I am a bit confused about Theorem 2.16 in the book “A Course in Minimal Surfaces” by Colding and Minicozzi. The authors write that Theorem 2.16 was proved in this paper by Schoen and Simon in the more general setting of surfaces with quasiconformal Gauss map.

I looked at the paper of Schoen and Simon, but they prove a Holder estimate for the Gauss map. How can one get the curvature estimate in Colding-Minicozzi’s book from that Holder estimate?

Any help will be very much apreciated!

This is the statement of Theorem 2.16.

————————————————————————————————————————————

EDIT

Theorem 2.16: Let 0∈Σ⊂Br0=Br0(0)⊆R3 be an embedded simply connected minimal surface with ∂Σ⊂∂Br0. If μ>0 and either

(i)Area(Σ)≤μr20

or

(ii)∫Σ|A|2≤μ,

then for the connected component Σ′ of Br02∩Σ with 0∈Σ′ we have

(⋆)supΣ′|A|2≤Cr−20

for some C=C(μ).

I know that one cannot expect such a strong estimate for a general surface with quasiconformal Gauss map.For instance consider a cylinder S1×R. It has quasiconformal Gauss map because it has bounded (actually constant) mean curvature. Moreover it has linear area growth and thus in particular it satisfies (i) for large r0. But it does not satisfy (⋆).On the other hand from the paper of Schoen and Simon I would expect to derive a pointwise curvature estimate, but I don’t know how.

————————————————————————————————————————————

SECOND EDIT:A denotes the second fundamental form.

**Answer**

Theorem 2.16 (for embedded minimal disks) is implicit in Schoen-Simon. There are two steps. The first is that some area (or total curvature) bound on an extrinsic ball implies small total curvature on a sub-ball. This is the key point and it is this that is generalized to intrinsic balls here.

Schoen and Simon show that the area bound implies small total curvature on a sub-ball even for surfaces with quasi-conformal Gauss maps. The argument that gives this also implies a Holder estimate on the Gauss map.

The second part, which is true for minimal surfaces but not necessarily more generally, is that small total curvature implies a point-wise estimate. There are many ways to see this. The simplest is via the Choi-Schoen estimate. One could also see it from Schoen-Simon-Yau in this case since one also has area bounds.

**Attribution***Source : Link , Question Author : Math_tourist , Answer Author : minicozz*