Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2024 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Ruobing Zhang)

  • Nov. 22, 2024, Friday, 2:30-3:30pm, Fine Hall 214, Princeton University

    Speaker: Aaron Naber, Institute for Advanced Study

    Title: The Energy Identity for Nonlinear Harmonic Maps

    Abstract: We begin this talk with an introduction to linear and nonlinear harmonic maps between Riemannian manifolds, with a first goal of understanding some basic examples and uses in geometry and analysis. Unlike linear harmonic maps, which are always smooth and well behaved, nonlinear harmonic maps may exhibit singularities of various sorts. One type of singularity which appears is in the form of discontinuous points of a fixed solution. Another singularity type which appears is in the form of blow up for a sequences of solutions. The singularities which can form for such a sequences of solutions should not be arbitrary, but have conjecturally obeyed the so called Energy Identity. I will discuss recent joint work with Daniele Valtorta which resolved this problem.

  • Nov. 22, 2024, Friday, 4:00-5:00pm, Fine Hall 214, Princeton University

    Speaker: Alessio Figalli, Institute for Advanced Study & ETH

    Title: The De Giorgi Conjecture for the Free Boundary Allen-Cahn Equation

    Abstract: The Allen-Cahn (AC) equation is known to approximate minimal surfaces, leading to the conjecture that global stable solutions to AC should be one-dimensional in dimensions up to 7. If true, this result would imply the celebrated De Giorgi conjecture for monotone solutions. Recognizing the interactive nature of the AC equation, Jerison has advocated for more than a decade that a free-boundary version of AC would offer a more natural framework for approximating minimal surfaces. This perspective motivates studying the above conjecture within this free-boundary context. In recent joint work with Chan, Fernandez-Real, and Serra, we classify all stable global solutions to the one-phase Bernoulli free-boundary problem in three dimensions and, as a consequence, we establish that global stable 3d solutions to the free-boundary AC equation are one-dimensional.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2024 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Ruobing Zhang)

  • March 29, 2024, Friday, 2:00-3:00pm, Room 208, Science & Engineering Resource Center (SEC 208), Busch Campus, Rutgers University

    Speaker: Aleksandr Logunov, MIT

    Title: Fastest rate of localization for eigenfunctions

    Abstract: The Laplace operator in the Euclidean space has no L^2 eigenfunctions, but by perturbing the metric or adding a potential one can construct a plenty of examples of operators with L^2 integrable eigenfunctions. Landis conjecture states that any non-zero solution to \Delta u + V u=0 in the Euclidean space with real bounded V cannot decay faster than exponentially near infinity. If we are allowed to slightly perturb the coefficients of the Laplace operator (for instance taking a small smooth perturbation of the Euclidean metric and taking the Laplace operator for this metric ) how fast can we force an eigenfunction of the perturbed Laplace operator to be localized? We will review known results, related open questions and recent constructions of Nazarov and AL, Filonov and Krymskii, Pagano, AL and Krymskii of eigenfunctions to linear elliptic operators with smooth coefficients, which are localized much faster than exponentially.

  • March 29, 2024, Friday, 3:30-4:30pm, Room 208, Science & Engineering Resource Center (SEC 208), Busch Campus, Rutgers University

    Speaker: Tristan Ozuch, MIT

    Title: Orbifold singularity formation along ancient and immortal Ricci flows

    Abstract: Dimension $4$ is the next horizon for applications of Ricci flow to topology, where the main goal is to understand the topological operations that Ricci flow performs both at singular times, and in its long-term behavior. With Alix Deruelle, we explain how Ricci flow develops or resolves orbifold singularities by a notion of stability for orbifold Ricci solitons that we introduce depending only on the curvature at the singular points. We construct ancient and immortal Ricci flows spontaneously forming or desingularizing arbitrarily complicated orbifold singularities by bubbling-off Ricci-flat ALE metrics. This unexpectedly predicts that singular spherical and cylindrical orbifolds should not appear as finite-time singularity models. On the other hand, (complex) hyperbolic orbifolds appear as limits of immortal "thick" $4$-dimensional Ricci flows as $t\to+\infty$.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2023 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Ruobing Zhang)

  • Nov. 17, 2023, Friday, 2:00-3:00pm, McDonnell A01, Princeton University

    Speaker: Ovidiu Savin, Columbia University

    Title: Non C^1 solutions to the special Lagrangian equation

    Abstract: We discuss the existence of viscosity solutions to the special Lagrangian equation that are Lipschitz but not C^1, and have non-minimal gradient graphs. This is a joint work with C. Mooney.

  • Nov. 17, 2023, Friday, 3:30-4:30pm, McDonnell A01, Princeton University

    Speaker: Ana Menezes, Princeton University

    Title: Eigenvalue problems and free boundary minimal surfaces in spherical caps

    Abstract: In a recent work with Vanderson Lima (UFRGS, Brazil), we introduced a family of functionals on the space of Riemannian metrics of a compact surface with boundary, defined via eigenvalues of a Steklov-type problem. In this talk we will prove that each such functional is uniformly bounded from above, and we will characterize maximizing metrics as induced by free boundary minimal immersions in some geodesic ball of a round sphere. Also, we will determine that the maximizer in the case of a disk is a spherical cap of dimension two, and we will prove rotational symmetry of free boundary minimal annuli in geodesic balls of round spheres which are immersed by first eigenfunctions.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2023 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Ruobing Zhang)

  • April 21, 2023, Friday, 2:00-3:00pm, Room 208, Science & Engineering Resource Center (SEC 208), Busch Campus, Rutgers University

    Speaker: Qing Han, University of Notre Dame

    Title: Asymptotic analysis for harmonic maps with prescribed singularities

    Abstract: Motivated by studies of axially symmetric stationary solutions of the Einstein vacuum equations in general relativity, we study singular harmonic maps from the 3-dimensional Euclidean space to the hyperbolic plane, with prescribed singularities. We prove that every such harmonic map has a unique tangent map at the black hole horizon and the harmonic map depends on the location of the black hole smoothly. The collection of parameters representing the conical singularities in the tangent map determines a flow along which the reduced energy of the harmonic map is decreasing. The harmonic map equation restricted to the unit sphere has a singularity at the north and south poles. The talk is based on joint work with Marcus Khuri, Gilbert Weinstein, and Jingang Xiong.

  • April 21, 2023, Friday, 3:30-4:30pm, Room 208, Science & Engineering Resource Center (SEC 208), Busch Campus, Rutgers University

    Speaker: Ruobing Zhang, Princeton University

    Title: Metric geometry of collapsing Einstein 4-manifolds: recent progress and open questions

    Abstract: The studies of degenerating Einstein manifolds have been very active during the past three decades. Compared with rather complete understandings in the volume non-collapsing case, due to substantial challenges and fundamental difficulties, the geometry of collapsing Einstein manifolds is much less explored while its applications are being widely demanded in different disciplines of geometry and physics. Intensive investigations focus on the collapsing Einstein 4-manifolds with special holonomy in the recent years. This talk will exhibit major progress by different research groups in the field, which can be regarded as an important step towards the direction of studying the general case. We will also propose open questions (some of them are folklore).

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2022 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Ruobing Zhang)

  • December 9, 2022, Friday, 2:30-3:30pm, Fine Hall 110, Princeton University

    Speaker: Valentino Tosatti, Courant Institute, NYU

    Title: Collapsing Ricci-flat metrics: estimates or no estimates?

    Abstract: Compact Calabi-Yau manifolds admit Ricci-flat Kahler metrics thanks to a celebrated theorem of Yau, a unique such metric in each Kahler cohomology class. If we degenerate the class, the corresponding Ricci-flat metrics will also degenerate, and one can ask whether they admit uniform bounds (in all C^k norms) away from a closed analytic subvariety. This is known when the metrics are not collapsing, but the collapsing case is much more challenging. I will discuss how the answer to this question is positive when the limiting class comes from the base of a fibration (joint with Hein), and negative in general when there is no such fibration (joint with Filip), and raise some related open questions.

  • December 9, 2022, Friday, 4:00-5:00pm, Fine Hall 110, Princeton University

    Speaker: Yang Li, Massachusetts Institute of Technology

    Title: Metric SYZ conjecture

    Abstract: The Strominger-Yau-Zaslow conjecture asks to find a special Lagrangian torus fibration on a Calabi-Yau manifold sufficiently close to the large complex structure limit. The conjecture sits at the crossroad of algebraic, symplectic, Riemannian geometry, and mirror symmetry. We will focus on the metric aspects, and primarily on the case of the Fermat family, where one can show the existence of the SYZ fibration in the generic region, namely an open subset of the manifold containing most of the measure.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2022 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Ruobing Zhang)

  • April 15, 2022, Friday, 2:00 - 3:00pm (EST), Zoom link: (https://princeton.zoom.us/j/92668943856) (Meeting ID: 926 6894 3856)

    Speaker: Richard Bamler, University of California, Berkeley

    Title: Towards a theory of Ricci flow in dimension 4 (and higher)

    Abstract: The Ricci flow (with surgery) has proven to be a powerful tool in the study of 3-dimensional topology — its most prominent application being the verification of the Poincaré and Geometrization Conjectures by Perelman about 20 years ago. Since then further research has led to a satisfactory understanding of the flow and surgery process in dimension 3. In dimensions 4 and higher, on the other hand, Ricci flows have been understood relatively poorly and a surgery construction seemed distant. Recently, however, there has been some progress in the form of a new compactness and partial regularity theory for higher dimensional Ricci flows. This theory relies on a new geometric perspective on Ricci flows and provides a better understanding of the singularity formation and long-time behavior of the flow. In dimension 4, in particular, it may eventually open up the possibility of a surgery construction or a construction of a "flow through singularities". The goal of this talk will be to describe this new compactness and partial regularity theory and the new geometric intuition that lies behind it. Next, I will focus on 4-dimensional flows. I will present applications towards the study of singularities of such flows and discuss several conjectures that provide a possible picture of a surgery construction in dimension 4. Lastly, I will discuss potential topological applications.

  • April 15, 2022, Friday, 3:00-3:30pm (EST), Coffee Hour: (https://app.gather.town/app/GnWiTsGZ9m8b77Sb/Joint%20seminar%202022)

  • April 15, 2022, Friday, 3:30 - 4:30pm (EST), Zoom link: (https://princeton.zoom.us/j/92668943856) (Meeting ID: 926 6894 3856)

    Speaker: Ovidiu Munteanu, University of Connecticut

    Title: Comparison results for complete noncompact three-dimensional manifolds

    Abstract: Typical comparison results in Riemannian geometry, such as for volume or for spectrum of the Laplacian, require Ricci curvature lower bounds. In dimension three, we can prove some related sharp comparison estimates assuming only a scalar curvature bound. The talk will present these results, their applications, and explain how dimension three is used in the proofs.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2021 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song;Organizers on Princeton side: Sun-Yung Alice Chang and Ruobing Zhang )

  • December 10, 2021, Friday, 1:00pm (EST), Zoom link: (https://princeton.zoom.us/j/92668943856) (Meeting ID: 926 6894 3856)

    Speaker: Juncheng Wei, The University of British Columbia

    Title: Stability of Sobolev and Harmonic Map Inequalities

    Abstract: In this talk, I will discuss our recent results on stability of Sobolev inequalities and Harmonic Map Inequalities. For Sobolev inequality we obtain the sharp estimates of the deficiency of $u$ and sum of Talenti bubbles in terms of the $H^{-1}$ norm of the Yamabe equation $\Delta u + u^{\frac{n+2}{n-2}}$. For Harmonic Maps Inequalities, we show that a striking dichotomy in stability between degree one and higher degree maps. (Joint work with B. Deng and L. Sun.)

  • December 10, 2021, Friday, 2:00-2:30pm (EST), Coffee Hour: (https://gather.town/invite?token=TQlTdtInLUCwYQUwdKXaIvJGQ7Y2wPcV) (Password: PR122021)

  • December 10, 2021, Friday, 2:30pm (EST), Zoom link: (https://princeton.zoom.us/j/92668943856) (Meeting ID: 926 6894 3856)

    Speaker: Eden Prywes, Princeton University

    Title: Quasiconformal and Quasiregular Maps in Dimensions Larger than Two

    Abstract: A quasiconformal map on n-dimensional Euclidean space is a homeomorphism whose differential has bounded distortion at almost every point. I will discuss these maps and their non-homeomorphic counterparts, quasiregular maps. I will give a historical background and discuss their properties. I will then present some recent work regarding their relation to bilipschitz maps and also their generalizations, quasiregular curves.

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    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2021 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Chao Li )

  • May 24, 2021, Monday, 12:30pm, Coffee Hour: (https://gather.town/app/Ybqg2gluvOoZuIvq/JointSeminar)

  • May 24, 2021, Monday, 1:00pm, Zoom Meeting ( https://princeton.zoom.us/j/95636729444)

    Speaker: Nick Edelen, University of Notre Dame

    Title: Degeneration of 7-dimensional minimal hypersurfaces which are stable or have bounded index

    Abstract: A 7-dimensional area-minimizing hypersurface $M$ can have in general a discrete singular set. The same is true if M is only locally-stable for the area-functional, provided $\haus^6(sing M) = 0$. In this paper we show that if $M_i$ is a sequence of 7D minimal hypersurfaces with discrete singular set which are minimizing, stable, or have bounded index, and varifold-converge to some $M$, then the geometry, topology, and singular set of the $M_i$ can degenerate in only a very precise manner. We show that one can always ``parameterize'' a subsequence $i'$ by ambient, controlled bi-Lipschitz maps taking $\phi_{i'}(M_1) = M_{i'}$. As a consequence, we prove that the space of closed, $C^2$ embedded minimal hypersurfaces in a closed 8-manifold $(N, g)$ with a priori bounds $\haus^7(M) \leq \Lambda$ and $index(M) \leq I$ divides into finitely-many diffeomorphism types, and this finiteness continues to hold if one allows the metric $g$ to vary, or $M$ to be singular.

  • May 24, 2021, Monday, 2:15pm, Zoom Meeting ( https://princeton.zoom.us/j/95636729444)

    Speaker: Dennis Kriventsov, Rutgers University

    Title: Stability for Faber-Krahn inequalities and the ACF formula

    Abstract: The Faber-Krahn inequality states that the first Dirichlet eigenvalue of the Laplacian on a domain is greater than or equal to that of a ball of the same volume (and if equality holds, then the domain is a translate of a ball). Similar inequalities are available on other manifolds where balls minimize perimeter over sets of a given volume. I will discuss the stability problem for such inequalities: if the eigenvalue of a set is close to a ball, how similar to a ball must the set look like? I will also explain an application of sufficiently strong stability results to quantifying the behavior of the Alt-Caffarelli-Friedman monotonicity formula, which has implications for free boundary problems with multiple phases. This is based on recent joint work with Mark Allen and Robin Neumayer.

  • May 24, 2021, Monday, 3:30pm, Coffee Hour: (https://gather.town/app/Ybqg2gluvOoZuIvq/JointSeminar)

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2020 (Organizers on Rutgers side:Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song;Organizers on Princeton side: Sun-Yung Alice Chang and Chao Li )

  • Nov. 13, 2020, Friday, 1:00pm, Coffee Hour: https://gather.town/app/Ybqg2gluvOoZuIvq/JointSeminar

  • Nov. 13, 2020, Friday, 1:30pm, Zoom Meeting https://princeton.zoom.us/j/99986635712

    Speaker: Jingrui Cheng, The State University of New York at Stony Brook

    Title: Constant scalar curvature Kahler metrics and properness theorem

    Abstract: Constant scalar curvature Kahler metric(cscK) is a natural higher dimensional generalization of the constant curvature metric on Riemann surfaces. One of the main difficulties in understanding the existence of cscK metric is the complexity of the underlying partial differential equation. We take up this challenge and show that the existence of cscK metric on compact Kahler manifold is equivalent to the properness of Mabuchi energy (whose critical point are cscK metrics). I will also discuss future problems if time permits. This is based on joint work with Xiuxiong Chen.

  • Nov. 13, 2020, Friday, 2:45pm, Zoom Meeting https://princeton.zoom.us/j/99986635712

    Speaker: Mat Langford University of Tennessee at Knoxville

    Title: The atomic structure of ancient grain boundaries

    Abstract: I will present a series of far-reaching new existence and structure results for convex ancient solutions to mean curvature flow. An interesting picture (conjectured by Huisken and Sinestrari) emerges: convex ancient and translating solutions in slab regions decompose into certain canonical configurations of Grim Reapers, subject to certain necessary constraints. In particular, we construct new families of solutions with discrete symmetries as well as families of solutions which possess only a single reflection symmetry. These include many eternal solutions which do not evolve by translation (resolving a conjecture of White in the negative). Prior to these results, the only known examples were the rotationally symmetric ancient pancake and the rotationally symmetric flying wing translators. Several interesting questions remain open, however. This is joint work with Theodora Bourni and Giuseppe Tinaglia.

  • Nov. 13, 2020, Friday, 3:45pm, Coffee Hour: https://gather.town/app/Ybqg2gluvOoZuIvq/JointSeminar

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2019 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizers on Princeton side: Sun-Yung Alice Chang and Chao Li)

  • October 16, 2019, Wed., 1:45-2:45pm, Jadwin Hall A08, Princeton University

    Speaker: Yannick Sire, Johns Hopkins University

    Title: New result on constant Q-curvature metrics

    Abstract: In the recent years, several major results have been obtained in the problem of finding a constant Q-curvature metric in a given conformal class in dimensions bigger than 5. This talk will cover new results concerning existence and multiplicity of such metrics. I will first present a rather general geometric approach to prove existence and multiplicity of regular metrics, giving several explicit examples. Then I will move to the case of singular metrics, i.e. complete metrics with constant Q-curvature outside of a closed set. This requires to develop several tools to handle 4th order equations (but applicable actually to higher order ones). I will also provide some explicit examples of such metrics and investigate their multiplicity. I will state open problems as well.

  • October 16, 2019, Wed., 3-4pm, Fine Hall 314, Princeton University

    Speaker: Bruce Kleiner, Courant Institute

    Title: Ricci flow and contractibility of spaces of metrics

    Abstract: In the lecture I will discuss recent joint work with Richard Bamler, which uses Ricci flow through singularities to construct deformations of spaces of metrics on 3-manifolds. We show that the space of metrics with positive scalar on any 3-manifold is either contractible or empty; this extends earlier work by Fernando Marques, which proved path-connectedness. We also show that for any spherical space form M, the space of metrics with constant sectional curvature is contractible. This completes the proof of the Generalized Smale Conjecture, and gives a new proof of the original Smale Conjecture for S^3.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2018 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizer on Princeton side: Alice Chang)

  • April 17, 2018, Tuesday, 1:40pm, Hill 705, Rutgers University

    Speaker: Jiaping Wang, University of Minnesota

    Title: Green's function estimates and applications

    Abstract: We plan to discuss an L^1 estimate for the Green's function on manifolds with positive bottom spectrum. As an application, we derive a curvature decay estimate for a class of steady Ricci solitons. This is a joint work with Ovidiu Munteanu and Chiung-Jue Sung.

  • April 17, 2018, 3:00pm, Hill 705, Rutgers University

    Speaker: Fang Wang, Shanghai Jiao Tong University

    Title: Obata type rigidity theorems on manifold with boundary and their applications

    Abstract: In this talk, I will introduce some rigidity theorems for the (generalized) Obata equation on manifolds with boundary with different kinds of boundary conditions. Then I will also give two main applications. One application is in the rigidity theorems of Poincare-Einstein manifolds; and the other is in the first eigenvalue problems on manifolds with boundary. This is joint work with Mijia Lai and Xuezhang Chen.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2017 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizer on Princeton side: Alice Chang )

  • November 20, 2017, 2:00pm, Fine 224, Princeton University

    Speaker: Paul Yang, Princeton University

    Title: CR invariant area functionals and the singular CR Yamabe solutions on the Heisenberg of $H^{1}$

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2017 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizer on Princeton side: Alice Chang)

  • April 18, 2017, 1:40pm, Hill 705, Rutgers University

    Speaker: Philip Isett, MIT

    Title: A Proof of Onsager's Conjecture for the Incompressible Euler Equations

    Abstract: In an effort to explain how anomalous dissipation of energy occurs in hydrodynamic turbulence, Onsager conjectured in 1949 that weak solutions to the incompressible Euler equations may fail to exhibit conservation of energy if their spatial regularity is below 1/3-Holder. I will discuss a proof of this conjecture that shows that there are nonzero, (1/3-\epsilon)-Holder Euler flows in 3D that have compact support in time. The construction is based on a method known as "convex integration," which has its origins in the work of Nash on isometric embeddings with low codimension and low regularity. A version of this method was first developed for the incompressible Euler equations by De Lellis and Szekelyhidi to build Holder-continuous Euler flows that fail to conserve energy, and was later improved by Isett and by Buckmaster-De Lellis-Szekelyhidi to obtain further partial results towards Onsager's conjecture. The proof of the full conjecture combines convex integration using the "Mikado flows" introduced by Daneri-Szekelyhidi with a new "gluing approximation" technique. The latter technique exploits a special structure in the linearization of the incompressible Euler equations.

  • April 18, 2017, 3:00pm, Hill 705, Rutgers University

    Speaker: Matthew J. Gursky, University of Notre Dame

    Title: Some existence and non-existence results for Poincare-Einstein metrics

    Abstract: I will begin with a brief overview of the existence question for conformally compact Einstein manifolds with prescribed conformal infinity. After stating the seminal result of Graham-Lee, I will discuss a non-existence result (joint with Qing Han) for certain conformal classes on the 7-dimensional sphere. I will also mention some ongoing work (with Gabor Szekelyhidi) on a version of "local existence" of Poincare-Einstein metrics.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2016 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizer on Princeton side: Alice Chang)

  • October 21, 2016, 2:00pm, Princeton - Fine Hall 224

    Speaker: Yanyan Li, Rutgers University

    Title: Blow up analysis of solutions of conformally invariant fully nonlinear elliptic equations

    Abstract: We establish blow-up profiles for any blowing-up sequence of solutions of genera l conformally invariant fully nonlinear elliptic equations on Euclidean domains. We prove that (i) the distance between blow-up points is bounded from below by a universal positive number, (ii) the solutions are very close to a single stand ard bubble in a universal positive distance around each blow-up point, and (iii) the heights of these bubbles are comparable by a universal factor. As an applic ation of this result, we establish a quantitative Liouville theorem. This is a joint work with Luc Nguyen.

  • October 21, 2016, 3:30pm, Princeton - Fine Hall 224

    Speaker: Yi Wang, Johns Hopkins University

    Title: A fully nonlinear Sobolev trace inequality

    Abstract: The $k$-Hessian operator $sigma_k$ is the $k$-th elementary symmetric function of the eigenvalues of the Hessian. It is known that the $k$-Hessian equation $sigma_k(D^2 u)=f$ with Dirichlet boundary condition $u=0$ is variational; indeed, this problem can be studied by means of the $k$-Hessian energy $int -u sigma_k(D^2 u)$. We construct a natural boundary functional which, when added to the $k$-Hessian energy, yields as its critical points solutions of $k$-Hessian equations with general non-vanishing boundary data. As a consequence, we prove a sharp Sobolev trace inequality for $k$-admissible functions $u$ which estimates the $k$-Hessian energy in terms of the boundary values of $u$. This is joint work with Jeffrey Case.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2016 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizer on Princeton side: Alice Chang)

  • April 5, 2016, 4:00pm Hill 705

    Speaker: Changfeng Gui, University of Connecticut

    Title: Moser-Trudinger type inequalities, mean field equations and Onsager vortices

    Abstract: In this talk, I will present a recent work confirming the best constant of a Moser-Trudinger type inequality conjectured by A. Chang and P. Yang. The proof is based on a new and powerful lower bound of total mass for mean field equations. Other applications of the lower bound include the classification of certain Onsager vortices on the sphere, the radially symmetry of solutions to Gaussian curvature equation on the plane, classification of solutions for mean field equations on tori and the sphere, etc. The resolution of several interesting problems in these areas will be presented. The work is jointly done with Amir Moradifam from UC Riverside.

  • April 5, 2016, 5:15pm, Hill 705

    Speaker: Jacob Bernstein, Johns Hopkins University

    Title: Hypersurfaces of low entropy

    Abstract: The entropy is a natural geometric quantity introduced by Colding and Minicozzi and may be thought of as a rough measure of the complexity of a hypersurface of Euclidean space. It is closely related to the mean curvature flow. On the one hand, the entropy controls what types of singularities the flow develops. On the other, the flow may be used to study the entropy. In this talk I will survey some recent results with Lu Wang that show that hypersurfaces of low entropy can't be too complicated.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2015 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Organizer on Princeton side: Alice Chang)

  • Oct. 16, 2015, Friday, 3:00pm, Fine Hall 314, Princeton University

    Speaker: Andrea Malchiodi, Scuola Normale Superiore

    Title: Embedded Willmore tori in three-manifolds with small area constraint

    Abstract: While there are lots of contributions on Willmore surfaces in the three-dimensional Euclidean space, the literature on curved manifolds is still relatively limited. One of the main aspects of the Willmore problem is the loss of compactness under conformal transformations. We construct embedded Willmore tori in manifolds with a small area constraint by analyzing how the Willmore energy under the action of the Mobius group is affected by the curvature of the ambient manifold. The loss of compactness is then taken care of using minimization arguments or Morse theory.

  • Oct. 16, 2015, Friday, 4:15pm, Fine Hall 314, Princeton University

    Speaker: Daniela De Silva, Columbia University

    Title: The two membranes problem

    Abstract: We will consider the two membranes obstacle problem for two different operators, possibly non-local. In the case when the two operators have different orders, we discuss how to obtain $C^{1,\gamma}$ regularity of the solutions. In particular, for two fractional Laplacians of different orders, one obtains optimal regularity and a characterization of the boundary of the coincidence set. This is a joint work with L. Caffarellii and O. Savin.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2015 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Antonio Ache)

  • May 5, 2015, Tuesday, 4:00pm, Hill 705, Rutgers University

    Speaker: Gregory Seregin, The University of Oxford

    Title: Ancient solutions to Navier-Stokes equations

    Abstract: In the talk, I shall try to explain the relationship between the so-called ancient (backwards) solutions to the Navier-Stokes equations in the space or in a half space and the global well-posedness of initial boundary value problems for these equations. Ancient solutions itself are an interesting part of the the theory of PDE's. Among important questions to ask are classification, smoothness, existence of non-trivial solutions, etc. The latter problem is in fact a Liouville type theory for non-stationary Navier-Stokes equations. The essential part of the talk will be addressed the so-called mild bounded ancient solutions. The Conjecture is that {\it any mild bounded ancient solution is a constant}, which should be identically zero in the case of the half space. The validity of the Conjecture would rule out Type I blowups that have the same kind of singularity as possible self-similar solutions. I am going to list known cases for which the Conjecture has been proven: the Stokes system, the 2D Navier-Stokes system, axially symmetric solutions in the whole space. Very little is known in the case of the half space. Other type of ancients solutions to the Navier-Stokes equations will be mentioned as well.

  • May 5, 2015, Tuesday, 5:15pm, Hill 705, Rutgers University

    Speaker: Fernando Marques, Princeton University

    Title: Multiparameter sweepouts and the existence of minimal hypersurfaces

    Abstract: It follows from the work of Almgren in the 1960s that the space of unoriented closed hypersurfaces, in a compact Riemannian manifold M, endowed with the flat topology, is weakly homotopically equivalent to the infinite dimensional real projective space. Together with Andre Neves, we have used this nontrivial structure, and previous work of Gromov and Guth on the associated multiparameter sweepouts, to prove the existence of infinitely many smooth embedded closed minimal hypersurfaces in manifolds with positive Ricci curvature and dimension at most 7. This is motivated by a conjecture of Yau (1982). We will discuss this result, the higher dimensional case and current work in progress on the problem of the Morse index.

  • March 27, 2015, Friday, 3:00pm, Room 314, Fine Hall, Princeton University

    Speaker: William Minicozzi, MIT

    Title: Uniqueness of blowups and Lojasiewicz inequalities

    Abstract: The mean curvature flow (MCF) of any closed hypersurface becomes singular in finite time. Once one knows that singularities occur, one naturally wonders what the singularities are like. For minimal varieties the first answer, by Federer-Fleming in 1959, is that they weakly resemble cones. For MCF, by the combined work of Huisken, Ilmanen, and White, singularities weakly resemble shrinkers. Unfortunately, the simple proofs leave open the possibility that a minimal variety or a MCF looked at under a microscope will resemble one blowup, but under higher magnification, it might (as far as anyone knows) resemble a completely different blowup. Whether this ever happens is perhaps the most fundamental question about singularities. We will discuss the proof of this long standing open question for MCF at all generic singularities and for mean convex MCF at all singularities. This is joint work with Toby Colding.

  • March 27, 2015, Friday, 4:15pm, Room 314, Fine Hall, Princeton University

    Speaker: Luis Silvestre, University of Chicago

    Title: $C^{1,\alpha}$ regularity for the parabolic homogeneous p-Laplacian equation

    Abstract: It is well known that p-harmonic functions are $C^{1,\alpha}$ regular, for some $\alpha>0$. The classical proofs of this fact uses variational methods. In a recent work, Peres and Sheffield construct p-Harmonic functions from the value of a stochastic game. This construction also leads to a parabolic versions of the problem. However, the parabolic equation derived from the stochastic game is not the classical parabolic p-Laplace equation, but a homogeneous version. This equation is not in divergence form and variational methods are inapplicable. We prove that solutions to this equation are also $C^{1,\alpha}$ regular in space. This is joint work with Tianling Jin.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2014 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Antonio Ache)

  • Dec. 4, 2014, Thursday, 4:30pm, Fine 214, Princeton University

    Speaker: Sigurd Angenent, University of Wisconsin, Madison

    Title: Mean Curvature Flow of Cones

    Abstract: For smooth initial hypersurfaces one has short time existence and uniqueness of solutions to Mean Curvature Flow. For general initial data Brakke showed that varifold solutions exist, but that they need not be unique if the initial data are non smooth. In this talk I will discuss the multitude of solutions to MCF that exist if the initial hypersurface is a cone that is smooth except at the origin. Some of the examples go back to older work with Chopp, Ilmanen, and Velazquez, other examples are recent.

  • Dec. 4, 2014, Thursday, 5:30pm, Fine 214, Princeton University

    Speaker: John Lott, University of California, Berkeley,

    Title: Geometry of the space of probability measures

    Abstract: The space of probability measures, on a compact Riemannian manifold, carries the Wasserstein metric coming from optimal transport. Otto found a remarkable formal Riemannian metric on this infinite-dimensional space. It is a challenge to make rigorous sense of the ensuing formal calculations, within the framework of metric geometry. I will describe what is known about geodesics, curvature, tangent spaces (cones) and parallel transport.

  • Oct. 8, 2014, Weds., 4:45pm, Hill 705

    Speaker: Panagiota Daskalopoulos, Columbia University

    Title: Ancient solutions to geometric flows

    Abstract: We will discuss ancient or eternal solutions to geometric parabolic partial differential equations. These are special solutions that appear as blow up limits near a singularity. They often represent models of singularities. We will address the classification of ancient solutions to geometric flows such as the Mean Curvature flow, the Ricci flow and the Yamabe flow, as well as methods of constructing new ancient solutions from the gluing of two or more solitons. We will also include future research directions.

  • Oct. 8, 2014, Weds., 5:45pm, Hill 705

    Speaker: Lan-Hsuan Huang, University of Connecticut

    Title: Geometry of asymptotically flat graphical hypersurfaces in Euclidean space

    Abstract: We consider a special class of asymptotically flat manifolds of nonnegative scalar curvature that can be isometrically embedded in Euclidean space as graphical hypersurfaces. In this setting, the scalar curvature equation becomes a fully nonlinear equation with a divergence structure, and we prove that the graph must be weakly mean convex. The arguments use some intriguing relation between the scalar curvature and mean curvature of the graph and the mean curvature of its level sets. Those observations enable one to give a direct proof of the positive mass theorem in this setting in all dimensions, as well as the stability statement that if the ADM masses of a sequence of such graphs approach zero, then the sequence converges to a flat plane in both Federer-Flemings flat topology and Sormani-Wenger's intrinsic flat topology.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2014 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Antonio Ache)

  • April 30, 2014, Weds., 2:00pm, Jadwin A06, Princeton University

    Speaker: Fanghua Lin, Courant Institute

    Title: Large N asymptotics of Optimal partitions of Dirichlet eigenvalues

    Abstract: In this talk, we will discuss the following problem: Given a bounded domain . i n R^n, and a positive energy N, one divides . into N subdomains, .j,j=1,2,...,N. We consider the so-called optimal partitions that give the least possible value for the sum of the first Dirichelet eigenvalues on these sumdomains among all a dmissible partitions of $\Omega$.

  • April 30, 2014, Weds., 3:15pm, Jadwin A06, Princeton University

    Speaker: Bruce Kleiner, Courant Institute

    Title: Ricci flow through singularities

    Abstract: It has been a long-standing problem in geometric analysis to find a good definition of generalized solutions to the Ricci flow equation that would formalize the heuristic idea of flowing through singularities. I will discuss a notion in the 3-d case that has good analytical properties, enabling one to prove existence and compactness of solutions, as well as a number of structural results. It may also be used to partly address a question of Perelman concerning the convergence of Ricci flow with surgery to a canonical flow through singularities. This is joint work with John Lott.

  • March 11, 2014, Tuesday, 4:45pm, Hill 525, Rutgers University

    Speaker: Peter Constantin, Princeton University

    Title: Long time behavior of forced 2D SQG equations

    Abstract: We prove the absence of anomalous dissipation of energy for the forced critical surface quasi-geostrophic equation (SQG) in {\mathbb {R}}^2 and the existence of a compact finite dimensional golbal attractor in {\mathbb T}^2. The absence of anomalous dissipation can be proved for rather rough forces, and employs methods that are suitable for situations when uniform bounds for the dissipation are not available. For the finite dimensionality of the attractor in the space-periodic case, the global regularity of the forced critical SQG equation needs to be revisited, with a new and final proof. We show that the system looses infinite dimensional information, by obtaining strong long time bounds that are independent of initial data. This is joint work with A. Tarfulea and V. Vicol.

  • March 11, 2014, Tuesday, 5:45pm, Hill 525, Rutgers University

    Speaker: Mihalis Dafermos, Princeton University

    Title: The linear stability of the Schwarzschild solution under gravitational perturbations in general relativity

    Abstract: I will discuss joint work with G. Holzegel and I. Rodnianski showing the linear stability of the celebrated Schwarzschild black hole solution in general relativity.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2013 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Luc Nguyen)

  • Tuesday, Dec. 3, 4:30pm, Hill 705, Rutgers University

    Speaker: Gaoyong Zhang, Polytechnic Institute of New York University

    Title: The logarithmic Minkowski problem

    Abstract: The logarithmic Minkowski problem asks for necessary and sufficient conditions in order that a nonnegative finite Borel measure in (n-1)-dimensional projective space be the cone-volume measure of the unit ball of an n-dimensional Banach spa ce. The solution to this problem is presented. Its relation to conjectured geometric inequalities that are stronger than the classical Brunn-Minkowski inequality will be explained.

  • Tuesday, Dec. 3, 5:30pm, Hill 705, Rutgers University

    Speaker: Sergiu Klainerman, Princeton University

    Title: On the Reality of Black Holes

  • Friday, Oct. 4, 4:15pm, Fine Hall 110, Princeton University

    Speaker: Natasa Sesum, Rutgers University

    Title: Yamabe flow, its singularity profiles and ancient solutions

    Abstract: We will discuss conformally flat complete Yamabe flow and show that in some case s we can give the precise description of singularity profiles close to the extin ction time of the solution. We will also talk about a construction of new compac t ancient solutions to the Yamabe flow. This is a joint work with Daskalopoulos, King and Manuel del Pino

  • Friday, Oct. 4, 3:00pm, Fine Hall 110, Princeton University

    Speaker: Jeff Viaclovsky, University of Wisconsin-Madison

    Title: Critical metrics on connected sums of Einstein four-manifolds

    Abstract: I will discuss a gluing procedure designed to obtain canonical metrics on connected sums of Einstein four-manifolds. The main application is an existence result, using two well-known Einstein manifolds as building blocks: the Fubini-Study metric on CP^2, and the product metric on S^2 x S^2. Using these metrics in various gluing configurations, critical metrics are found on connected sums for a specific Riemannian functional, which depends on the global geometry of the factors. This is joint work with Matt Gursky.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2013 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Luc Nguyen)

  • Tuesday, April 23, 5:30pm, Hill 425, Rutgers University

    Speaker: Camillo De Lellis, Zurich

    Title: Quantitative rigidity estimates

    Abstract: For many classical rigidity questions in differential geometry it is natural to ask to which extent they are stable. I will review several recent results in the literature. A typical example is the following: there is a constant $C$ such th at, if $Sigma$ is a $2$-dimensional embedded closed surface in $R^3$, then $min_ lambda |A- lambda g|_{L^2} leq C |A - {rm tr A} g/2|_{L^2}$, where $A$ is the se cond fundamental form of the surface and $g$ the Riemannian metric as a submanif old of $R^3$.

  • Tuesday, April 23, 4:30pm, Hill 425, Rutgers University

    Speaker: Xiaochun Rong, Rutgers University

    Title: Degenerations of Ricci Flat Kahler Metrics under extremal transitions and flops

    Abstract: We will discuss degeneration of Ricci-flat Kahler metrics on Calabi-Yau manifold s under algebraic geometric surgeries: extremal transitions or flops. We will pr ove a version of Candelas and de la Ossa's conjecture: Ricci-flat Calabi-Yau man ifolds related via extremal transitions and flops can be connected by a path con sisting of continuous families of Ricci-flat Calabi-Yau manifolds and a compact metric space in the Gromov-Hausdorff topology. This is joint work with Yuguang Zhang

  • Friday, March 1, 4:00pm, Fine Hall 110, Princeton University

    Speaker: Jian Song, Rutgers University

    Title: Analytic minimal model program with Ricci flow

    Abstract: I will introduce the analytic minimal model program proposed by Tian and myself to study formation of singularities of the Kahler-Ricci flow. We also construct geometric and analytic surgeries of codimension one and higher codimensions equ ivalent to birational transformations in algebraic geometry by Ricci flow.

  • Friday, March 1, 3:00pm, Fine Hall 110, Princeton University

    Speaker: Antonio Ache, Princeton University

    Title: On the uniqueness of asymptotic limits of the Ricci flow

    Abstract: Given a compact Riemannian manifold we consider a solution of a normalization of the Ricci flow which exists for all time and such that both the full curvature tensor and the diameter of the manifold are uniformly bounded along the flow. It was proved by Natasa Sesum that any such solution of the normalized Ricci flow is sequentially convergent to a shrinking gradient Ricci soliton and moreover the limit is independent of the sequence if one assumes that one of the limiting solitons satisfies a certain integrability condition. We prove that this integrability condition can be removed using an idea of Sun and Wang for studying the stability of the Kaehler-Ricci flow near a Kaehler-Einstein metric. The method relies on the monotonicity of Perelman's W-functional along the Ricci flow and a Lojasiewicz-Simon inequality for the mu-functional. If time permits we will compare this result with recent Theorems on the stability of the Ricci flow.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2012 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Luc Nguyen)

  • Thursday, September 13, 5:00pm, Hill 705, Rutgers University

    Speaker: Jie Qing, University of California, Santa Cruz

    Title: Hypersurfaces in hyperbolic space and conformal metrics on domains in sphere

    Abstract: In this talk I will introduce a global correspondence between properly immersed horospherically convex hyper surfaces in hyperbolic space and complete conforma l metrics on subdomains in the boundary at infinity of hyperbolic space. I will discuss when a horospherically convex hypersurface is proper, when its hyperboli c Gauss map is injective, and when it is embedded. These are expected to be usef ul to the understandings of both elliptic problems of Weingarten hypersurfaces i n hyperbolic space and elliptic problems of complete conformal metrics on subdom ains in sphere.

  • Thursday, September 13, 4:00pm, Hill 705, Rutgers University

    Speaker: Alessio Figalli, University of Texas, Austin

    Title: Regularity Results For Optimal Transport Maps

    Abstract: Knowing whether optimal maps are smooth or not is an important step towards a qualitative understanding of them. In the 90's Caffarelli developed a regularity theory on R^n for the quadratic cost, which was then extended by Ma-Trudinger-Wang and Loeper to general cost functions which satisfy a suitable structural condition. Unfortunately, this condition is very restrictive, and when considered on Riemannian manifolds with the cost given by the squared distance, it is satisfied only in very particular cases. Hence the need to develop a partial regularity theory: is it true that optimal maps are always smooth outside a "small" singular set? The aim of this talk is to first review the "classical" regularity theory for optimal maps, and then describe some recent results about their partial regularity.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Spring 2012 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Luc Nguyen)

  • Monday, April 30, 4:30-6:30pm, Fine Hall 110, Princeton University

    Speaker: Andre Neves, Imperial College

    Title: Min-max theory and the Willmore Conjecture

    Abstract: In 1965, T. J. Willmore conjectured that the integral of the square of the mean curvature of any torus immersed in Euclidean three-space is at least 2 pi^2. I w ill talk about my recent joint work with Fernando Marques in which we prove this conjecture using the min-max theory of minimal surfaces.

  • Tuesday, March 6, 5:00pm, Hill 705, Rutgers University

    Speaker: Paul Yang, Princeton University

    Title: Compactness of conformally compact Einstein metrics

    Abstract:

  • Tuesday, March 6, 4:00pm, Hill 705, Rutgers University

    Speaker: Ovidiu Savin, Columbia University

    Title: The thin one-phase problem

    Abstract: We discuss regularity properties of solutions and their free boundaries for minimizers of the thin Bernoulli problem. We show that Lipschitz free boundaries are classical and we obtain a bound on the Hausdorff dimension of the singular set of the free boundary of minimizers. This is a joint work with D. De Silva.

    Joint Princeton-Rutgers Seminar on Geometric PDE's ---- Fall 2011 (Organizers on Rutgers side: Yanyan Li, Zheng-Chao Han, Natasa Sesum, Jian Song; Coordinator on Princeton side: Luc Nguyen)

  • Thursday, December 8, 5:00pm, Fine Hall 110, Princeton University

    Speaker: Haim Brezis, Rutgers University

    Title: Sobolev maps with values into the circle

    Abstract: Real-valued Sobolev functions are well-understood and play an immense role. By c ontrast, the theory of Sobolev maps with values into the unit circle is not yet sufficiently developed. Such maps occur in a number of physical problems. The re ason one is interested in Sobolev maps, rather than smooth maps is to allow maps with point singularities, such as x/|x| in 2-d, or line singularities in 3-d wh ich appear in physical problems. It turns out that these classes of maps have a rich structure. Geometrical and topological effects are already conspicuous, eve n in this very simple framework. On the other hand, the fact that the target spa ce is the circle (as opposed to higher-dimensional manifolds) offers the option to study their lifting and raises some tough questions in Analysis.

  • Thursday, December 8, 4:00pm, Fine Hall 110, Princeton University

    Speaker: Gang Tian, Princeton University

    Title: Bounding scalar curvature along Kahler-Ricci flow

    Abstract:

  • Thursday, Oct. 27, 5:00pm, Hill 552, Rutgers University

    Speaker: Nassif Ghoussoub , University of British Columbia

    Title: A self-dual polar decomposition for vector fields

    Abstract: I shall explain how any non-degenerate vector field on a bounded domain of $R^n $ is monotone modulo a measure preserving involution $S$ (i.e., $S2=Identity$). This is to be compared to Brenier's polar decomposition which yields that any su ch vector field is the gradient of a convex function (i.e., cyclically monotone) modulo a measure preserving transformation. Connections to mass transport --whi ch is at the heart of Brenier's decomposition-- is elucidated. This is joint wor k with A. Momeni.

  • Thursday, Oct. 27, 4:00pm, Hill 552, Rutgers University

    Speaker: Aaron Naber, MIT

    Title: Quantitative Stratification and regularity for Einstein manifolds, harmonic maps and minimal surfaces

    Abstract: In this talk we discuss new techniques for taking ineffective local, e.g. tangent cone, understanding and deriving from this effective estimates on regularity. Our primary applications are to Einstein manifolds, harmonic maps between Riemannian manifolds, and minimal surfaces. For Einstein manifolds the results include, for all p<2, 'apriori' L^p estimates on the curvature |Rm| and the much stronger curvature scale r_{|Rm|}(x)=max{r>0:sup_{B_r(x)}|Rm|leq r^{-2}}. If we assume additionally that the curvature lies in some L^q we are able to prove that r^{-1}_{|Rm|} lies in weak L^2q. For minimizing harmonic maps f we prove W^{1,p}cap W^{2,p/2} estimates for p<3 for f and the stronger likewise defined regularity scale. These are the first gradient estimates for p>2 and the first L^p estimates on the hessian for any p. The estimates are sharp. For minimizing hypersurfaces we prove L^p estimates for p<7 for the second fundamental form and its regularity scale. The proofs include a new quantitative dimension reduction, that in the process stengthens hausdorff estimates on singular sets to minkowski estimates. This is joint work with Jeff Cheeger.