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Let me state my question in very loose terms to start, then give some details and restate it in more precise terms at the bottom.

Question. Given a regular minimal cone $\mathbf{C}$, can one set up a well-defined min-max problem between surfaces lying on either side?

Let $\mathbf{C}$ be an $n$-dimensional minimal cone in $\mathbf{R}^{n+1}$. Write $\Sigma = \mathbf{C} \cap \partial B$ for its link, which we assume to be embedded in the sphere. This divides the sphere into two halves, and we write \begin{equation} \partial B \setminus \Sigma = U_- \cup U_+. \end{equation}

Let $\Sigma_{\pm} \subset U_{\pm}$ be two embedded hypersurfaces, in the same homology class, and which lie close to $\Sigma$: \begin{equation} \mathrm{dist}(\Sigma_{\pm},\Sigma) \leq \delta \quad \text{ for some small $\delta > 0$.} \end{equation} Let moreover $M_{\pm}$ be two surfaces in $B$ with $\partial M_{\pm} = \Sigma_{\pm}$, for which we assume there exists an open subset $V \subset B$ so that \begin{equation} \mathrm{spt} \, \mathbf{C} \subset V \quad \text{and} \quad \partial V = M_- \cup M_+. \end{equation}

Consider families of currents $(M_t \mid -1 \leq t \leq 1)$ in the closure of $V$ with $M_{\pm 1} = M_{\pm}.$ We assume that they vary continuously with respect to the flat topology. If necessary, they may be assumed continuous in some finer topology. Perhaps additionally one ought to assume that their boundaries are all homologous: \begin{equation} [\partial M_{t}] = [\partial M_\pm] \quad \text{ for all $-1 \leq t \leq 1$.} \end{equation}

Then define the quantity \begin{equation} W = \inf \max_{-1 \leq t \leq 1} \lVert M_t \rVert, \end{equation} where the infimum is over all families of currents satisfying the hypotheses lined out above.

Question. Is this a well-defined min-max construction, in the sense that $W$ is realised by a free boundary minimal surface in $B$? When is it true $\lVert \mathbf{C} \rVert(B) = W$: always, sometimes, never?

Let me write down a few elementary thoughts, all made under the assumption that (some version of) the problem makes sense.

  • Variationally one could expect $\mathrm{index} \, T \leq 1$, including for perturbations of the boundary. Therefore $\mathbf{C} \neq T$ if the cone is unstable with respect to $C^1_c(B)$, it seems.

  • If $\delta > 0$ is too large, say large enough that $\Sigma_{\pm} = \partial B_r(p_\pm) \cap \partial B$ for some small radius $r > 0$ and two points $p_\pm \in \partial B$ is legal, then $W = \omega_n$ and is realised by an equatorial disc.

  • The hypothesis that $M_t \subset \overline{V}$ is crucial. Otherwise one could shrink $M_{\pm}$ down to small discs, in a way that would make $W = \max \{ \lVert M_{-} \rVert, \lVert M_{+} \rVert \}$ likely. Perhaps additionally $V$ would need to be mean convex?

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  • $\begingroup$ This paper should be relevant arxiv.org/pdf/2007.11560.pdf . I think that to ask such a question, one should first solve the (seemingly hard) problem of whether or not there is a stable cone that does not minimize area on either side. If so, then that cone is possibly min-max with respect to such a construction. See also these notes web.stanford.edu/~ochodosh/GAFestival2021.pdf for some discussion (section 4.2). $\endgroup$ Commented Aug 29, 2021 at 19:00
  • $\begingroup$ @OtisChodosh Thank you for your comment! I took a look at the paper and the notes, but I am having trouble seeing the precise connection. Would you mind elaborating? If I understood you correctly, the construction would not yield the cone when it is minimising, say $\mathbf{C}$ is the Simons cone $\mathbf{C}^{3,3}$ and $M_{\pm}$ are two nearby leaves. I am guessing you're suggesting a perturbation like in your paper, but would that continuously connect the two leaves? It seems to me you'd be perturbing away from $\mathbf{C}$ on either side, thus never 'crossing' the cone. $\endgroup$
    – Leo Moos
    Commented Aug 30, 2021 at 15:09
  • $\begingroup$ Sorry, it's a bit tenuous (and I am not sure I completely understand your setup). The interesting situation is if you can find a non-minimizing (but stable) cone. (Nobody knows if this exists; the $C^{1,5}$ Simons cone is non-minimizing on one side but minimizing on the other). If so, choose $M_\pm$ the minimizers on either side of $C$ with boundary $C\cap\partial B_1$. Now, try to min-max between $M_\pm$. Is $C$ the min-max surface? By the paper, any min-max surface has index + singularities $\leq 1$. This is why $C$ should be stable (note that an unstable cone has infinite index). $\endgroup$ Commented Aug 30, 2021 at 16:22
  • $\begingroup$ ... Of course, it is possible that some other index 1 surface (with no singularities) or a stable surface with a single singularity appears. But, it's hard to say without having an example of $C$. $\endgroup$ Commented Aug 30, 2021 at 16:22
  • $\begingroup$ Note that when $C$ is minimizing, a natural min-max procedure would be to try to sweep out between leaves of the Hardt-Simon foliation on both sides. I dont know what one can say about this, but perhaps the following paper is related (the connection is not immediately clear, just the idea is similar somehow): mathscinet.ams.org/mathscinet-getitem?mr=3356355 $\endgroup$ Commented Aug 30, 2021 at 16:24

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