Differential Geometry and Analysis Seminar
The seminar met
Wednesdays 2:30-3:30 at the Graduate Center
in room 5417 and was coorganized by Christina Sormani and David Fisher
of Lehman College.
Each talk was one hour long.
Schedule, Fall 2002
- Sept 18: Christina Sormani, Lehman College
"The Stability of Isotropy and Schur's Lemma"
Abstract: A Riemannian manifold is locally isotropic if locally the length of
a side of a triangle depends only on the lengths of the other two sides, their
common point,
and the angle between them. By Schur's Lemma such a manifold is a space
form (e.g. has constant sectional curvature). Here we will say that
a Riemannian
manifold is almost locally isotropic if locally the length of a side of
a triangle is close to a function $F$ of the lengths of the other two sides,
their base point and the angle between them.
We show that if compact manifold is sufficiently
almost isotropic depending on the minimum of its Ricci curvature
then it is Gromov-Hausdorff
close to a compact space form and the function $F$ is that of the space form.
- Sept 25: David Fisher, Lehman College
"Local Rigidity of Isometric Actions."
Click here for the abstract.
- Oct 2: Washek Pfeffer, University of California, Davis
hosted by: Dennis Sullivan/Mehrzad Ajoodanian
"Derivatives and Primatives"
Abstract: A very general Gauss-Green theorem can be obtained by differentiating
certain additive functions defined on the family of all bounded BV sets. The
process is invariant with respect to local lipeomorphisms, and the resulting
integration by parts formula can be used to study removable sets for PDEs
in divergence form. I plan to explain these results in an elementary
fashion, without assuming familiarity with BV sets and functions.
- Oct 9: Raphael Krikorian, Ecole Polytechnique, Paris
hosted by: David Fisher
"Positive Lyapunov exponents and differentiable rigidity of
linear quasi-periodic cocycles: non perturbative results"
Abstract: Let us consider linear quasi-periodic cocycles
which define the dynamics on R/Z x SL(2,R) which act as shifts
on the torus and smoothly on SL(2, R) by an action A.
The results are then the
following: If the action alpha on the torus is fixed and satisfies
a diophantine like property (full measure condition) then the
set of maps A for which
the fibered exponent of (alpha,A(.)) is positive, is dense in the
smooth topology.
- Oct 16: No meeting monday schedule
- Oct 23: Takayuki Yamauchi, DePauw University
hosted by: John Velling
"On the Construction of a Complete CMC Surface in the Hyperbolic
3-Space Determined by a Prescribed Hopf Differential"
Abstract: The role that a prescribed holomorphic Hopf differential A(z)dzdz
plays in the construction of a negatively curved immersed simply connected
complete surface S0 of prescribed constant mean curvature c \in (-1, 1) in
the hyperbolic 3-Space H3 is investigated in this work. When a holomorphic
function A(z), which is the coefficient function of the Hopf differential,
is prescribed on a unit disk |z| < 1, it is shown that the unit disk can be
immersed in the hyperbolic 3-Space H3 as a negatively curved complete
surface of constant mean curvature c \in (-1, 1), provided that |A(z)|
satisfies a certain growth condition. Moreover, it is shown that the unit
disk can be uniquely embedded in H3 when the holomorphic function A(z) has a
certain admissible structure.
- Oct 30: Bruno Klingler, Yale
hosted by: David Fisher
"On the Arithmeticity of Some Complex Hyperbolic Lattices"
Note the proof uses harmonic maps :) see the
abstract.
- Nov 6: Xiaochun Rong, Rutgers University at New Brunswick
hosted by: Christina Sormani
"A connectedness principle in the geometry of positive
curvature"
We develop a connectedness principle in the geometry of positive
curvature. In the form this is a surprising analog of the classical
connectedness principle in complex algebraic geometry.
The connectedness principle provides with not only a uniform formulation
for the classical Synge theorem, the Frankel theorem and a recent
theorem of Wilking, but also new connectedness theorems of positive
curvature.
- Nov 13: John Toth, McGill University
"Riemannian manifolds with uniformly bounded eigenfunctions."
Abstract: Let (M,g) be a compact, Riemannian manfold with Laplace-
Beltrami operator, \Delta. Assume that the L^{2}-normalized
Laplace eigenfunctions are all uniformly bounded. Does
this imply that (M,g) is a flat torus?
We discuss some recent joint work with Steve Zelditch
that answers this question in the affirmative when \Delta
is quantum completely integrable.
hosted by: David Fisher and Yiannis Petrides
- Nov 20: Mu Tao Wang, Columbia University
hosted by: David Fisher/Christina Sormani
"The Dirichlet
problem of the minimal surface system"
- Nov 27: Yiannis Petrides, Lehman College CUNY
"On the spectrum of Heisenberg manifolds.
Abstract: I will explain how methods from geometry (calculating the
geodesics), analysis (Guillemin-Duistermaat trace-formula) and analytic
number theory (Van der Corput's mathod on exponential sums and the method
of exponent pairs) can provide interesting results on the distribution of
eigenvalues of Heisenberg manifolds, in particular, on estimating the
error term in Weyl's Law.
- Dec 4: Penelope Smith, Lehigh University
"Perron's Method for Highly Nonlinear Second Order Hyperbolic Equations"