Wed 15 Jan 2020 13:0015:00 UCL Gordon Sq 1618 Room 101

Ancient low entropy flows, mean convex neighborhoods, and uniqueness Speaker: Felix Schulze (UCL) Abstract: In this talk we will discuss the recent proof of the positive mean curavture neighborhood conjecture of ChoiHaslhoferHershkovits for the mean curvature flow of embedded surfaces in R^3. The proof hinges on the complete classification of ancient solutions with low entropy. We will discuss the strategy and give an outline of the proof, but will also focus on the further implications of the result.
See the paper `Ancient low entropy flows, mean convex neighborhoods, and uniqueness', by K. Choi, R. Haslhofer and O. Hershkovits, https://arxiv.org/abs/1810.08467
Term 3 20182019
The Seiberg Witten equations.
The SeibergWitten equations are a system of nonlinear PDEs defined on any Riemannian 4manifold. They have the remarkable property that the space of solutions (modulo gauge) is compact. When this space is zero dimensional, the number of solutions is independent of the Riemannian metric, giving an invariant of the underlying smooth 4manifold. This invariant is intimately connected to the geometry and differential topology of themanifold. For example they enable one to detect different smooth structures on the same topological 4manifold, the nonexistence of a symplectic structure, the uniqueness of the symplectic structure on CP^2... The aim of the reading seminar is to give a "bird'seye view" of the SeibergWitten equations and their applications, unfortunately only giving sketches of some of the more technical aspects of the subject (notably Taubes' work on the SeibergWitten invariants of symplectic 4manifolds). Finally, time permitting, we will look briefly at variations of the SeibergWitten equations and their applications in G_2 geometry.
Wed 24 April 2019 13:1514:45 UCL Christopher Ingold Building XLG1 Chemistry LT

The SeibergWitten invariant of a compact 4manifold Speaker: Joel Fine (ULB) Abstract: I will outline the definition of the SeibergWitten invariant of a compact 4manifold. I will try and explain how the invariant fits into a framework of "Fredholm differential invariants," due to Donaldson. The specific case of the SeibergWitten equations is in some sense the most straightforward example, because compactness of the space of solutions is automatic, but to even state the equations requires quite a lot of geometric background. I will give a rapid overview of this (Spinc structures and Dirac operators) before describing the Fredholm theory and compactness result. Finally, time permitting, I will explain why the number of solutions to the SeibergWitten equations is an invariant of the underlying smooth 4manifold. 
Wed 1 May 2019 13:1514:45 UCL Drayton House B03 Ricardo LT

Compactness, SeibergWitten invariants of K�hler 4folds and the relation between SeibergWitten and GromovWitten invariants Speaker: Daniel Platt (UCL/LSGNT) Abstract: In the talk I will explain why the moduli space of solutions to the SWequations is compact. Following this I will explain the canonical Spin^c structure and Dirac operator on K�hler 4folds, and use this to compute their SWinvariants. The talk will end with a nod to the relation between SWinvariants and GromovWitten invariants discovered by Taubes. 
Wed 15 May 2019 13:3014:45 UCL Drayton House B03 Ricardo LT

Defining the SeibergWitten invariant and applications to differential topology of 4manifolds Speaker: Joel Fine (ULB) Abstract: I will complete the steps in the definition of the Seiberg?Witten invariant for compact 4manifolds. I will then explain applications to 4manifold topology, such as the existence of homeomorphic but not diffeomorphic 4manifolds, as well as Donaldson?s diagonalisability theorem. 
Wed 22 May 2019 13:1514:45 UCL Drayton House B03 Ricardo LT

SeibergWitten invariants of symplectic fourmanifolds: Taubes' theorems Speaker: Ralph Klaasse (ULB) Abstract: In this talk we will take a look at the behavior of the SeibergWitten invariants on symplectic fourmanifolds. We will show that the invariant of the canonical Spin^c structure has modulus 1, and sketch how this lead Taubes to be able to prove an equivalence between the SeibergWitten and (modified) GromovWitten invariants. In particular, we will discuss how from an appropriate sequence of SeibergWitten solutions, one can extract a pseudoholomorphic curve. 
Wed 29 May 2019 13:1514:45 UCL Cruciform Building B404  LT2

Wall crossing for SeibergWitten invariants. And maybe if there's time, the uniqueness of the symplectic structure on CP^2 Speaker: Joel Fine (ULB) Abstract: When b_+>1, the SeibergWitten invariant does not depend on the choice of perturbation used in the equations. When b_+=1 however the space of perturbations is split by a codimension 1 wall. I will explain that when the perturbation crosses this wall the corresponding invariant jumps by 1. If there's time (which, frankly, given my ability to judge these things, is unlikely) I will explain a beautiful application of SW theory to symplectic topology: CP^2 admits a unique symplectic structure up to diffeomorphisms and overall scale. (This is a combination of arguments due to Gromov and Taubes.) 
Term 2 20182019
Recent progress in the theory of Poincar�Einstein 4manifolds.
A Poincar�Einstein metric on a compact manifold with boundary determines a conformal structure on the boundary, called its ?conformal infinity?. (The paradigm is hyperbolic space itself, whose conformal infinity is the standard conformal structure on the sphere.) A longstanding goal in the field, first proposed by Michael Anderson, is to develop a degree theory for the map which sends a Poincar�Einstein metric on a given 4manifold to its conformal infinity. If one could define the degree of this map and prove it were nonzero it would follow that ALL conformal structures on the boundary could be filled by Poincar�Einstein metric on the interior! The crux is to show the map is proper. There has been exciting recent progress on this problem, in recent papers of ChangGe and ChangGeQing, which prove compactness results for a sequence of Poincar�Einstein metrics on a 4manifold, assuming that their conformal infinities converge, together with some other supplementary conditions. After some talks setting the scene, we hope to go over the details of the following two papers: https://arxiv.org/abs/1809.05593, https://arxiv.org/abs/1811.02112.
Wed 16 Jan 2019
13:1514:45 UCL Maths Department Room 707

An introduction to the Dirichlet problem for Poincar�Einstein 4manifolds, Anderson?s programme and the papers of ChangGe and ChangGeQing Speaker: Joel Fine (ULB) Abstract: I will begin by introducing Poincar�Einstein metrics: these are asymptotically hyperbolic metrics on the interior of a compact manifold with boundary. A Poincar�Einstein metric determines a conformal structure on the boundary called its ?conformal infinity", the prototype being hyperbolic space itself with conformal infinity the standard structure on the sphere. Given a choice of conformal structure on the boundary, the Dirichlet problem asks for a Poincar�Einstein metric on the interior with this structure as its conformal infinity. It is a deep problem. From the analytic point of view, one must solve a nonlinear geometrically elliptic PDE whose symbol degenerates at infinity. I will describe an approach to this problem in 4dimensions using Fredholm degree theory, which was suggested by Anderson. Whether this can be made to work is still an open question, but there has been recent exciting progress in the papers of ChengGe and ChengGeQing. I will state their results and try to explain the intuition behind their somewhat complicated hypotheses. 
Wed 23 Jan 2019 13:1514:45 UCL Maths Department Room 707

Linear analysis on asymptotically hyperbolic manifolds and the theorem of GrahamLee Speaker: Marco Usula (ULB) Abstract: The theorem of Graham and Lee states that, for every small perturbation of the conformal infinity of the hyperbolic metric, there is a PoincareEinstein metric on the ball whose conformal infinity is the perturbed conformal class. The proof of the theorem relies on Fredholm properties of the linearized Einstein equation modulo gauge. In this seminar, we will briefly introduce Mazzeo's elliptic theory of 0differential operators, and we will use it to prove the theorem of Graham and Lee. 
Wed 30 Jan2019 13:3014:45 UCL Maths Department Room 706

Qcurvature, conformal powers of the Laplacian and the FeffermanGraham compactification Speaker: Joel Fine (ULB) Abstract: Let g be a Poincar�Einstein metric. Given a metric h representing the conformal infinity of g, FeffermanGraham introduced a canonical choice of compactification x^2g, restricting to h on the boundary. This compactification has the special property that it has vanishing Qcurvature. These compcatifications are essential in the papers of ChangGe and ChangGeQing. I will firstly explain one way to define Q curvature together with the closely related sequence of differential operators which in conformal geometry play the role of powers of the Laplacian. I will then prove existence and uniqueness of the FeffermanGraham compactification and the vanishing of its Qcurvature. This all follows the paper ?Qcurvature and Poincar� metrics? by Fefferman and Graham, available on the arxiv: https://arxiv.org/abs/math/0110271 
Wed 6 Feb 2019 13:1514:45 UCL Maths Department Room 707

A first step in the proof of ChangGe's result: Blowup analysis near the boundary Speaker: Bruno Premoselli (ULB) Abstract: In this talk we start to describe the proof of ChangeGe's compactness result for conformally compactified Poincar�Einstein metrics. Assuming technical results that will be addressed in later talks (among which epsilonregularity) we will briefly describe the strategy of proof and study in detail the first step of the blowup analysis, namely when blowup occurs near the boundary. 
Wed 13 Feb 2019 13:0514:35 UCL Maths Department Room 706

Interior Blowup Analysis and completing the proof of ChangGe's Compactness Theorem Speaker: Andrew McLeod (UCL) Abstract: Following on from last week's talk, we rule our curvature blow up in the interior (I.e. far away from the boundary). It is within this step that the imposed topological restrictions on our sequence are vital. Once armed with uniform (in i) curvature bounds we may then complete the proof of the main compactness result, Theorem 1.1 in ChangGe. 
Wed 20 Feb 2019 13:1514:45 UCL Maths Department Room 706

Epsilonregularity I Speaker: Daniel Platt (UCL) Abstract: To extract a converging subsequence of metrics we need high regularity of the metrics in the interior. epsilonregularity can boost the a priori C^1regularity to a certain version of C^{k+1}regularity. It will be instructive to see how the assumptions from the main theorem (e.g. boundedness of Yamabe constant) and properties of the FeffermanGraham compactification are used very explicitly in the proof of epsilonregularity. This is the first out of two talks presenting epsilonregularity. 
Wed 27 Feb 2019 13:1514:45 UCL Maths Department Room 706

Epsilonregularity II Speaker: Konstantinos Leskas (UCL) Abstract: In this talk we shall see how to iterate Theorem 3.1 to obtain the L^\infty bounds on the derivatives of the curvature tensor up to order k2. Then we finish the proof of Theorem 3.1, trying to clarify most of its steps. 
Wed 6 Mar 2019 13:1514:45 UCL Maths Department Room 707

Some useful Identities on the Boundary Speaker: Benjamin Aslan (UCL) Abstract: In this talk, several tensor identities which have been used in the talks on Epsilon Regularity will be proven. For example, we will see how the Stensor transforms under conformal changes (Lemma 2.3) of the metric and find expressions for the kth covariant derivative of the Weyltensor, Schoutentensor and the Scalar Curvature (Lemma 2.8 and 2.9). 
Wed 13 Mar 2019 13:1514:45 UCL Maths Department Room 706

Injectivity radius bounds via blowup Speaker: Reto Buzano (QMUL) Abstract: In this talk, we show that for the FeffermanGraham compactification of a conformally compact Einstein 4manifold with positive Yamabe constant at conformal infinity, a bound on the intrinsic injectivity radius on the boundary implies a bound on the intrinsic injectivity radius in the interior. The proof relies on a blowup argument and a Theorem of LiQingShi. 
Wed 20 Mar 2019 13:1514:45 UCL Maths Department Room 706

Sobolev inequalities and the compactness of FeffermanGraham compactifications Speaker: Felix Schulze (UCL) Abstract: We show how the necessary Sobolev inequalities are obtained which replace the assumption of a positive lower bound on the first and second Yamabe constants in the proof in the paper of ChangGe of the compactness of FeffermanGraham compactifications. We further demonstrate how these Sobolev inequalities can be used to obtain the compactness under suitable assumtions on the boundary Yamabe metrics, the nonconentration of the Stensor, and the vanishing of the second homology. 
Wed 27 Mar 2019 13:1514:45 UCL Maths Department Room 706

Global uniqueness of the GrahamLee metrics on the 4ball Speaker: Jason D. Lotay (Oxford) Abstract: Recall that for every conformal class c on the 3sphere, sufficiently near the conformal class of the standard round metric, a theorem of GrahamLee gives a PoincareEinstein metric g on the 4ball which has c as its conformal infinity. Moreover, g is locally unique modulo gauge. It has been a longstanding open question whether g is globally unique. We will describe the proof of this uniqueness theorem, due to ChangGeQing, which is the key application thus far of their compactness theory. 
Term 1 20182019
Mon 1 October 2018 14:0016:00 Foster Court 233

A beginner?s guide to the NashMoser implicit function theorem Speaker: Michael Singer (UCL) Abstract: The NashMoser theorem has a fearsome reputation in some quarters, but the basic ideas are quite simple. In this talk I shall discuss a simple version of the theorem as presented in the short paper of X. SaintRaymond, A simple NashMoser implicit function theorem, L?enseignement Mathematique, (2) 35 (1989), as well as some motivating examples. 
Mon 8 October 2018 14:0016:00 Foster Court 114

MinMax and Geometry Speaker: Huy Nguyen (QMUL) Abstract: In this talk, I will give a broad and notthattechnical overview of recent results in minmax and its applications to geometry. In particular, I will focus on the AllenCahn and GinzburgLandau equations and their relationship to minimal surfaces. 
Mon 15 October 2018 14:0016:00 Birckbeck Gordon Sq (43) G01 
Existence of critical points of Ginzburg?Landau functionals Speaker: Florian Litzinger (QMUL) Abstract: Critical points of Ginzburg?Landau functionals can be found by means of the minmax procedure. First we prove a fairly general version of the Saddle Point Theorem for C^1functionals satisfying the Palais?Smale condition. Following Section 2 of D. Stern's paper, we then apply the construction to the family of Ginzburg?Landau functionals on a compact Riemannian manifold, establishing the existence of nontrivial critical points in the Sobolev space H^1.

Mon 22 October 2018 14:0016:00 Birckbeck Gordon Sq (43) G01 
Lower bounds on the energies Speaker: Gianmichele di Matteo (QMUL) Abstract: In this talk, we will prove the lower bounds on the energies of the minimax critical points constructed in the previous section, needed to ensure the nontriviality of the energy concentration set. See also section 3 in the paper by D. Stern. 
Mon 29 Ocotober 2018 14:0016:00 Birckbeck Gordon Sq (43) G01 
?ellipticity for the GinzburgLandau equation Speaker: Huy Nguyen (QMUL) Abstract: In this talk, we will consider the proof of a key estimate for the GinzburgLandau minmax procedure, the ?ellipticity. This estimate was used to prove the upper bounds for the minmax values for the GinzburgLandau equation. They key ideas are the monotonicity formula for penalised harmonic maps and a Hodgede Rham decomposition of the phase function. 
Mon 12 November 2018 14:0016:00 Birckbeck Gordon Sq (43) G01

Upper bounds for the energies Speaker: Francesco di Giovanni (UCL) Abstract: In this talk we present Stern's construction of upper bounds for the minmax constants of the GL Energy functional with logarithmic growth in epsilon. Along with the previously discussed existence of analogous lower bounds, that allows to complete the proof of Theorem 1.1 in Stern's paper. 
Mon 19 November 2018 14:0016:00 Birckbeck Gordon Sq (43) G01

Varifolds and Rectifiability I Speaker: Costante Bellettini (UCL) Abstract: Integral varifolds are ?singular submanifolds?. The necessity for extending the class of submanifolds beyond smooth ones is evident whenever a limiting process is involved. The drawback of extending the class is that the the set where smoothness fails could be huge. We will address the notions of rectifiability, of first and second variation of their area, and of generalized mean curvature. Under suitably mild assumptions on the generalized mean curvature, Allard?s theorem provides the foundational steps in the regularity theory (giving a bit of regularity) and in the compactness theory. The latter requires the introduction of a more general notion of varifolds, which is also useful for other purposes (for example it naturally appears in the paper we are reading) and for which one can still talk of "area" and "mean curvature" in a suitable sense. 
Thu 29 November 2018 14:0016:00 Cruciform Building B404  LT2 
Varifolds and Rectifiability II Speaker: Fritz Hiesmayr (Cambridge) Abstract: This is the second talk of our introduction into the basics of varifolds and rectifiability. After briefly recalling the notions from the previous week (including general varifolds) we will state Allard's regularity and compactness theorems (without proof). We then move on to the monotonicity formula for stationary varifolds (and time permitting give a proof) and define the notion of density. We end the talk with a statement of Preiss' theorem, which gives conditions under which a Radon measure is rectifiable. 
Mon 3 December 2018 14:0016:00 Birckbeck Gordon Sq (43) G01

Rectifiability of the Ginzburg Landau limit Speaker: Ben Lambert (UCL) Abstract: We will see that the Ginzburg Landau solutions constructed earlier in the reading group are "generalised varifolds" (to be defined). We aim to prove that the limit of these generalised varifolds is a rectifiable varifold. The key step in this is to prove suitable density estimates, which we will prove via a series of reductions. 
Mon 10 December 2018 14:0016:00 Birckbeck Gordon Sq (43) G01

Rectifiability of the Ginzburg Landau limit  part II Speaker: Felix Schulze (UCL) Abstract: I will complete the proof of the rectifiability of the limiting varifold arising form the GinzburgLandau approximation. 
Wed 25 April 2018 13:0014:45 UCL Room D103 
An introduction to pseudoholomorphic curves Speaker: Kim Moore (UCL) Abstract: We will describe the basic theory of pseudoholomorphic curves that will be needed for future seminars, including the linearisation of the nonlinear CauchyRiemann operator and positivity of intersections. 
Wed 2 May 2018 13:0014:45 UCL Room D103 
The moduli space of pseudoholomorphic curves Speaker: Ben Lambert (UCL) Abstract: We will describe the moduli space theory of pseudoholomorphic curves as needed for future seminars, particularly focusing on the issue of transversality. 
Wed 9 May 2018 13:0014:45 UCL Room D103 
Estimates for pseudoholomorphic curves Speaker: Thomas Koerber Abstract: We will describe the estimates for pseudoholomorphic disks and cylinders, and the removable singularities theorem for pseudoholomorphic maps, as required in applications in symplectic topology. 
Wed 16 May 2018 13:0014:45 UCL Room D103 
Proof of Gromov's compactness theorem for pseudoholomorphic curves Speaker: Chris Evans (UCL) Abstract: We will describe the proof of the compactness theorem for pseudoholomorphic curves, building on the theory in previous seminars, which will include the bubbling analysis. 
Wed 23 May 2018 13:0014:45 UCL Room D103 
Gromov's nonsqueezing theorem Speaker: Albert Wood (LSGNT/UCL) Abstract: We will show how the pseudoholomorphic curve theory developed so far in previous seminars allows us to prove the nonsqueezing theorem. 
Wed 17 January 2018 13:0014:45 UCL Maths Department Room 707 
An introduction to harmonic maps Speaker: Costante Bellettini (UCL) Abstract: A harmonic map is, roughly speaking, a critical point for the Dirichlet energy. Depending on the precise requirement, we will distinguish the notions of minimizing harmonic/stationary harmonic/weakly harmonic maps. The weaker notion (the third one) leads to a second order nonlinear elliptic PDE (in weak form). The second notion provides, additionally, a monotonicity formula for the Dirichlet energy. We will overview regularity aspects for these classes of maps and compactness issues, in particular the bubbling phenomenon that occurs when working with weak W^{1,2} convergence (the natural notion, due to the relevant energy). We will overview other related aspects: the criticality, for the exponent p=2, of the PDE from the point of view of elliptic bootstrapping; some special results valid in the case of 2dimensional domains (mostly postponed to the next talk); the lack of a PalaisSmale property; the subtleties associated to the possible lack of approximability of W^{1,2} maps by means of smooth maps and the relation with the topology of the target. 
Wed 24 January 2018 13:0014:45 UCL Maths Department Room 707 
An overview of the SacksUhlenbeck construction and further developments Speaker: Huy Nguyen (QMUL) Abstract: In this seminar, we will discuss aspects of the two dimensional harmonic maps problem. We will discuss some of the regularity theory (Helein's theorem for weakly harmonic maps), the existence theory (SacksUhlenbeck) and bubble tree convergence (Parker, DingTian) . 
Wed 31 January 2018 13:0014:45 UCL Maths Department Room 707 
SacksUhlenbeck Chapter 1 Speaker: Udhav Fowdar (LSGNT/UCL) Abstract: I will start by the basic definitions and relate the critical points of the energy and volume functional. Then I will define branched minimal immersions and sketch the proofs of the main theorems of the first section. 
Wed 7 February 2018 13:0014:45 UCL Maths Department Room 707 
SacksUhlenbeck Chapter 2 Speaker: Fabian Lehmann (LSGNT/UCL) Abstract: Morse theory relates the topology of a compact finite dimensional manifold to the existence of critical points of a Morse function. I will explain that in a similar way a nontrivial topology of the target manifold N gives the existence of nontrivial critical maps for the perturbed energy functional for maps from S^{2} to N. For this it is crucial that the functional satisfies the PalaisSmale condition. 
Wed 21 February 2018 13:0014:45 UCL Maths Department Room 707 
Estimates and Extensions for the Perturbed Problem (SacksUhlenbeck Chapter 3) Speaker: Albert Wood (LSGNT/UCL) Abstract: In the last talk we looked at properties of the perturbed energy functional E_{?}. In this talk we will cover section 3 of the paper, in which we derive important estimates for critical points of this functional, as well as an improved regularity result. 
Fri 2 March 2018 13:0014:30 UCL Maths Department Room 707 
Convergence properties of critical maps of the perturbed problem (SacksUhlenbeck Chapter 4) Speaker: Gianmichele di Matteo (QMUL) Abstract: We will show that the only obstacle to a regular (C^{1}) convergence of the critical maps constructed in the previous chapters, is the presence of at least one minimal sphere near the point where the convergence fails. 
Fri 9 March 2018 13:0015:00 UCL Maths Department Room 707 
Harmonic maps and topology (SacksUhlenbeck Chapter 5) Speaker: Jason Lotay (UCL) Abstract: I will describe some applications of the analytic theory of harmonic maps developed by SacksUhlenbeck. First, I will describe some results providing the existence of energyminimizing harmonic maps representing homotopy classes of maps, when topological obstructions vanish. Second, I will describe how Morse theory can be used in the presence of nontrivial topology to produce harmonic spheres (and thus conformal branched minimal spheres) which may be higher index critical points for the energy (rather than minimizers). 
Wed 21 March 2018 13:0015:00 UCL Maths Department Room 707 
An introduction to Gromov's compactness theorem for pseudoholomorphic curves Speaker: Jason Lotay (UCL) Abstract: I will aim to provide the background to and statement of Gromov's compactness theorem for pseudoholomorphic curves. I will also describe some important results in symplectic topology which are applications of this result. 
Wed 4 October 2017 13:0014:45 KCL Strand Building Room S4.23 
Original proof of positive mass theorem up to dimension 7 Speaker: Mattia Miglioranza (UCL) Abstract: We give an overview of the strategy of the original proof of the positive mass theorem by Schoen and Yau up to dimension 7. 
Wed 11 October 2017 13:0014:45 KCL Strand Building Room S4.23 
Introduction and motivation (Schoen notes Chapter 1) Speaker: Lothar Schiemanowski (Kiel/QMUL) Abstract: In this talk we will introduce three motivations to study scalar curvature and various phenomena unique to it. 
Wed 18 October 2017 12:0013:45 UCL Taviton 14 Room 129 
Positive scalar curvature and the positive mass theorem (Schoen notes Chapter 2 Sections 12) Speaker: Udhav Fowdar (UCL) Abstract: In this talk we shall see how the nonexistence of positive scalar curvature on certain closed manifolds implies the (classical) positive mass theorem. 
Wed 25 October 2017 13:0014:45 KCL Strand Building Room S4.23 
An introduction to minimal slicings (Schoen notes Chapter 2 Section 3 Part 1) Speaker: Albert Wood (UCL) Abstract: Last week, we saw that the Positive Mass Theorem is implied by the nonexistence of a metric on M^{n}#T^{n} with positive scalar curvature. Our ultimate aim, then, is to prove this. The bulk of the remaining work is taken up with the theory of existence and regularity of minimal slicings, which are nested families of submanifolds minimal with respect to a certain weighted volume functional. In this talk, I will explain why we would like to study these objects, and I will prove a key theorem on the path to the PMT: 'Positive scalar curvature implies that an appropriately chosen minimal slicing is Yamabe positive'. 
Wed 1 November 2017 13:0014:45 KCL Strand Building Room S4.23 
Regularity of minimal kslicings: L^2 nonconcentration of the first eigenfunction (Schoen notes Chapter 2 Section 3 Part 2) Speaker: Chris Evans (UCL) Abstract: Last week, we saw how minimal kslicing could be used to prove the positive mass theorem. We now begin the work on regularity by discussing results that guarantee the first eigenfunction of the quadratic form Q_{j} doesn't concentrate around singularities under certain partial regularity assumptions. 
Wed 15 November 2017 13:0014:45 KCL Strand Building Room S4.23 
Homogeneous minimal slicings (Schoen notes Chapter 2 Section 4) Speaker: Ben Lambert and Kim Moore (UCL) Abstract: We will discuss the results of Chapter 4 in the notes and give an overview of how the rest of the proof will follow. 
Wed 22 November 2017 13:0014:45 KCL Strand Building Room S4.23 
Top dimensional singularities (Schoen notes Chapter 2 Section 5) Speaker: Kim Moore (UCL) Abstract: We will discuss the material in Section 5 of the notes, in which it is proved that a positive minimiser for the quadratic form on a volume minimising (nonplanar) cone is homogeneous of strictly negative degree. 
Wed 29 November 2017 13:0015:00 KCL Strand Building Room S4.23 
Cones and compactness of minimal slicings (Schoen notes Chapter 2 Sections 46) Speaker: Ben Lambert (UCL) Abstract: I will make some comments about how we obtain cones in section 4 of the notes before proving convergence of the quadratic forms using a capacity argument. Depending on time and interest, we can also talk about convergence in weighted measure. 
Wed 6 December 2017 13:0014:45 KCL Strand Building Room S4.23 
Completing the compactness theorem (Schoen notes Chapter 2 Sections 67) Speaker: Ben Lambert (UCL) Abstract: We will finish going through the "convergence of u in H^{2}" (that is, we will finish section 6 in the notes). If there is time, we will start proving partial regularity using Federer's dimension reduction technique (section 7 in the notes). 
Wed 13 December 2017 13:0014:45 KCL Strand Building Room S4.23 
Partial regularity and existence of minimal slicings (Schoen notes Chapter 2 Sections 78) Speaker: Fritz Hiesmayr (Cambridge) Abstract: The talk will be in two parts: in the first part we prove that minimal slicings are partially regular. The dimension bound on the singular set of the bottom leaf of the slicing follows inductively via a dimension reduction argument, using the nonexistence of homogeneous 2slicings with an isolated singularity at the origin that was established last week. In the second part we are going to discuss the existence of minimal slicings in manifolds satisfying a topological restriction (this applies in particular for connected sums with a torus as in the compactification theorem). The proof is via a minimisation argument for the weighted volume, carried out in the class of rectifiable currents with integer multiplicity. This corresponds to Sections 7 and 8 in Chao Li's notes, and Section 4 of the SchoenYau paper. 
Thur 27 April 2017 13:0015:00 UCL Maths Department Room 500 
Desingularizing Einstein metrics Speaker: Michael Singer (UCL) Abstract: The goal will be to present Biquard's paper on desingularizing 4dimensional Einstein orbifolds via gluing, including discussions of the obstructions. 
Thurs 11 May 2017 15:3017:30 UCL Maths Department Room 505 
An overview of YangMills flow Speaker: Casey Kelleher (UC Irvine) Abstract: The aim is to provide a discussion of the basics of YangMills flow, including the analogy with harmonic map heat flow, the work of Donaldson and Struwe, and potentially singularities and removal of singularities. 
Wed 17 May 2017 13:0015:00 UCL Maths Department Room 500 
Uhlenbeck gauge construction Speaker: Yang Li (Imperial/LSGNT) Abstract: This talk will focus on the construction of an appropriate gauge in which to study YangMills connection, given by work of Uhlenbeck. 
Wed 24 May 2017 13:0015:00 UCL Roberts Building Room 508 
YangMills flow in dimension 4: part 1 Speaker: Huy Nguyen (QMUL) Abstract: In this first of three talks discussing Waldron's preprint on YangMills flow in dimension 4, the goal will be to discuss the optimal decay estimates in the elliptic case as background and an outline of part of the energy estimates. 
Thurs 1 June 2017 13:0015:00 UCL Maths Department Room 500 
YangMills flow in dimension 4: part 2 Speaker: Huy Nguyen (QMUL) Abstract: I will continue discussing Waldron's preprint on YangMills flow in dimension 4. I'll talk about the optimal decay estimates, an overview of the paper, the monotonicity formula for YangMills flow and epsilonregularity. 
Tues 13 June 2017 13:0015:00 UCL Maths Department Room 500 
YangMills flow in dimension 4: part 3 Speaker: Kim Moore (Cambridge) Abstract: In this final talk discussing Waldron's preprint on YangMills flow in dimension 4, the key steps from the previous talks will be brought together to summarize the proof. 
Wed 1 February 2017 13:0015:00 UCL Maths Department Room 707 
Convergence of the AllenCahn equation to Brakke�s motion by mean curvature Speaker: Felix Schulze (UCL) Abstract: I will present the main results of Ilmanen�s paper on convergence of solutions to the AllenCahn equation to Brakke�s motion by mean curvature. 
Wed 8 February 2017 13:0015:00 UCL Maths Department Room 707 
The minmax construction of AllenCahn critical points Speaker: Fritz Hiesmayr (Cambridge) Abstract: In my talk I will discuss the paper by Guaraco entitled "Minmax for phase transitions and the existence of embedded minimal hypersurfaces" from 2015. After situating the paper in the broader context of the construction of minimal hypersurfaces, I will present its results in two parts: first, the PDE minmax construction, and then the energy upper and lower bounds. Time permitting, I might make a short comparison between the AllenCahn construction and the earlier AlmgrenPitts theory. 
Wed 22 February 2017 13:0015:00 UCL Maths Department Room 707 
Stability and absence of classical singularities for the minimal hypersurface obtained as limit of AllenCahn stable solutions. Speaker: Costante Bellettini (UCL) Abstract: Two weeks ago Fritz described how to construct an index one critical point for the ?AllenCahn functional: a suitable subsequence as ??0 delivers a minimal hypersurface (integral varifold) in the limit. I will describe the contents of Tonegawa and TonegawaWickramasekera, which show respectively how the stability of AllenCahn solutions is inherited by the limit varifold and how to check that the varifold has no classical singularities. These are the properties that enable the use of Wickramasekera's regularity (codimension7 singular set). 
Wed 1 March 2017 13:0015:00 UCL Maths Department Room 707 
CalabiYau metrics on Kummer surfaces Speaker: Eleonora di Nezza (Imperial) Abstract: After Yau proved the Calabi conjecture, showing the existence of K�hler metrics with Ricci curvature identically zero on compact K�hler manifolds with vanishing first Chern class, there has been a lot of use of "gluing constructions" in order to give an almostexplicit description of these metrics in some special cases. In this talk I will present a paper of Donaldson: the goal is to explain a gluing construction for some CalabiYau metrics on K3 surfaces. 
Wed 8 March 2017 13:0015:00 UCL Maths Department Room 707 
Collapsing CalabiYau metrics on K3 surfaces via gluing Speaker: Fabian Lehmann (LSGNT) Abstract: After last week's gluing construction of a CalabiYau metric, this week we will look at Foscolo's recent construction of a family of hyperkahler metrics on the K3 which collapse with bounded curvature outside of finitely many points to T^{3}/Z_{2}. The geometry around points where the curvature blows up is modelled on rescaled ALF gravitational instantons. 
Wed 15 March 2017 13:0015:00 UCL Maths Department Room 707 
Minimal surfaces in Poincar�Einstein manifolds Speaker: Joel Fine (ULB) Abstract: The talk will be loosely based on the article "Renormalized area and properly embedded minimal surfaces in hyperbolic 3manifolds" by Alexakis and Mazzeo. A Poincar�Einstein metric is an Einstein metric on the interior of a manifold with boundary which is asymptotically hyperbolic near the boundary. Such a metric induces a conformal structure on the boundary. They were first systematically studied by Fefferman and Graham as a way to investigate conformal structures. A central problem is to find a Poincar�Einstein metric filling in a given conformal infinity and even count the number of such solutions. Minimal surfaces give a simpler version of this boundary problem: for a fixed Poincar�Einstein metric, given a curve on the boundary, how many minimal surfaces can one find in the interior which meet the boundary at right angles in the given curve? Alexakis and Mazzeo show that, when the ambient manifold has dimension 3, the boundary value map for minimal surfaces is proper, Fredholm of index 0 and so one can define its degree, which �counts� the number of solutions to this Dirichlet type problem. I will explain their proof and then discuss why I hope a similar result should hold for certain ambient manifolds of dimension 4. If there is time, I will try and outline why this may be of interest for the original question of finding a Poincar�Einstein metric with given conformal structure at infinity. 
Wed 22 March 2017 13:0015:00 UCL Maths Department Room 707 
Gluing EguchiHanson metrics and a question of Page Speaker: Jason Lotay (UCL) Abstract: The goal will be to present a paper by Brendle and Kapouleas which modifies the gluing construction for Ricciflat metrics on a 4manifold (the K3 surface) known as the Kummer construction, described in Eleonora's talk on 1 March. The original motivation of the paper was to try to produce the first example of a compact Ricciflat metric with full holonomy, which in particular would be the first compact nonKaehler Ricciflat 4manifold. However, the end result is not a Ricciflat metric, but instead an ancient solution to Ricci flow. I will explain the apparent obstructions to the Ricciflat gluing problem and the modification required to obtain the solution to Ricci flow. 
Wed 9 December 2015 14:0016:00 UCL Maths Department Room 707 
H�lder continuity of tangent cones of limit spaces Speaker: Reto Buzano (M�ller) (QMUL) Abstract: In this talk, we will focus on Colding and Naber's result that tangent cones of limit spaces of manifolds with lower bounds on the Ricci curvature vary H�lder continuously along geodesics. This will follow from the H�lder continuity of the geometry of small balls with the same radius in smooth manifolds. All results can be found in http://arxiv.org/abs/1102.5003  the aim is to give a comprehensive overview of the most important parts of this paper. 
Wed 2 December 2015 14:0016:00 UCL Maths Department Room 707 
Almost volume cones and almost metric cone and the size of the singular set Speaker: Felix Schulze (UCL) Abstract: In this talk we will discuss that almost volume cones are almost metric cones and discuss the structure and the size of the limiting singular set. 
Wed 4 November 2015 14:0016:00 UCL Maths Department Room 707 
Almost rigidity: volume convergence Speaker: Yong Wei (UCL) Abstract: This talk will focus on the volume convergence part of CheegerColding theory. 
Wed 28 October 2015 14:0016:00 UCL Maths Department Room 707 
Almost rigidity: the almost splitting theorem Speaker: Yang Li (LSGNT) Abstract: This talk will be mainly about the almost splitting theorem (and depending on time I may or may not talk about the volume convergence). 
Wed 21 October 2015 14:0016:00 UCL Maths Department Room 500 
Introduction to CheegerColding theory Speaker: Panagiotis Gianniotis (UCL) and Jason Lotay (UCL) Abstract: In this talk we will first discuss the ChengYau gradient estimate, before starting on CheegerColding theory, including quantitative maximum principles, rigidity and almost rigidity, and the structure of limit spaces. 
Wed 14 October 2015 14:0016:00 UCL Maths Department Room 707 
Introduction to spaces with lower Ricci curvature bounds Speaker: Panagiotis Gianniotis (UCL) Abstract: In this talk I will survey some of the basic results in Riemannian Geometry which will form the building blocks for the study of limits of spaces with Ricci curvature bounded below. In particular, I will discuss the Bochner formula, volume and Laplacian comparision theorems, rigidity, Gromov's compactness theorem, the strong maximum principle and the splitting theorem. 
Wed 3 June 2015 14:0016:00 UCL Medical Sciences G46 HO Schild Pharmacology Lecture Theatre 
Monopole moduli spaces and metrics (Part 4)  The AtiyahHitchin Proposition Speaker: Karsten Fritzsch Abstract: In this part of our mini lecture series on magnetic monopoles, I will focus on a proposition by Atiyah and Hitchin concerning a type of asymptotic decomposition of monopoles. This proposition was already stated in the last part of this series and it was explained that it can be regarded as a starting point for a route towards a compactification of the moduli space of magnetic monopoles. In this part, I will go into the details of the proof of this proposition and in particular explain the convergence results of Uhlenbeck leading to this proposition. 
Wed 27 May 2015 14:0016:00 UCL Medical Sciences G46 HO Schild Pharmacology Lecture Theatre 
The KaehlerRicci flow on Kaehler surfaces and MMP Speaker: Eleonora di Nezza (Imperial) Abstract: It was recently proposed by Song and Tian a conjectural picture that relates the KaehlerRicci flow (KRF) to MMP (Minimal Model Program) with scaling. Although not so much is known in high dimension, much is understood about the KRF in the case of Kaehler surfaces. We will describe the behavior of the KRF on Kaehler surfaces and how it relates to the MMP. In particular, we will show how the KRF carries out the algebraic procedure of contracting (1)curves. (The results I will talk about are due to Song and Weinkove) 
Wed 20 May 2015 14:0016:00 UCL Medical Sciences G46 HO Schild Pharmacology Lecture Theatre 
Monopole moduli spaces and metrics (Part 3) Speaker: Michael Singer 
Wed 13 May 2015 14:0016:00 UCL Medical Sciences G46 HO Schild Pharmacology Lecture Theatre 
Monopole moduli spaces and metrics (Part 2) Speaker: Michael Singer 
Wed 6 May 2015 14:0016:00 UCL Medical Sciences G46 HO Schild Pharmacology Lecture Theatre 
Monopole moduli spaces and metrics (Part 1) Speaker: Michael Singer Abstract: We shall start with relevant definitions of monopoles, moduli spaces and the moduli space metrics. The conjectural structure of the asyptotic region of the moduli spaces will be discussed, and new progress on these metrics will be described. I will also aim to mention some important open problems within the first two weeks. After this, we will get technical with the analytic tools we use, including manifolds with corners, the relevant noncompact elliptic theory and so on. In particular I hope to explain why the use of manifolds with corners is natural and sensible for this problem. 
Wed 10 March 2015 11:001:00 UCL Taviton (16) Room 431 
An Introduction to the KaehlerRicci flow Speaker: Eleonora di Nezza (Imperial) Abstract: I will give an exposition of a number of wellknown results such as the maximal time of existence of the flow and the convergence on manifolds with negative and zero first Chern class. I will also discuss the regularizing properties of the KaehlerRicci flow. Finally, if time permits, I will show that the KaehlerRicci flow can be run from an arbitrary positive closed current, and that it is immediately smooth in a Zariski open subset of X. . 
Wed 25 February 2015 11:001:00 UCL Taviton (16) Room 431 
Tangent cones to twodimensional areaminimizing integral currents are unique Speaker: Tom Begley (Cambridge) Abstract: I will give an overview of the paper of Brian White of the same name. In this paper the author first reduces the problem of uniqueness of tangent cones to an 'epiperimetric' inequality. Then, for twodimensional areaminimizing currents, the inequality is proved by constructing explicit comparison surfaces using multiplevalued harmonic functions. As well as discussing the paper, I will start with a quick recap of the requisite geometric measure theory. 
Wed 11 February 2015 11:001:00 UCL Taviton (16) Room 431 
Heat Kernel and curvature bounds in Ricci flows with bounded scalar curvature (Part II) Speaker: Yong Wei Abstract: I will talk about the results in sections 67 of the paper "Heat Kernel and curvature bounds in Ricci flows with bounded scalar curvature" by Richard Bamler and Qi Zhang (arXiv:1501.01291). By assuming the scalar curvature is bounded along the Ricci flow, they proved the backward pseudolocality theorem which can be coupled with Perelman's forward pseudolocality theorem to deduce a stronger \epsilonregularity theorem for Ricci flow. As an application, they derived a uniform L^2bound for the Riemannian curvature in 4dimensional Ricci flow with uniformly bounded scalar curvature and show that such flow converges to an orbifold at a singularity. 
Wed 4 February 2015 11:001:00 UCL Drayton House Room B04 
Mean value inequalities and heat kernel bounds for the Ricci flow Speaker: Panagiotis Gianniotis Abstract: In their recent paper : "Heat Kernel and curvature bounds in Ricci flows with bounded scalar curvature" Richard Bamler and Qi Zhang analyse Ricci flows in which there is a bound on the scalar curvature. The ultimate goal of this work is to understand the possible singular behaviour of a Ricci flow when the scalar curvature remains bounded, and find situations that this singular behaviour can be excluded. I will talk about the first part of their paper, focusing on the results on Sections 35, in which they prove a distance distortion estimate (answering a question of Hamilton), construct good cutoff functions and prove several mean value inequalities for solutions of the heat and conjugate heat equations. These results finally lead to Gaussian bounds for heat kernels. 
Wed 28 January 2015 1:003:00 UCL 25 Gordon Street Room 707 
Asymptotic Rigidity of Selfshrinkers in Mean Curvature Flow Speaker: Lu Wang (Imperial) Abstract: In this talk, we discuss uniqueness of selfshrinkers with prescribed asymptotic behavior at infinity. The main tool is the Carleman type estimates. 
Wed 3 December 2014 1:303:00 UCL 25 Gordon Street Room 707 
Hyperbolic AlexandrovFenchel inequality Speaker: Yong Wei Abstract: I will present one work in my Phd thesis. For any 2convex and starshaped hypersurface in hyperbolic space, we prove a sharp AlexandrovFenchel type inequality involving the 2nd mean curvature integral and area of the hypersurface. I will start the talk with the motivation of the problem, including an introduction of isoperimetric and AlexandrovFenchel inequality in Euclidean space with the recent new proof and applications. Then I state our main result, recent progress and some open problems. Finally, I will give an overview of the proof: in the strictly 2convex case, the proof relies on an application of Gerhardt's convergence result of inverse mean curvature flow for strictly meanconvex hypersurfaces in hyperbolic space, and sharp Sobolev inequalities on sphere; in the general 2convex case, the proof involves an approximation argument. 
Wed 26 November 2014 1:003:00 UCL 25 Gordon Street Room 707 
Eleven dimensional supergravity equations on edge manifolds Speaker: Xuwen Zhu (MIT) Abstract: We consider the eleven dimensional supergravity equations on B^7xS^4 considered as an edge manifold. We compute the indicial roots of the linearized equations using the Hoge decomposition, and construct a realvalued generalized inverse using different behavior of spherical eigenvalues. We prove that all the solutions near the FreundRubin solution are prescribed by three pairs of data on the boundary 6sphere. 
Wed 19 November 2014 1:003:00 UCL 25 Gordon Street Room 707 
Uniqueness of Lawlor necks Speaker: Jason Lotay Abstract: I will discuss the paper by ImagiJoyceOliveira dos Santos on uniqueness of special Lagrangians and Lagrangian selfexpanders asymptotic to transverse pairs of planes. This will use the material on Fukaya categories discussed by Jonny Evans in the Symplectic Working Group Seminar on 18 Nov. 
Wed 12 November 2014 1:003:00 UCL 25 Gordon Street Room 707 
Shorttime existence of Lagrangian Mean Curvature Flow Speakers: Tom Begley and Kim Moore Abstract: We will present recent work on the shorttime existence of Lagrangian mean curvature flow with nonsmooth initial condition. Specifically we are able to show that given a smooth Lagrangian submanifold with a finite number of isolated singularities, each asymptotic to a pair of transversally intersecting Lagrangian planes P_1 and P_2 such that neither P_1 + P_2 or P_1  P_2 are area minimising, there exists a smooth Lagrangian mean curvature flow existing for a short time, and attaining the initial condition in the sense of varifolds as t goes to 0, and smoothly locally away from singularities. We will give an overview of the proof, which relies on a dynamic stability result for selfexpanders, a monotonicity formula for the selfexpander equation and the local regularity theorem of Brian White. 
Wed 29 October 2014 12:302:00 UCL 25 Gordon Street Room D103 
Results on the Ricci flow on manifolds with boundary Speaker: Panagiotis Gianniotis Abstract: Despite the great progress in the study of the Ricci flow on complete manifolds, the behaviour of the flow on manifolds with boundary remains a mystery. In this talk I will begin with an overview of past work on this problem, and describe the main difficulties it poses. Then, I will show that augmenting the Ricci flow with appropriate boundary conditions, one obtains local existence and uniqueness of the flow, starting from an arbitrary Riemannian manifold with boundary. I will also describe how these boundary conditions allow derivative estimates similar to Shi's to hold up to the boundary, although the maximum principle arguments that are typically used to obtain such estimates don't seem to be applicable. As a consequence we obtain a compactness result for sequences of Ricci flows and a continuation principle. I will finish the talk with a discussion on some open problems and questions. 
Wed 22 October 2014 12:002:00 UCL 25 Gordon Street Room 706 (121) Room 707 (12) 
Layer Potential Operators for Two Touching Domains in R^{n} Speaker: Karsten Fritzsch Abstract: So far, no special framework for the study of layer potential operators (or similar operators) on manifolds with corners has been developed even though both approaches, the method of layer potentials and the calculus of conormal distributions on manifolds with corners, have been proven to be very successful. In this talk, I will demonstrate in two important special cases that the geometric viewpoint of singular geometric analysis leads to a feasible approach to the method of layer potentials: I will solve the Dirichlet and Neumann problems for Laplace's equation on the halfspace in R^{n} in spaces of functions having certain (though very general) asymptotics and then move on to study the more singular situation of two touching domains in R^{n}. Using the PushForward Theorem, on the one hand I will show that the relations between the layer potential operators and their boundary counterparts continue to hold in the singular setting, and on the other hand establish mapping properties of the layer potential operators between spaces of functions with asymptotics. We can improve these by using a local splitting of certain fibrations which arise when applying the PushForward Theorem. In the first half of the talk, I will introduce and discuss the background material, including the method of layer potentials, polyhomogeneity and the PushForward Theorem, and the b and ?calculi of pseudodifferential operators. If time permits, I will end the talk by sketching the connection to the plasmonic eigenvalue problem on touching domains. 
Wed 8 October 2014 11:001:00 UCL 25 Gordon Street Room 706 
Lagrangian mean curvature flow and symplectic topology Speaker: Jason Lotay Abstract: I will discuss aspects of Dominic Joyce's recent preprint in which he conjectures modified versions of the ThomasYau conjecture, linking a notion of stability arising in symplectic topology with convergence of Lagrangian mean curvature flow. I will focus on the more concrete parts of his theory and its ramifications for the study of the flow. I will start with an introduction and review of Lagrangian mean curvature flow. 
Tues 1 Apr 2014 11:001:00 UCL 25 Gordon Street Room 706 
Finitetime singularities of Lagrangian mean curvature flow (part 1) Speaker: Felix Schulze Abstract: I will discuss some further details from the paper on the zeroMaslov class case for singularities in Lagrangian MCF by A. Neves. 
Wed 12 Mar 2014 11:301:30 KCL Strand Building Room S4.29 
Singularities of Lagrangian mean curvature flow: zeroMaslov class case Speaker: Kim Moore Abstract: I will talk about the paper of the same name by A. Neves. 
Wed 5 Mar 2014 12:0014:00 KCL Strand Building Room S4.36 
Introduction to Lagrangian mean curvature flow (part 2) Speaker: Jason Lotay Abstract: I will continue to describe some of the basics of Lagrangian mean curvature flow. In particular I will prove that it exists, discuss some examples and describe some more of the known results in the area. Much of what I say is found in my paper with Pacini, a paper by Thomas and Yau, the work of Schoen and Wolfson and in the survey by Neves. 
Wed 26 Feb 2014 12:0014:00 KCL Strand Building Room S4.36 
Introduction to Lagrangian mean curvature flow (part 1) Speaker: Jason Lotay Abstract: I will describe some of the basics of Lagrangian mean curvature flow. In particular I will describe what it is, the relevant parts of symplectic topology required and what the goal of the flow is. I will also try to survey some of the known results in the area. Much of what I say is found in my paper with Pacini, a paper by Thomas and Yau, the work of Schoen and Wolfson and in the survey by Neves. 
Wed 5 Feb 2014 12:0014:00 KCL Strand Building Room S4.36 
A local regularity theorem for mean curvature flow (part 2) Speaker: Tom Begley Abstract: I will continue to discuss the paper by Brian White of the same name. 
Wed 29 Jan 2014 12:0013:30 KCL Strand Building Room S4.36 
A local regularity theorem for mean curvature flow (part 1) Speaker: Tom Begley Abstract: I will discuss the paper by Brian White of the same name. 
Wed 22 Jan 2014 13:0015:00 Birkbeck Torrington Square Room 254 
Introduction to mean curvature flow (part 2) Speaker: Felix Schulze 
Wed 15 Jan 2014 13:0015:00 Birkbeck Torrington Square Room 254 
Introduction to mean curvature flow (part 1) Speaker: Felix Schulze 
