Ancient Solutions to Geometric Flows

Panagiota Daskalopoulos
Columbia University
May 20, 2019
Abstract: Some of the most important problems in geometric evolution partial differential equations are related to the understanding of singularities. This usually happens through a blow up procedure near the singularity which uses the scaling properties of the equation. In the case of a parabolic equation the blow up analysis often leads to special solutions which are defined for all time −∞ T≤+∞. We refer to them as ancient solutions. The classification of such solutions often sheds new insight upon the singularity analysis.

A probabilistic Takens theorem

Yonatan Gutman
Institute of Mathematics of the Polish Academy of Sciences
May 16, 2019
Let $X \subset \R^N$ be a Borel set, $\mu$ a Borel probability measure on $X$ and $T:X \to X$ a Lipschitz and injective map. Fix $k \in \N$ greater than the (Hausdorff) dimension of $X$ and assume that the set of $p$-periodic points has dimension smaller than $p$ for $p=1, \ldots, k-1$. We prove that for a typical polynomial perturbation $\tilde{h}$ of a given Lipschitz map $h : X \to \R$, the $k$-delay coordinate map $x \mapsto (\tilde{h}(x), \tilde{h}(Tx), \ldots, \tilde{h}(T^{k-1}x))$ is injective on a set of full measure $\mu$.

Two Important Milestones in the History of the Universe: The Last Scattering Surface, the Black Body Photosphere of the Universe and Distortions of the CMB Spectrum

Rashid Sunyaev
Distinguished Visiting Professor, School of Natural Sciences, IAS; Max-Planck-Institute für Astrophysik; Space Research Institute, Moscow
May 15, 2019

Our Universe is filled with Cosmic Microwave Background (CMB) radiation having an almost perfect black body spectrum with a temperature of To=2.7K. The number density of photons in our Universe exceeds the number density of electrons by a factor of more than a billion. In the expanding Universe the temperature at early times was higher than today: Tr = To (1+z), where z is the redshift. 

Singularity formation for some incompressible Euler flows

Tarek Elgindi
University of California, San Diego
May 6, 2019

We describe a recent construction of self-similar blow-up solutions of the incompressible Euler equation. A consequence of the construction is that there exist finite-energy $C^{1,a}$ solutions to the Euler equation which develop a singularity in finite time for some range of $a>0$. The approach we follow is to isolate a simple non-linear equation which encodes the leading order dynamics of solutions to the Euler equation in some regimes and then prove that the simple equation has stable self-similar blow-up solutions.

Singularities in reductions of Shimura varieties

Thomas Haines
University of Maryland
May 2, 2019

The singularities in the reduction modulo $p$ of the modular
curve $Y_0(p)$ are visualized by the famous picture of two curves
meeting transversally at the supersingular points. It is a fundamental
question to understand the singularities which arise in the reductions
modulo $p$ of integral models of Shimura varieties. For PEL type
Shimura varieties with parahoric level structure at $p$, this question
has been studied since the 1990's. Due to the recent construction of

Globally Consistent Three-family Standard Models in F-theory

Mirjam Cvetic
University of Pennsylvania
April 29, 2019

We present recent advances in constructions of globally consistent 
F-theory compactifications with the exact chiral spectrum of the minimal 
supersymmetric Standard Model. We highlight the first such example and 
then turn to a subsequent systematic exploration of the landscape of 
F-theory three-family Standard Models with a gauge coupling unification. 
Employing algebraic geometry techniques, all global consistency 
conditions of these models can be reduced to a single criterion on the