Bott-Chern cohomology is a refinement of de Rham cohomology on
complex manifolds. We shall discuss the limit of Bott-Chern cohomology in
terms of hypercohomology for semistable degeneration of complex manifolds.
As an application, we show that nonkahler Calabi-Yau 3-folds obtained by
conifold transition satisfy d d\bar lemma, hence admit a Hodge decomposition.
We describe a short, direct, alternative to the DeTurck trick to prove the
uniqueness of solutions to a large class of curvature flows of all orders,
including the Ricci flow, the L^2 curvature flow, and other flows related
to the ambient obstruction tensor. Our approach is based on the analysis
of simple energy quantities defined in terms of the actual solutions to the
equations, and allows one to avoid the step -- itself potentially
nontrivial in the noncompact setting -- of solving an auxiliary parabolic
equation (e.g., a k-harmonic-map heat-type flow) in order to overcome the
gauge-invariance-based degeneracy of the original flow. We also
demonstrate that, by the consideration of a certain energy
quotient/frequency-type quantity, one can give a short and quantitative
proof (avoiding Carleman inequalities) of the global backward uniqueness of
solutions to a large class of these equations.
Motivated by the pluriclosed flow of Streets and Tian, we establish
Evans-Krylov type estimates for parabolic "twisted" Monge-Ampere
equations in both the real and complex setting. In particular, a bound
on the second derivatives on solutions to these equations yields bounds
on Holder norms of the second derivatives. These equations are
parabolic but neither not convex nor concave, so the celebrated proof of
Evans-Krylov does not apply. In the real case, the method exploits a
partial Legendre transform to form second derivative quantities which
are subsolutions. Despite the lack of a bona fide complex Legendre
transform, we show the result holds in the complex case as well, by
formally aping the calculation. This is joint work with Jeff Streets.
Kapouleas and Yang have constructed, by gluing methods, sequences of
minimal embeddings in the round 3-sphere converging to the Clifford
torus counted with multiplicity 2. Each of their surfaces, which
they call doublings of the Clifford torus, resembles a pair of
coaxial tori connected by catenoidal tunnels and has symmetries
exchanging the two tori. I will describe an extension of their work
which yields doublings admitting no such symmetries as well as
examples incorporating an arbitrary (finite) number of tori, that
is Clifford torus triplings, quadruplings, and so on.
We prove that the expected value and median of the supremum of L^2 normalized random holomorphic fields of degree n on m-dimensional Kahler manifolds are asymptotically of order \sqrt{m\log n}.
There is an exponential concentration of measure of the sup norm around this median value. The estimates are based on the entropy methods of Dudley and Sudakov combined with a precise analysis of the relevant distance functions and covering numbers using off-diagonal asymptotics of Bergman kernels. This is the joint work with S. Zelditch.
From a complex analytic perspective Teichmüller space - the universal
cover of the moduli space of Riemann surfaces - is a contractible
bounded domain in a complex vector space. Likewise, Bounded Symmetric
domains arise as the universal covers of locally symmetric varieties
(of non-compact type). In this talk we will study isometric maps
between these two important classes of bounded domains equipped with
their intrinsic Kobayashi metric.
Based on the compactness of the moduli of non-collapsed Calabi-Yau
spaces with mild singularities, we set up a structure theory for
polarized K\"ahler Ricci flows with proper geometric bounds.
Our theory is a generalization of the structure theory
of non-collapsed K\"ahler Einstein manifolds.
As applications, we prove the Hamilton-Tian conjecture and the partial-
C0-conjecture of Tian. This is a joint work with Xiuxiong Chen.