Flat interior singularities for area almost-minimizing currents

TL;DR

This paper constructs examples of area almost-minimizing currents with flat singular sets that can be any closed, empty interior subset of a plane, demonstrating the sharpness of previous regularity results.

Contribution

It provides explicit constructions of almost-minimizing currents with prescribed flat singular sets, showing the limits of regularity results for such currents.

Findings

Constructed examples with flat singular sets containing any closed, empty interior subset.

Demonstrated sharpness of Bombieri's density result for almost-minimizing currents.

Extended understanding of the possible structure of singular sets in area almost-minimizing currents.

Abstract

The interior regularity of area-minimizing integral currents and semi-calibrated currents has been studied extensively in recent decades, with sharp dimension estimates established on their interior singular sets in any dimension and codimension. In stark contrast, the best result in this direction for general almost-minimizing integral currents is due to Bombieri in the 1980s, and demonstrates that the interior regular set is dense. The main results of this article show the sharpness of Bombieri's result by constructing two families of examples of area almost-minimizing integral currents whose flat singular sets contain any closed, empty interior subset $K$ of an $m$-dimensional plane in $\mathbb{R}^{m+n}$. The first family of examples are codimension one currents induced by a superposition of $C^{k,\alpha_*}$ graphs with $K$ contained in the boundary of their zero set. The second family of examples are two dimensional area almost-minimizing integral currents in $\mathbb{R}^4$ whose set of branching singularities contains $K$.