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Let $(M_j \mid j \in \mathbf{N})$ be a sequence of compact minimal surfaces in the unit ball $B \subset \mathbf{R}^3$, with boundaries $\partial M_j \subset \partial B$. Assume that the sequence converges to the horizontal plane $\mathbf{R}^2 \times \{ 0 \}$ with multiplicity $Q \geq 2$: \begin{equation} \lvert M_j \rvert \to Q \cdot \lvert \mathbf{R}^2 \times \{ 0 \} \rvert \quad \text{ as $j \to \infty$} \end{equation} in the varifold topology. Note that no bound for the Morse index or genus of the surfaces is assumed: $\mathrm{genus} \, M_j \to \infty$ and $\mathrm{index} \, M_j \to \infty$ is not forbidden in principle.

Question. Does the theory developed by Colding and Minicozzi give any further information about the convergence? If not, what kind of sheeting theorem is available when a uniform bound is assumed for the genus?

My (extremely limited) understanding of their work is that it gives decomposition results. Loosely I've heard the results described as stating that minimal surfaces can be decomposed into portions that resemble catenoidal necks, multi-valued graphs modelled on helicoids and single-valued graphs. (I don't actually know how accurate this is, even on a heuristic level.)

I would imagine that when there is a uniform bound like \begin{equation} \mathrm{genus} \, M_j \leq C \quad \text{ for all $j$}, \end{equation} then this could be applied to give a kind of sheeting theorem—perhaps multivalued—, valid away from the points where the necks concentrate. If the genus goes to infinity then this could not hold, but perhaps some other conclusions could be drawn on the sequence.

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    $\begingroup$ Without any topological assumption their work gives you nothing (as necks could, in principle, concentrate everywhere). Even with a genus bound, their work is only going to give information if the sequence is "global" in the sense of their papers (i.e. rather than having a fixed ball the boundaries lie in balls of radius tending to infinity). You should also keep in mind that one can have necks without genus (e.g. in the catenoid or Riemann examples). $\endgroup$
    – RBega2
    Commented Oct 21, 2021 at 21:24
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    $\begingroup$ Shoot, I always forget about this. What is the right way of formalising a bound on the topology: something like $\mathrm{genus} \, M_j + \mathrm{rank} \, \pi_1 (M_j) \leq C$? By the way, I'm surprised by what you explain about the sequence needing to be "global". I assumed that---with the topology bound---a sheeting theorem would be available even in this "local" setting. $\endgroup$
    – Leo Moos
    Commented Oct 22, 2021 at 9:30
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    $\begingroup$ Actually, reading your question more carefully, I realize you are assuming the convergence is with finite multiplicity. In this case, one should be able to use a result of Ilmanen (which is related to Colding Minicozzi's ideas) to get (under uniform genus bounds and some assumptions on boundaries) a uniform total curvature bound -- Page 32 of people.math.ethz.ch/~ilmanen/papers/notes.ps. This is then a classical removable singularities picture (as described later in the notes). $\endgroup$
    – RBega2
    Commented Oct 22, 2021 at 22:42
  • $\begingroup$ I've taken a look at the notes that you linked to, thanks! I still need some time to translate the arguments to the minimal setting, because I expected that the argument would be a bit simpler in this setting, e.g. by resorting to a blow-up argument. Could you confirm one thing: 'helicoid-like' portions can't actually appear when the mass is bounded, correct? $\endgroup$
    – Leo Moos
    Commented Oct 24, 2021 at 9:52
  • $\begingroup$ Yes assuming you are restricted to embedded surfaces a uniform area bound together with simple connectedness has a sheeting property. This is actually a result of Schoen and Simon (supposedly proved in degruyter.com/document/doi/10.1515/9781400881437-007/html) though I'll admit to never reading that paper. $\endgroup$
    – RBega2
    Commented Oct 24, 2021 at 12:57

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