arXiv subjects

Jesse Madnick

Publications and source records attributed to Jesse Madnick.

At least 19 recordsLinked to original sources

arXiv2026

Montel's theorem and tautness in calibrated geometry

We relate the hyperbolicity of a calibrated manifold $(X, \phi)$ to the analytic properties of the space of Smith immersions $\mathrm{SmIm}(B^k, X)$ from the Poincare $k$-ball into $X$. In particular, we establish the following calibrated analogue of a theorem of Royden: if $X$ is $\phi$-replete, then $R_\phi$- and $K_\phi$-hyperbolicity coincide, and either implies the equicontinuity of $\mathrm{SmIm}(B^k, X)$ with respect to the $\phi$-distance. This yields a Montel theorem for compact $\phi$-replete calibrated manifolds as an immediate corollary. Our primary technical tool is a new Schwarz lemma for Smith immersions from $B^k$ into $X$, which is of independent interest. In a similar spirit, we also prove a calibrated analogue of Kiernan's theorem to the effect that the $K_\phi$-hyperbolicity of $X$ is almost equivalent to $\mathrm{SmIm}(B^k, X)$ being a normal family. Finally, we prove that bounded domains in flat euclidean space are $R_\phi$-hyperbolic for any calibration $\phi$, and we investigate the hyperbolicity of products and discrete quotients.

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arXiv2026

The Morse index of constant curvature 2-spheres

In the round $N$-sphere, we calculate the Morse index and nullity of all immersed minimal 2-spheres having constant Gauss curvature. We also obtain bounds on the stability index of the associative cone in $R^7$ whose link is the Boruvka sphere in $S^6$.

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arXiv2025

Holomorphicity of parabolic stable minimal surfaces of high codimension

A classical theorem of Micallef says that if $F \colon (Σ, g) \to \mathbb{R}^4$ is a stable minimal immersion of an oriented $2$-dimensional complete Riemannian manifold (that is parabolic) into $\mathbb{R}^4$, it is necessarily holomorphic with respect to some parallel orthogonal complex structure on $\mathbb{R}^4$. We generalize this theorem by replacing $\mathbb{R}^4$ with $\mathbb{R}^{2 + 2k}$ for any codimension $2k$, under the additional hypothesis that the normal bundle $N Σ$ is equipped with a complex structure that is compatible with the induced metric and parallel with respect to the induced connection. This is a necessary assumption for such a theorem to hold, and it is automatically satisfied in the classical case $k=1$. We also briefly discuss possible further generalizations of such a result to other calibrations and to Smith maps.

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arXiv2025

Gauge theory on $T^*CP^2$: explicit Sp(2)-instantons, HYM connections, and Spin(7)-instantons

We construct and classify $SU(3)$-invariant primitive Hermitian Yang-Mills connections and $Sp(2)$-instantons with gauge groups $S = S^1$ and $S = SO(3)$ over the Calabi manifold $X = T^*CP^2$, the unique non-flat, complete, cohomogeneity-one hyperkahler 8-manifold. Moreover, in the case of $S = S^1$, we also classify the $SU(3)$-invariant $Spin(7)$-instantons over $X$ in the following sense. Letting $Φ_I$, $Φ_J$, $Φ_K$ denote the $Spin(7)$-structures on $X$ induced from the complex structures $I$, $J$, $K$ in the hyperkahler triple, we prove that on each invariant $S^1$-bundle $\widetilde{E}_k \to X$, $k \in \mathbb{Z}$, the space of invariant $Spin(7)$-instantons with respect to $Φ_L$ forms a one-parameter family modulo gauge. Moreover, every pair of one-parameter families of $Φ_I$-, $Φ_J$-, and $Φ_K$-$Spin(7)$-instantons intersects only at the unique invariant $Sp(2)$-instanton on $\widetilde{E}_k$, which is non-flat when $k \neq 0$.

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arXiv2025

Hyperbolicity and Schwarz Lemmas in Calibrated Geometry

This paper has two main objectives. First, for an arbitrary calibrated manifold $(X,\phi)$, we define notions of $R_\phi$-hyperbolicity and $\phi$-hyperbolicity, which respectively generalize the notions of Kobayashi and Brody hyperbolicity from complex geometry. To make sense of the former, we introduce the "KR $\phi$-metric," a decreasing Finsler pseudo-metric that specializes to the Kobayashi-Royden pseudo-metric in the Kahler case. We prove that $R_\phi$-hyperbolicity implies $\phi$-hyperbolicity, and give examples showing that the converse fails in general. Moreover, for constant-coefficient, inner Mobius rigid calibrations $\phi$ in $\mathbb{R}^n$, we completely characterize those domains that are $\phi$-hyperbolic. Second, we derive a Schwarz lemma for Smith immersions (a.k.a. conformal $\phi$-curves) into an arbitrary calibrated manifold $(X, \phi)$, thereby extending the Schwarz lemma for holomorphic curves into Kahler manifolds. The relevant Bochner formula features the "$\phi$-sectional curvature," a new notion that includes both the scalar and holomorphic sectional curvatures as special cases. As an application, we prove that calibrated geometries with $\phi$-sectional curvature bounded above by a negative constant are $R_\phi$-hyperbolic, generalizing the corresponding result from complex geometry. As another application, we calculate the KR $\phi$-metric of real, complex, and quaternionic hyperbolic spaces equipped with their natural calibrations.

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arXiv2024

On Sp(n)-Instantons and the Fourier-Mukai Transform of Complex Lagrangians

The real Fourier-Mukai (RFM) transform relates calibrated graphs to so-called "deformed instantons" on Hermitian line bundles. We show that under the RFM transform, complex Lagrangian graphs in $R^{2n} \times T^{2n}$ correspond to Sp($n$)-instantons over $R^{2n} \times (T^{2n})^*$. In other words, the deformed Sp($n$)-instanton equation coincides with the usual Sp($n$)-instanton equation. Motivated by this observation, we study Sp($n$)-instantons on hyperkahler manifolds $X^{4n}$, with an emphasis on conical singularities. First, when $X = C(M)$ is a hyperkahler cone, we relate Sp($n$)-instantons on $X$ to tri-contact instantons on the 3-Sasakian link $M$ and consider various dimensional reductions. Second, when $X$ is an asymptotically conical (AC) hyperkahler manifold of rate $ν\leq -\frac{2}{3}(2n+1)$, we prove a Lewis-type theorem to the following effect: If the set of AC Sp($n$)-instantons is non-empty, then every AC Hermitian Yang-Mills connection over $X$ with sufficiently fast decay at infinity is an Sp($n$)-instanton.

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arXiv2024

Calibrated Geometry in Hyperkahler Cones, 3-Sasakian Manifolds, and Twistor Spaces

We systematically study calibrated geometry in hyperkähler cones $C^{4n+4}$, their 3-Sasakian links $M^{4n+3}$, and the corresponding twistor spaces $Z^{4n+2}$, emphasizing the relationships between submanifold geometries in various spaces. Our analysis emphasizes the role played by a canonical $\mathrm{Sp}(n)\mathrm{U}(1)$-structure $γ$ on the twistor space $Z$. We observe that $\mathrm{Re}(e^{- i θ} γ)$ is an $S^1$-family of semi-calibrations, and make a detailed study of their associated calibrated geometries. As an application, we obtain new characterizations of complex Lagrangian and complex isotropic cones in hyperkähler cones, generalizing a result of Ejiri and Tsukada. We also generalize a theorem of Storm on submanifolds of twistor spaces that are Lagrangian with respect to both the Kähler-Einstein and nearly-Kähler structures.

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arXiv2023

The Morse index of quartic minimal hypersurfaces

The homogeneous minimal hypersurfaces in $S^n$ have $g = 1,2,3,4$, or $6$ distinct (constant) principal curvatures. While the Morse index and nullity have been calculated for all such hypersurfaces having $g = 1,2,3$, it has remained an open problem to compute these quantities for any of those with $g = 4$ or $6$. In this paper, we calculate the Morse index and nullity of two homogeneous minimal hypersurfaces in $S^n$ with $g = 4$. Moreover, we observe that their Laplace spectra contain irrational eigenvalues that are not expressible in radicals.

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arXiv2023

Cohomogeneity-One Lagrangian Mean Curvature Flow

We study mean curvature flow of Lagrangians in $\mathbb{C}^n$ that are cohomogeneity-one with respect to a compact Lie group $G \leq \mathrm{SU}(n)$ acting linearly on $\mathbb{C}^n$. Each such Lagrangian necessarily lies in a level set $μ^{-1}(ξ)$ of the standard moment map $μ\colon \mathbb{C}^n \to \mathfrak{g}^*$, and mean curvature flow preserves this containment. We classify all cohomogeneity-one self-similarly shrinking, expanding and translating solutions to the flow, as well as cohomogeneity-one smooth special Lagrangians lying in $μ^{-1}(0)$. Restricting to the case of almost-calibrated flows in the zero level set $μ^{-1}(0)$, we classify finite-time singularities, explicitly describing the Type I and Type II blowup models. Finally, given any cohomogeneity-one special Lagrangian in $μ^{-1}(0)$, we show it occurs as the Type II blowup model of a Lagrangian MCF singularity. Throughout, we give explicit examples of suitable group actions, including a complete list in the case of $G$ simple. This yields infinitely many new examples of shrinking and expanding solitons for Lagrangian MCF, as well as infinitely many new singularity models.

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arXiv2023

A Spinorial Hopf Differential for Associative Submanifolds

Given a CMC surface in $R^3$, its traceless second fundamental form can be viewed as a holomorphic section called the Hopf differential. By analogy, we show that for an associative submanifold of a 7-manifold $M^7$ with $G_2$-structure, its traceless second fundamental form can be viewed as a twisted spinor. Moreover, if $M$ is $R^7$, $T^7$, or $S^7$ with the standard $G_2$-structure, then this twisted spinor is harmonic. Consequently, every non-totally-geodesic associative 3-fold in $R^7$, $T^7$, and $S^7$ admits non-vanishing harmonic twisted spinors. Analogous results hold for special Lagrangians in $R^6$ and $T^6$, coassociative 4-folds in $R^7$ and $T^7$, and Cayley 4-folds in $R^8$ and $T^8$.

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arXiv2023

A variational characterization of calibrated submanifolds

Let $M$ be a fixed compact oriented embedded submanifold of a manifold $\overline{M}$. Consider the volume $\mathcal{V} (\overline{g}) = \int_M \mathsf{vol}_{(M, g)}$ as a functional of the ambient metric $\overline{g}$ on $\overline{M}$, where $g = \overline{g}|_M$. We show that $\overline{g}$ is a critical point of $\mathcal{V}$ with respect to a special class of variations of $\overline{g}$, obtained by varying a calibration $μ$ on $\overline{M}$ in a particular way, if and only if $M$ is calibrated by $μ$. We do not assume that the calibration is closed. We prove this for almost complex, associative, coassociative, and Cayley calibrations, generalizing earlier work of Arezzo-Sun in the almost Kähler case. The Cayley case turns out to be particularly interesting, as it behaves quite differently from the others. We also apply these results to obtain a variational characterization of Smith maps.

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arXiv2022

Associative Submanifolds of Squashed 3-Sasakian Manifolds

Every compact 3-Sasakian 7-manifold $M$ admits a canonical 2-parameter family of co-closed $\text{G}_2$-structures $φ_{a,b}$ for $a,b > 0$, as well as a foliation by $φ_{a,b}$-associative 3-folds whose leaf space $X$ is a positive quaternion-Kähler 4-orbifold. We prove that associative 3-folds in $(M,φ_{a,b})$ that are ruled by a certain type of geodesic are in correspondence with pseudo-holomorphic curves in the almost-complex 8-manifold $Z \times S^2$, where $Z$ is the twistor space of $X$ equipped with its strict nearly-Kähler structure. As an application, we construct infinitely many topological types of non-trivial, compact associative 3-folds in the squashed 7-spheres $(S^7, φ_{a,b})$ and squashed exceptional Aloff-Wallach spaces $(N_{1,1}, φ_{a,b})$. Topologically, our examples are circle bundles over a genus $g$ surface, for any $g \geq 0$.

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arXiv2021

The Second Variation for Null-Torsion Holomorphic Curves in the 6-Sphere

In the round 6-sphere, null-torsion holomorphic curves are fundamental examples of minimal surfaces. This class of minimal surfaces is quite rich: By a theorem of Bryant, extended by Rowland, every closed Riemann surface may be conformally embedded in the round 6-sphere as a null-torsion holomorphic curve. In this work, we study the second variation of area for compact null-torsion holomorphic curves $Σ$ of genus $g$ and area $4πd$, focusing on the spectrum of the Jacobi operator. We show that if $g \leq 6$, then the multiplicity of the lowest eigenvalue $λ_1 = -2$ is exactly equal to $4d$. Moreover, for any genus, we show that the nullity is at least $2d + 2 - 2g$. These results are likely to have implications for the deformation theory of asymptotically conical associative $3$-folds in $\mathbb{R}^7$, as studied by Lotay.

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arXiv2021

Bubble Tree Convergence of Conformally Cross Product Preserving Maps

We study a class of weakly conformal $3$-harmonic maps, called associative Smith maps, from $3$-manifolds into $7$-manifolds that parametrize associative $3$-folds in Riemannian $7$-manifolds equipped with $\mathrm{G}_2$-structures. Associative Smith maps are solutions of a conformally invariant nonlinear first order PDE system, called the Smith equation, that may be viewed as a $\mathrm{G}_2$-analogue of the Cauchy-Riemann system for $J$-holomorphic curves. In this paper, we show that associative Smith maps enjoy many of the same analytic properties as $J$-holomorphic curves in symplectic geometry. In particular, we prove: (i) an interior regularity theorem, (ii) a removable singularity result, (iii) an energy gap result, and (iv) a mean-value inequality. While our approach is informed by the holomorphic curve case, a number of nontrivial extensions are involved, primarily due to the degeneracy of the Smith equation. At the heart of above results is an $\varepsilon$-regularity theorem that gives quantitative $C^{1,β}$-regularity of $W^{1,3}$ associative Smith maps under a smallness assumption on the $3$-energy. The proof combines previous work on weakly $3$-harmonic maps and the observation that the associative Smith equation demonstrates a certain "compensation phenomenon" that shows up in many other geometric PDEs. Combining these analytical properties and the conformal invariance of the Smith equation, we explain how sequences of associative Smith maps with bounded $3$-energy may be conformally rescaled to yield bubble trees of such maps. When the $\mathrm{G}_2$-structure is closed, we prove that both the $3$-energy and the homotopy are preserved in the bubble tree limit. This result may be regarded as an associative analogue of Gromov's Compactness Theorem in symplectic geometry.

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arXiv2021

Free-Boundary Problems for Holomorphic Curves in the 6-Sphere

We remark on two different free-boundary problems for holomorphic curves in nearly-Kähler 6-manifolds. First, we observe that a holomorphic curve in a geodesic ball $B$ of the round 6-sphere that meets $\partial B$ orthogonally must be totally geodesic. Consequently, we obtain rigidity results for reflection-invariant holomorphic curves in $\mathbb{S}^6$ and associative cones in $\mathbb{R}^7$. Second, we consider holomorphic curves with boundary on a Lagrangian submanifold in a strict nearly-Kähler 6-manifold. By deriving a suitable second variation formula for area, we observe a topological lower bound on the Morse index. In both settings, our methods are complex-geometric, closely following arguments of Fraser-Schoen and Chen-Fraser.

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arXiv2020

The Mean Curvature of Special Lagrangian 3-folds in SU(3)-Structures with Torsion

We derive formulas for the mean curvature of special Lagrangian 3-folds in the general case where the ambient 6-manifold has intrinsic torsion. Consequently, we are able to characterize those SU(3)-structures for which every special Lagrangian 3-fold is a minimal submanifold. In the process, we obtain an obstruction to the local existence of special Lagrangian 3-folds.

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arXiv2020

Free-Boundary Minimal Surfaces of Constant Kahler Angle in Complex Space Forms

In real space forms, Fraser and Schoen proved that a free-boundary minimal disk in a geodesic ball is totally geodesic. In this note, we consider free-boundary minimal surfaces $Σ$ (of any genus) in geodesic balls of complex space forms. In $\mathbb{CP}^2$, $\mathbb{C}^2$ and $\mathbb{CH}^2$, we show that if $Σ$ is Lagrangian, then $Σ$ is totally geodesic. In $\mathbb{CP}^n$, $\mathbb{C}^n$ and $\mathbb{CH}^n$ for $n \geq 2$, we show that if $Σ$ has Kähler angle $π/2$, then $Σ$ is superminimal.

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arXiv2020

Associative Submanifolds of the Berger Space

We study associative submanifolds of the Berger space SO(5)/SO(3) endowed with its homogeneous nearly-parallel G2-structure. We focus on two geometrically interesting classes: the ruled associatives, and the associatives with special Gauss map. We show that the associative submanifolds ruled by a certain special type of geodesic are in correspondence with pseudo-holomorphic curves in $Gr_2^+(TS^4).$ Using this correspondence, together with a theorem of Bryant on superminimal surfaces in $S^4,$ we prove the existence of infinitely many topological types of compact immersed associative 3-folds in SO(5)/SO(3). An associative submanifold of the Berger space is said to have special Gauss map if its tangent spaces have non-trivial SO(3)-stabiliser. We classify the associative submanifolds with special Gauss map in the cases where the stabiliser contains an element of order greater than 2. In particular, we find several homogeneous examples of this type.

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