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Partial differential equations (PDEs): Existence and uniqueness, regularity, boundary conditions, linear and non-linear operators, stability, soliton theory, integrable PDEs, conservation laws, qualitative dynamics.

2 votes
1 answer
377 views

Longtime behaviour of the periodic KdV equation

I was wondering if anyone could give a heuristic (i.e. preferably non-technical) explanation of what is the expected longtime behavior of the periodic KdV equation. Recall the standard KdV equation …
Rbega's user avatar
  • 2,299
1 vote
1 answer
79 views

Finding singular "solutions" to the Dirichlet problem for Schrödinger operators that do not ...

Suppose that $\Omega\subset \mathbb{R}^n$ is a smooth open region and that $V:\Omega\to \mathbb{R}^+$ be a positive smooth function. Then we have a family of operators $$L_\epsilon =-\Delta -\epsilon …
Rbega's user avatar
  • 2,299
1 vote
Accepted

Partial $L^2$ control on (part of) the Hessian of a harmonic function.

Okay so I thought about this some more and I believe it is just a (really) straightforward application of the Poincare/Wirtinger inequality and the obvious way you would solve $u_{xy}=0$ classically. …
Rbega's user avatar
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1 vote
1 answer
391 views

Partial $L^2$ control on (part of) the Hessian of a harmonic function.

I have a simple little analysis question that I'm hoping is well known. Suppose $D=\lbrace(x,y): x^2+y^2<1\rbrace$ is the unit disk and that $u$ is a harmonic function on $D$. Suppose in addition th …
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  • 2,299
7 votes

PDEs as a tool in other domains in mathematics

How about Hodge theory. I.e. that each DeRham cohomology class of a smooth compact manifold has a harmonic representative (one has to of course choose a Riemannian metric to make sense of harmonic). T …
2 votes
0 answers
267 views

Finer properties of a sequence of harmonic functions

This was a question that arose for me when I was thinking about how one proves strong unique continuation for elliptic equations. I never could come up with a satisfactory answer. Background: When o …
Rbega's user avatar
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9 votes

Does Ricci flow with surgery come from sections of a smooth Riemannian manifold?

To build a little on what Agol said: For mean curvature flow of hypersurfaces, the analogous question is at least partially known to be true (sort of). The advantage of the mean curvature flow over …
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2 votes
1 answer
2k views

The normal derivative of the Green's function

I was wondering if anything was known about the following: Let $\mathbb{D}^2=\lbrace x^2+y^2< 1 \rbrace \subset \mathbb{R}^2$ be the open unit disk. Consider now the Green's functions $G(z; p)$ of t …
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3 votes
0 answers
318 views

Controlling the Second Eigenvalue of a Schrödinger Operator

Consider a bounded domain $\Omega$ (with smooth boundary) in some Riemannian $n$-manifold $M^n$. Let $L$ be the operator $$ L=\Delta+V $$ where $\Delta$ is the Laplace-beltrami operator on $M$ (so is …
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  • 2,299
3 votes
Accepted

Epsilon regularity for minimal surfaces in arbitrary Riemannian manifolds

The desired bound is correct (and in fact you get a fairly explicit value for $\epsilon$ of anything below $4\pi$) . A proof can be found in these beautiful notes of a course by Brian White (it's Th …
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