# Geometry & Analysis Seminar Fall 2017

McHenry Library Room 4130

For further information please contact Professor Francois Monard or call 831-459-2400

**Thursday,**October 5, 2017**No Seminar**

**Thursday,**October 12, 2017**Rohit Mishra, University of California, Santa Cruz**

**A Support Theorem for Integral Moments of a Symmetric****m****-Tensor Field**In this talk we give a brief account of a work done jointly with Anuj Abhishek, a graduate student at University of Tufts. We start with defining the

*q*-th integral moment,*I*, of any symmetric tensor field^{q }f*f*of order*m*over a simple, real-analytic Riemannian manifold of dimension*n*. The zeroth integral moment of such tensor fields coincides with the usual notion of geodesic ray transform of the tensor fields. Then we introduce some tools from geometry and microlocal analysis that we use to prove our result. Finally we give an outline of the proof for our main theorem which says that if we know*I*= 0 for^{q }f*q*= 0, 1, . . . ,*m*over the open set of geodesics not intersecting a geodesically convex set, then the support of*f*lies within that convex set.

**Thursday, October 19, 2017**

Jie Qing, University of California, Santa Cruz

Jie Qing, University of California, Santa Cruz

*Strong Rigidity for Asymptotically Hyperbolic Einstein Manifolds***I will introduce asymptotically hyperbolic Einstein manifolds and the impact to the study of conformal geometry. Then I will talk on our recent work on asymptotically hyperbolic Einstein manifolds based on the so-called AdS/CFT correspondence. I will present a proof for a sharp volume comparison theorem for asymptotically hyperbolic Einstein manifolds, which will imply not only the rigidity theorem for hyperbolic space in general dimension but also curvature estimates for asymptotically hyperbolic Einstein manifolds. In particular, as a consequence of our curvature estimates, one now knows that the asymptotically hyperbolic Einstein metrics with conformal infinities of sufficiently large Yamabe constant have to be negatively curved.**

**Thursday,**October 26, 2017

**I will present recent joint work showing that for any nondegenerate contact form on a closed three-manifold, the associated Reeb vector field has either two or infinitely many distinct embedded closed orbits as long as the associated contact structure has torsion Chern class. A key ingredient in the proof is an identity relating the lengths of certain sets of Reeb orbits to the volume of the three-manifold.**

**Daniel Cristofaro-Gardiner, University of California, Santa Cruz**

*Two or Infinity*

No Speaker

**Thursday, November 2, 2017**No Speaker

**The theory of harmonic map and its higher dimensional analogues (e.g. bi-harmonic map) has been a classic and intensely researched field in PDE and geometric analysis. In this talk, we will discuss an energy convexity for intrinsic bi-harmonic map and its heat flow with small intrinsic bi-energy from the 4-disc to spheres. This in particular yields the uniqueness of intrinsic bi-harmonic maps on the 4-disc with small bi-energy and the uniform convergence of the intrinsic bi-harmonic map heat flow on the 4-disc with small initial bi-energy. The energy convexity for harmonic maps with small energy was proved earlier by Colding-Minicozzi (c.f. Lamm-Lin) and the uniform convergence of the harmonic map heat flow with small initial energy was proved earlier by myself. This is a recent joint work with Paul Laurain.**

Longzhi Lin, University of California, Santa Cruz

**Thursday,**November 9, 2017Longzhi Lin, University of California, Santa Cruz

*Energy Convexity of Intrinsic Bi-harmonic Map and Its Heat Flow*

**Thursday,**November 16, 2017**Hanming Zhou, University of California, Santa Barbara**

**Lens rigidity for a particle in a Yang-Mills field**In this talk we consider the motion of a classical colored spinless particle under the influence of an external Yang-Mills potential $A$ on a compact manifold with boundary of dimension $\geq 3$. We show that under suitable convexity assumptions, we can recover the potential $A$, up to gauge transformations, from the lens data of the system, namely, scattering data plus travel times between boundary points. The talk is based on joint work with Gabriel Paternain and Gunther Uhlmann.

Holiday - No Seminar

**Thursday,**November 23, 2017Holiday - No Seminar

**PLEASE NOTE SPECIAL DAY**

Xinliang An,

**Wednesday, November 29**, 2017Xinliang An,

**University of Toronto**

*On Singularity Formation in General Relativity*In the process of gravitational collapse, singularities may form, which are either covered by trapped surfaces (black holes) or visible to faraway observers (naked singularities). In this talk, with three different approaches coming from hyperbolic PDE, quasilinear elliptic PDE and dynamical system, I will present results on four physical questions: i) Can “black holes” form dynamically in the vacuum? ii) To form a “black hole”, what is the least size of initial data? iii) Can we find the boundary of a “black hole” region? Can we show that a “black hole region” is emerging from a point? iv) For Einstein vacuum equations, could singularities other than black hole type form in gravitational collapse?

**Thursday, December 7, 2016****François Monard, University of California, Santa Cruz**

**Following the introductory talk I gave on 10/20/2017 at the Quantum Mechanics and Geometry Seminar earlier this quarter, on scattering and scattering poles, I will continue on introducing the main players of scattering problems, focusing on potential scattering on the real line. In the last talk, we proved the meromorphic continuation of the resolvent of 'Laplace + potential' across its continuous spectrum, and the existence of scattering poles, and we sketched their impact on long-term asymptotics of solutions to a wave equation.**

*Introduction to Scattering, Continued*Time permitting, this time I will cover:

- the absence of 'embedded eigenvalues' (=no eigenvalues inside the continuous spectrum)

- distorted plane waves and the generalization of the Fourier transform

- the scattering matrix and the wave operators

- inverse scattering