We propose a weak formulation for the binormal curvature flow of curves in ${ℝ}^3$. This formulation is sufficiently broad to consider integral currents as initial data, and sufficiently strong for the weak-strong uniqueness property to hold, as long as self-intersections do not occur. We also prove a global existence theorem in that framework.

A description of the short time behavior of solutions of the Allen–Cahn equation with a smoothened additive noise is presented. The key result is that in the sharp interface limit solutions move according to motion by mean curvature with an additional stochastic forcing. This extends a similar result of Funaki [Acta Math. Sin (Engl. Ser.)15 (1999) 407–438] in spatial dimension n=2 to arbitrary dimensions.

In a crystalline algorithm, a tangential velocity is used implicitly. In this short note, it is specified for the case of evolving plane curves, and is characterized by using the intrinsic heat equation.

We survey recent work on local well-posedness results for parabolic equations and systems with rough initial data. The design of the function spaces is guided by tools and constructions from harmonic analysis, like maximal functions, square functions and Carleson measures. We construct solutions under virtually optimal scale invariant conditions on the initial data. Applications include BMO initial data for the harmonic map heat flow and the Ricci-DeTurck flow for initial metrics with small local...

Nous présentons la preuve de la conjecture de Poincaré, concernant les variétés compactes simplement connexes de dimension $3$, proposée par G. Perel’man. Elle repose sur l’étude de l’évolution de métriques riemanniennes sous le flot de la courbure de Ricci et sur les travaux antérieurs de R. Hamilton. Après une introduction aux techniques analytiques et géométriques développées par R. Hamilton, nous tentons de décrire la méthode de chirurgie métrique utilisée par G. Perel’man pour franchir les temps...

On étudie quelques équations complètement non linéaires issues de la géométrie conforme. Par une méthode de flot géométrique, on prouve l’existence des solutions. En utilisant ce résultat analytique, on obtient un théorème sur la topologie de la variété : soit $M$ une variété riemannienne compacte de dimension 3. S’il existe une metrique $g$ à courbure scalaire strictement positive telle que l’intégrale de la ${\sigma }_2$-courbure scalaire soit positive, alors $M$ est difféomorphe à un quotient de la sphere.

We show, using a direct variational approach, that the second boundary value problem for the Monge-Ampère equation in ${ℝ}^n$ with exponential non-linearity and target a convex body $P$ is solvable iff $0$ is the barycenter of $P.$ Combined with some toric geometry this confirms, in particular, the (generalized) Yau-Tian-Donaldson conjecture for toric log Fano varieties $(X,\Delta )$ saying that $(X,\Delta )$ admits a (singular) Kähler-Einstein metric iff it is K-stable in the algebro-geometric sense. We thus obtain a new proof and...

By exploiting Perelman’s pseudolocality theorem, we prove a new compactness theorem for Ricci flows. By optimising the theory in the two-dimensional case, and invoking the theory of quasiconformal maps, we establish a new existence theorem which generates a Ricci flow starting at an arbitrary incomplete metric, with Gauss curvature bounded above, on an arbitrary surface. The criterion we assert for well-posedness is that the flow should be complete for all positive times; our discussion of uniqueness...

We investigate a coupled system of the Ricci flow on a closed manifold $M$ with the harmonic map flow of a map $\phi$ from $M$ to some closed target manifold $N$,$$\frac{\partial }{\partial t}g=-2\mathrm{Rc}+2\alpha \nabla \phi \otimes \nabla \phi ,\frac{\partial }{\partial t}\phi ={\tau }_g\phi ,$$where $\alpha$ is a (possibly time-dependent) positive coupling constant. Surprisingly, the coupled system may be less singular than the Ricci flow or the harmonic map flow alone. In particular, we can always rule out energy concentration of $\phi$ a-priori by choosing $\alpha$ large enough. Moreover, it suffices to bound the curvature of $(M,g(t\left)\right)$ to also obtain control of ...

We consider a network in the Euclidean plane that consists of three distinct half-lines with common start points. From that network as initial condition, there exists a network that consists of three curves that all start at one point, where they form $120$ degree angles, and expands homothetically under curve shortening flow. We also prove uniqueness of these networks.

We present the general theory of barrier solutions in the sense of De Giorgi, and we consider different applications to ordinary and partial differential equations. We discuss, in particular, the case of second order geometric evolutions, where the barrier solutions turn out to be equivalent to the well-known viscosity solutions.

We show that the classical solution of the heat equation can be seen as the minimizer of a suitable functional defined in space-time. Using similar ideas, we introduce a functional $ℱ$ on the class of space-time tracks of moving hypersurfaces, and we study suitable minimization problems related with $ℱ$. We show some connections between minimizers of $ℱ$ and mean curvature flow.

In this paper, we consider some evolution equations of generalized Ricci curvature and generalized scalar curvature under the List’s flow. As applications, we obtain $L^2$-estimates for generalized scalar curvature and the first variational formulae for non-negative eigenvalues with respect to the Laplacian.

The linearized stability of stationary solutions for the surface diffusion flow with a triple junction is studied. We derive the second variation of the energy functional under the constraint that the enclosed areas are preserved and show a linearized stability criterion with the help of the $H^{-1}$-gradient flow structure of the evolution problem and the analysis of eigenvalues of a corresponding differential operator.