4, no meeting, see Distinguished Lectures

### 5/9, Robert McCann, University of Toronto
``Extremal doubly stochastic measures and optimal transport"

### 5/23, Rugang Ye, UCSB
``Nonlinear energy estimates for the heat equation, entropy functional,
and the Ricci flow on noncompact manifolds"

### 5/30, Julie Marie Rowlett, UCSB
``The Fundamental Gap Conjecture for Triangles"

Abstract: The Fundamental Gap Conjecture due to S. T. Yau and also M.
van de Berg states that for a convex planar domain of diameter d, the
first two positive eigenvalues of the Laplacian satisfy
$$\lambda_2 - \lambda_1 \geq \frac{3 \pi^2}{d^2}.$$
The gap between the first two eigenvalues has been studied by several
authors and while it is always interesting to understand the
interaction between the eigenvalues of a differential operator and the
geometry of the domain, beyond purely mathematical implications, the
gap also has physical implications. For example, the gap controls the
rate of collapse of any initial state toward a state dominated by the
first eigenvalue and is of central interest in statistical mechanics
and quantum field theory. The gap is important to numerical methods
because it can be used to control the rate of convergence of numerical
computation methods.
I will discuss joint work with Zhiqin Lu and present a "compactness
theorem" which shows that the fundamental gap for triangular domains
becomes unbounded as the domain collapses to a segment. This result
is a key step to proving the conjecture for triangular domains and for
our larger goal of proving the conjecture for all convex domains by
approximating polygonal domains.
### 6/6, Zhigang Han, University of Massachusetts
``A nonextension result on the spectral metric"

Abstract: The spectral metric is a bi-invariant metric on the Hamiltonian diffeomorphism group defined by Schwarz and Oh using Floer-theoretical method. In this talk, I will first explain the definition of the spectral metric for symplectically aspherical manifolds. Then I will explain why for certain symplectic manifolds, this metric does not extend to bi-invariant metric on the full group of symplectomorphisms.
# Differential Geometry Seminar Schedule for
Winter 2008

# Fridays 3:00 - 4:00pm, SH 6617

### 1/18, Seungsu Hwang, Chung-Ang University and visiting UCSB
``Critical points of the total scalar curvature functional"

Abstract: On a compact n-dimensional manifold M, it was shown that a critical point metric g of the total scalar curvature functional, restricted to the space of metrics with constant scalar curvature of volume 1, satisfies the critical point equation. In 1987 Besse proposed a conjecture that a solution of the critical point equation is Einstein. Since then, a number of mathematicians have given partial proof of the conjecture and obtained many geometric consequences. However, none has given a complete proof.
The purpose of the talk is to show that a compact 3-dimensional manifold M is isometric to the round 3-sphere $S^3$ if ker $s_g'* \not= 0$ and its second homology vanishes. Note that this Theorem implies that M is Einstein and hence that Conjecture holds on 3--dimensional compact manifold under certain topological conditions.
### 1/25 Jeffery Case, UCSB
``The Bakry-Emery tensor in Lorentzian geometry"

Abstract: In this talk, we will consider extensions of the Hawking-Penrose singularity theorems and the Lorentzian splitting theorem to the Bakry-Emery-Ricci tensor. We will point out similarities and differences to the setting in Riemannian geometry, and spend the most time on ideas less familiar in Riemannian geometry.
### 2/1 Colin Hinde, UCLA
``Synthetic Ricci Curvature and Optimal Transportation"

Abstract: We will review the solution of the optimal transportation problem on Riemannian manifolds. The investigation leads to a synthetic curvature condition equivalent to a lower bound on Ricci curvature yet requiring only the structure of a locally compact length space with a Borel measure. Yet, as in the case of Alexandrov Space, the synthetic curvature condition secures additional structure for free. We will discuss some results in this direction as well as localization of the condition, as time permits.
### 2/8, organization meeting

### 2/15, Rugang Ye, UCSB
``The entropy functional and the kappa-noncollapsing estimate for
the Ricci flow"

### 2/22, no meeting

### 2/29, Guofang Wei, UCSB
``An Introduction to Optimal Transportation"

### 3/7, Guofang Wei, UCSB
``Space of probability measures with Wasserstein distances"

# Differential Geometry Seminar Schedule for
Fall 2007

# Fridays 3:00 - 4:00pm, SH 6617

### 9/28, organization meeting

### 10/5 Rugang Ye, UCSB
``The Logarithmic Sobolev inequality along the Ricci flow"

### 10/12 Rugang Ye, UCSB
``The Logarithmic Sobolev inequality along the Ricci flow, continue"

### 10/19 Yujen Shu, UCSB
``Constant scalar curvature Kahler metrics on ruled surface"

Abstract: We will introduce the notion of constant scalar curvature Kahler
(cscK) metrics, and investigate the existence of such metrics on ruled
surfaces.
### 10/26 Zhenghan Wang, Microsoft/UCSB
``On Exotic (2+1)-TQFTs"

Abstract:
G. Moore and N. Seiberg conjectured in 1990s that every (2+1)-TQFT could be realized as
a Chern-Simons-Witten theory based on a pair (G,\lamda), where G is a compact (not necessarily connected)
Lie group, and \lambda a cohomology class in H^4(BG;Z). I will discuss examples of TQFTs constructed from Jones' subfactor theory which might not be realized in this way. This is a joint work with Seung-moon Hong of Indiana Univ and Eric Rowell of Texas A&M.
### 11/2 Zhongmin Shen, IUPUI
``Ricci curvature in Finsler geometry"

### 11/9 Rugang Ye, UCSB
``Analytic and geometric estimate for Ricci flow with surgeries"

### 11/16 Peter Petersen, UCLA
``Rigidity of shrinking Ricci solitons"

Abstract: I will survey several recent results on Ricci solitons. The goal is to find suitable conditions that make it possible to classify these objects. Several different conditions on curvature and symmetry allow us to classify these objetcs. Best of all in dimension 3 we can classify all shrinking solitions without further assumptions.
### 11/23 Thanksgiving

### 11/30 see Karen Vogtmann's talk

### 12/7 Andreas Malmendier, UCSB
``Rational elliptic surfaces and the u-plane integral"

Abstract: I will give a brief review of how the Seiberg-Witten families of elliptic curves with N_f=0,1,2,3,4 massive hypermultiplets define certain rational elliptic surfaces, p: Z -> CP^1, with non-stable singularities. I will then explain how the masses of the hypermultiplets are closely related to the homology of this surface: the root lattice T corresponding to the singularity type is embedded into H_2(Z). Oguiso and Shioda classified all possible structures for T and the Mordell-Weil group of p. Roughly, the evaluation of the holomorphic two-form on classes perpendicular to T then gives the masses of the hypermultiplets.
If time permits, I will explain how the Donaldson invariants for CP^2
can be computed by evaluating a certain ratio of functional determinants of a family of elliptic operators parametrized by the rational elliptic surface for N_f =0.
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