Equivariant eta forms and differential K theory

Speaker: 

Bo Liu

Institution: 

UC Santa Barbara

Time: 

Tuesday, June 6, 2017 - 4:00pm to 5:00pm

Location: 

RH 306

The eta form of Bismut–Cheeger is the higher degree version of the Atiyah-Patodi-Singer eta invariant, i.e. it is exactly the boundary correction term in the family index theorem for manifolds with boundary. In this talk, I'll study the properties of eta forms and extend them to the equivariant version for compact Lie group action. Moreover, the applications of eta forms in differential K theory will be discussed.

Free boundary minimal hypersurfaces

Speaker: 

Lucas Ambrozio

Institution: 

University of Chicago

Time: 

Tuesday, June 13, 2017 - 4:00pm to 5:00pm

Location: 

RH 340P

We will review some recent work on free boundary minimal
hypersurfaces. In particular, we will explain a geometric classification
of the critical catenoid (joint with Ivaldo Nunes) and discuss what
information about such hypersurfaces in a general ambient manifold one can
extract from the knowledge of their Morse index (joint with Alessandro
Carlotto and Ben Sharp).

Connecting the Kontsevich-Witten and Hodge tau-functions by the Virasoro operators

Speaker: 

Xiaobo Liu

Institution: 

Peking Univ. and Notre Dame University

Time: 

Tuesday, May 2, 2017 - 4:00pm to 5:00pm

Location: 

RH 306

Kontsevich-Witten tau-function and the Hodge tau-function
are generating functions for two types of intersection numbers on
moduli spaces of stable curves. Both of them are tau functions for the
KP hierarchy. In this talk, I will describe how to connect these two
tau-functions by differential operators belonging to the
$\widehat{GL(\infty)}$ group. Indeed, these two tau-functions can be
connected using Virasoro operators. This proves a conjecture posted by
Alexandrov. This is a joint work with Gehao Wang.

Limits of Yang-Mills α-connections

Speaker: 

Casey Kelleher

Institution: 

UC Irvine

Time: 

Tuesday, March 21, 2017 - 4:00pm

Location: 

RH 306

In the spirit of recent work of Lamm, Malchiodi and Micallef in the setting of harmonic maps, we identify Yang-Mills connections obtained by approximations with respect to the Yang-Mills α- energy. More specifically, we show that for the SU(2) Hopf fibration over S4, for sufficiently small α values the SO(5, 1)-invariant ADHM instanton is the unique α-critical point which has Yang-Mills α-energy lower than a specific threshold. 

Symplectic Laplacians, boundary conditions and cohomology

Speaker: 

Lihan Wang

Institution: 

UC Riverside

Time: 

Tuesday, May 9, 2017 - 4:00pm

Location: 

RH 306

In 2012, Tseng and Yau introduced several Laplacians on symplectic manifolds that are related to a system of supersymmetric equations from physics.  In this talk, we will discuss these "symplectic Laplacians" and their relations with cohomologies on compact symplectic manifolds with boundary.  For this purpose, we will introduce new boundary conditions for differential forms on symplectic manifolds.  Their properties and importance will be discussed.

Joint UCI-UCR-UCSD Southern California Differential Geometry Seminar

Institution: 

SCDGS

Time: 

Friday, April 21, 2017 - 3:00pm to 5:00pm

Location: 

UC Riverside Surge 284

Program:

3:10 - 4:00 PM    Pengzi Miao (Univ. of Miami)

4:10 - 5:00 PM    Jonathan Luk (Stanford Univ.)

 

Title/Abstract:

 

Pengzi Miao (University of Miami)

Title:  Minimal hypersurfaces and boundary behavior of compact manifolds with
nonnegative scalar curvature

Abstract:
On a compact Riemannian manifold with boundary having positive mean
curvature, a fundamental result of Shi and Tam states that, if the
manifold has nonnegative scalar curvature and if the boundary is
isometric to a strictly convex hypersurface in the Euclidean space,
then the total mean curvature of the boundary is no greater than the
total mean curvature of the corresponding Euclidean hypersurface. In
3-dimension, Shi-Tam's result is known to be equivalent to the
Riemannian positive mass theorem.

In this talk, we will discuss a supplement to Shi-Tam's theorem
by including the effect of minimal hypersurfaces on a chosen boundary
component. More precisely, we consider a compact manifold with
nonnegative scalar curvature, whose boundary consists of two parts,
the outer boundary and the horizon boundary. Here the horizon
boundary is the union of all closed minimal hypersurfaces in the
manifold and the outer boundary is assumed to be a topological
sphere. In a relativistic context, such a manifold represents a body
surrounding apparent horizon of black holes in a time symmetric
initial data set. By assuming the outer boundary is isometric to a
suitable 2-convex hypersurface in a Schwarzschild manifold of
positive mass m, we establish an inequality relating m, the area of
the horizon boundary, and two weighted total mean curvatures of the
outer boundary and the hypersurface in the Schwarzschild manifold. In
3-dimension, our result is equivalent to the Riemannian Penrose
inequality. This is joint work with Siyuan Lu.

 

Jonathan Luk (Stanford University)

Title: Strong cosmic censorship in spherical symmetry for two-ended
asymptotically flat data

Abstract:
I will present a recent work (joint with Sung-Jin Oh) on the strong
cosmic censorship conjecture for the
Einstein-Maxwell-(real)-scalar-field system in spherical symmetry for
two-ended asymptotically flat data. For this model, it was previously
proved (by M. Dafermos and I. Rodnianski) that a certain formulation
of the strong cosmic censorship conjecture is false, namely, the
maximal globally hyperbolic development of a data set in this class
is extendible as a Lorentzian manifold with a C0 metric. Our main
result is that, nevertheless, a weaker formulation of the conjecture
is true for this model, i.e., for a generic (possibly large) data set
in this class, the maximal globally hyperbolic development is
inextendible as a Lorentzian manifold with a C2 metric.

 

The Dirichlet problem for the Lagrangian phase operator

Speaker: 

Sebastien Picard

Institution: 

Columbia University

Time: 

Tuesday, May 23, 2017 - 4:00pm to 5:00pm

Location: 

RH 306

The Lagrangian phase operator arises in the study of calibrated geometries and the deformed Hermitian-Yang-Mills equation in complex geometry. We study a local version of these geometric problems, and solve the Dirichlet problem for the Lagrangian phase operator with supercritical phase given the existence of a subsolution. They key step is to find hidden concavity properties in order to obtain a priori estimates. This is joint work with T. Collins and X. Wu.

Fundamental gap for convex domains of the sphere

Speaker: 

Shoo Seto

Institution: 

UCSB

Time: 

Monday, February 6, 2017 - 4:00pm to 5:00pm

Host: 

Location: 

340N Rowland Hall

In this talk, we introduce the Laplacian eigenvalue problem and briefly go over its history.  Then we will present a recent result which gives a sharp lower bound of the fundamental gap for convex domain of spheres motivated by the modulus of continuity approach introduced by Andrews-Clutterbuck.  This is joint work with Lili Wang and Guofang Wei.

Holomorphic Twistor Spaces and Bihermitian Geometry

Speaker: 

Steve Gindi

Institution: 

UC Riverside

Time: 

Tuesday, May 16, 2017 - 4:00pm

Location: 

RH 306

Ever since the 1970's, holomorphic twistor spaces have been used to study the geometry and analysis of their base manifolds. In this talk, we will introduce integrable complex structures on twistor spaces fibered over complex manifolds that are equipped with certain geometrical data. The importance of these spaces will be shown to lie, for instance, in their applications to bihermitian geometry, also known as generalized Kahler geometry. (This is part of the generalized geometry program initiated by Nigel Hitchin.) By analyzing their twistor spaces, we will develop a new approach to studying bihermitian manifolds. In fact, we will demonstrate that the twistor space of a bihermitian manifold is equipped with two complex structures and natural holomorphic sections as well. This will allow us to construct tools from the twistor space that will lead, in particular, to new insights into the real and holomorphic Poisson structures on the manifold. 

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