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<title>Neckpinch — Boundaries &amp; non-compact</title><link>https://neckpinch.com/topics/boundary/</link><description>New arXiv papers on boundaries &amp; non-compact, from Neckpinch</description>
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<item><title>Conjugate radius and parabolicity along the Ricci flow</title><link>https://neckpinch.com/papers/2611.03823/</link><guid isPermaLink="false">arxiv:2611.03823</guid><pubDate>Mon, 02 Nov 2026 00:00:00 GMT</pubDate><description>Chandan Kumar Mondal — We study the behaviour of the conjugate radius under the Ricci flow on complete noncompact manifolds. We show that if (Mⁿ,g(t))_(t∈[0,T]) is a complete Ricci flow with nonnegative scalar curvature at t=0, the initial metric is parabolic and not Ricci-flat, and the Einstein tensor Ric-1/2 Rg is bounded above, then parabolicity is preserved along the flow and the conjugate radius of g(t) is finite for every t∈(0,T]. As an application, we prove that a complete noncompact gradient shrinking Ricci soliton whose volume growth is subquadratic, in the sense that liminf_(r→∞)Vol(B(p,r))/r²=0, has finite conjugate radius.</description><category>Ricci flow</category><category>Ricci solitons</category><category>Ricci-flat &amp; Calabi–Yau</category><category>Scalar curvature</category><category>Boundaries &amp; non-compact</category></item>
<item><title>On the geometry of asymptotically conical Ricci shrinkers (II): strong uniqueness</title><link>https://neckpinch.com/papers/2610.41345/</link><guid isPermaLink="false">arxiv:2610.41345</guid><pubDate>Fri, 30 Oct 2026 00:00:00 GMT</pubDate><description>Yu Li, Longhuan Yan, Wenjia Zhang — We prove strong uniqueness of tangent flows at the first singular time of a closed Ricci flow when one tangent flow is generated by a complete smooth asymptotically conical Ricci shrinker. The modified flow converges to this shrinker in a fixed gauge, with quantitative estimates on expanding domains. The main ingredients are a Łojasiewicz-Simon inequality for Perelman&apos;s entropy, based on the global weighted divergence-free gauge constructed in the preceding paper, and estimates controlling the geometric radius under Ricci flow.</description><category>Ricci flow</category><category>Ricci solitons</category><category>Singularities</category><category>Perelman entropy</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Blowdowns along Ricci flow in dimension four</title><link>https://neckpinch.com/papers/2611.00139/</link><guid isPermaLink="false">arxiv:2611.00139</guid><pubDate>Thu, 29 Oct 2026 00:00:00 GMT</pubDate><description>Dain Kim, Tristan Ozuch — We show that the blowdown shrinking Ricci soliton of Feldman, Ilmanen and Knopf is strictly dynamically stable in the following strong local sense: (1) The Ricci flow from every metric on a closed 4-manifold containing a region close to a rescaling of a sufficiently large compact subset of the soliton in either orientation and with controlled geometry elsewhere develops a singularity with unique tangent flow modeled on the soliton. (2) The singular time slice has an isolated conical singularity, and by Gianniotis-Schulze the flow can be continued by blowing down a sphere of self-intersection ±1. (3) On a closed 4-manifold, the set of metrics whose Ricci flows have their first singularity modeled on the soliton is C¹⁴-open. It is nonempty if and only if the manifold contains a sphere of self-intersection ±1. (4) The soliton is strongly rigid among shrinking Ricci solitons. As applications, we construct C¹⁴-open sets of initial data whose Ricci flows perform any prescribed ordered sequence of blowdowns. (1) Every closed simply connected smooth 4-manifold, including spin and exotic examples, can be reached by Ricci flow from a standard kℂP}²\#ℓℂP}², through finitely many blowdown singularities. (2) On the standard 2ℂP}²\#9ℂP}², there are infinitely many open sets of initial metrics whose Ricci flows, after a single blowdown, reach pairwise nondiffeomorphic manifolds. The proof uses the spectral analysis of Naff and the second author and deals with the gauge-fixing problem along Ricci flow through a Ważewski argument inspired by Stolarski. We also use Bamler-Lai&apos;s PDE-ODI principle. Except for continuation (requiring nonnegative curvature of the asymptotic cone), all results apply to linearly stable nonflat asymptotically conical shrinkers in all dimensions.</description><category>Ricci flow</category><category>Ricci solitons</category><category>Singularities</category><category>4-manifolds</category><category>Boundaries &amp; non-compact</category><category>Eigenvalues &amp; spectrum</category></item>
<item><title>Steady conformally Kähler Ricci solitons with isoparametric potential</title><link>https://neckpinch.com/papers/2610.40994/</link><guid isPermaLink="false">arxiv:2610.40994</guid><pubDate>Thu, 29 Oct 2026 00:00:00 GMT</pubDate><description>Ernani Ribeiro, Hung Tran — We classify complete, non-compact, simply connected, irreducible four-dimensional steady gradient Ricci solitons that are globally conformally Kähler and have an isoparametric potential. The steady Ricci solitons are U(2)-invariant nuts on ℝ⁴, including the Bryant and Cao solitons, and bolts on S² × ℝ² and on 𝓞(−m)→ℂP}¹. For each m≥3 there is exactly one non-collapsed bolt. A key step, valid for Ricci solitons of every sign, is that away from the locally conformally flat case, the conformal factor is aligned with the potential function, which yields cohomogeneity-one symmetry.</description><category>Ricci solitons</category><category>Kähler–Ricci solitons</category><category>(Non)collapsing</category><category>4-manifolds</category><category>Kähler geometry</category><category>Homogeneous spaces</category><category>Boundaries &amp; non-compact</category></item>
<item><title>On the geometry of asymptotically conical Ricci shrinkers (I): weighted analysis</title><link>https://neckpinch.com/papers/2610.39814/</link><guid isPermaLink="false">arxiv:2610.39814</guid><pubDate>Thu, 29 Oct 2026 00:00:00 GMT</pubDate><description>Yu Li, Longhuan Yan, Wenjia Zhang — We develop the weighted Sobolev and Hölder analysis needed to study perturbations of complete asymptotically conical (AC) Ricci shrinkers. Weighted elliptic estimates yield a global weighted divergence-free slice in spaces that retain the asymptotic data at infinity. As a geometric application, we prove pointed Gromov-Hausdorff rigidity of nontrivial AC shrinkers with vanishing infinitesimal solitonic deformation space.</description><category>Ricci solitons</category><category>Limit spaces &amp; RCD</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Genus Increase in Closed Mean Curvature Flows</title><link>https://neckpinch.com/papers/2610.35000/</link><guid isPermaLink="false">arxiv:2610.35000</guid><pubDate>Mon, 26 Oct 2026 00:00:00 GMT</pubDate><description>Jingwen Chen — We construct closed mean curvature flows with arbitrarily large genus increase in every smooth Riemannian three-manifold, giving counterexamples to Ilmanen&apos;s genus-reduction conjecture. We prove that a compact hypersurface with a single isolated conical singularity and a power rate of convergence to its cone admits a mean curvature flow whose forward rescaled limit is a prescribed expander in the tangent space at the singular point, smoothly asymptotic to that cone. Combining this theorem with closed mean curvature flows with prescribed tangent flows (arXiv:2405.15577, arXiv:2607.23879) and the noncompact counterexample (arXiv:2605.09657) gives the desired examples.</description><category>Mean curvature flow</category><category>Ricci solitons</category><category>Singularities</category><category>3-manifolds</category><category>Boundaries &amp; non-compact</category></item>
<item><title>The global structure of bi-rotational self-expanders</title><link>https://neckpinch.com/papers/2610.25833/</link><guid isPermaLink="false">arxiv:2610.25833</guid><pubDate>Mon, 19 Oct 2026 00:00:00 GMT</pubDate><description>Gregŕio Silva Neto — We describe the self-expanders of the mean curvature flow in ℝ^(p+q+2) invariant under O(p+1)× O(q+1). Apart from the Clifford minimal cone, every such hypersurface is complete, proper and noncompact, and belongs to one of three families: two one-parameter families of embedded hypersurfaces diffeomorphic to ℝ^(p+1)×S^(q) or to ℝ^(q+1)×S^(p), whose profile curves leave an axis, and a two-parameter family diffeomorphic to ℝ×S^(p)×S^(q), parametrized by the point of the profile curve closest to the origin, which is the generic family: its set of initial conditions is open and of full measure in the phase space. Every end is asymptotically conical, with explicit decay rates, and every such hypersurface has Euclidean volume growth. A profile curve of the third family has at most one loop, and the point of the curve closest to the origin lies on that loop.</description><category>Mean curvature flow</category><category>Self-shrinkers &amp; translators</category><category>Boundaries &amp; non-compact</category><category>Minimal &amp; CMC surfaces</category></item>
<item><title>The global structure of bi-rotational self-shrinkers</title><link>https://neckpinch.com/papers/2610.25831/</link><guid isPermaLink="false">arxiv:2610.25831</guid><pubDate>Mon, 19 Oct 2026 00:00:00 GMT</pubDate><description>Gregório Silva Neto — We describe the global structure of the self-shrinkers of the mean curvature flow in ℝ^(p+q+2) invariant under O(p+1)× O(q+1), without assuming properness or embeddedness. The main tool is a pair of piecewise monotone quantities along the profile curves, in the spirit of Hsiang&apos;s analysis of constant mean curvature hypersurfaces. We prove that every such self-shrinker other than the two invariant cylinders intersects both of them transversely, and all of them except the Clifford minimal cone are complete. Apart from those of the cylinders, each end is either asymptotic to a cone or meets both cylinders infinitely many times. Consequently, a complete noncompact example is proper if and only if all its ends are asymptotically conical, and this is equivalent to polynomial volume growth, to finite entropy, and to finitely many intersections with the cylinders. The reduced flow preserves a finite measure, and for almost every initial condition the profile curve is either closed or generates a complete nonproper self-shrinker of infinite entropy. We also bound the winding of the profile curve by its number of cylinder crossings and localize its self-intersections.</description><category>Mean curvature flow</category><category>Self-shrinkers &amp; translators</category><category>Boundaries &amp; non-compact</category><category>Minimal &amp; CMC surfaces</category></item>
<item><title>The Singular Fibration of Collapsing RCD Spaces with Reifenberg Local Covers</title><link>https://neckpinch.com/papers/2610.17229/</link><guid isPermaLink="false">arxiv:2610.17229</guid><pubDate>Mon, 12 Oct 2026 00:00:00 GMT</pubDate><description>Shaosai Huang — Let compact RCD(κ,N) spaces converge in the measured Gromov–Hausdorff sense, and suppose that they have (δ,ρ)-Reifenberg local covers for one fixed ρ&gt;0, with |κ|ρ²≤1 and δ small. We prove that, along a subsequence, the spaces are singular fibrations over the limit: their canonical frame spaces converge to a topological manifold with a locally linear action of O(n) whose quotient is the limit; for large indices the frame spaces fibre over this manifold, by maps that commute with O(n), with fibres homeomorphic to nilmanifolds; and the induced maps to the limit are, near every point, quotients of products by the isotropy group, with fibres homeomorphic to infranilmanifolds. As applications, we extend a fibration theorem of Honda and Zhang to non-smooth RCD spaces whose local covers have injectivity radius bounded below, and we show that for aspherical spaces the isotropy groups are finite, the fibre groups inject into the fundamental groups, and the limit is the quotient of a contractible manifold by a proper cocompact action; under Rong&apos;s condition Aₛ it is a closed aspherical manifold. Three appendices treat smooth manifolds with Ric≥−(n-1) and small local rewinding Reifenberg error: a uniform short-time Ricci flow with |Rm|≤α/t, also for complete non-compact data, where it is unique among complete flows with curvature at most A/t; a second construction with affine nilmanifold bundles; and, conditional on Nifa&apos;s construction, examples showing that rewinding volume control alone does not give continuous Gromov–Hausdorff approximations with small error.</description><category>Ricci flow</category><category>(Non)collapsing</category><category>Weak &amp; singular flows</category><category>Limit spaces &amp; RCD</category><category>Homogeneous spaces</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Asymptotically conical shrinking ends of the r-mean curvature flow: rotational construction and uniqueness</title><link>https://neckpinch.com/papers/2610.14227/</link><guid isPermaLink="false">arxiv:2610.14227</guid><pubDate>Fri, 09 Oct 2026 00:00:00 GMT</pubDate><description>Hilário Alencar, Márcio Batista, Gregório Silva Neto — For 1≤ r≤ n-1 we study shrinking self-similar ends of the r-mean curvature flow, Sᵣ=c⟨ X,N⟩ with c&lt;0, that are asymptotic to a cone. For every rotational cone of positive slope we construct a smooth embedded rotational end and prove that its profile is the only positive solution of the profile equation with the prescribed slope at infinity. Its angular defect xu&apos;−u is strictly negative, which yields r-admissibility, and the profile has a complete asymptotic expansion for u(x)/x in powers of x^(−(r+1)), valid after arbitrary differentiation. The profiles depend real analytically on the slope and, on sufficiently distant exterior regions, foliate the image of the corresponding family. Our main result removes the symmetry assumption: two ends that converge smoothly, with multiplicity one, to the same circular cone coincide outside a compact set. The proof transforms the equation for their difference into an almost-eigenfunction inequality for a drift Laplacian on an auxiliary conical metric and applies Bernstein&apos;s asymptotic analysis on weakly conical ends. The argument extends to strictly r-admissible cones whose links have constant principal curvatures.</description><category>Mean curvature flow</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category><category>Long-time existence &amp; convergence</category><category>Eigenvalues &amp; spectrum</category></item>
<item><title>Direct proofs for spaces with cyclic parallel Ricci tensor</title><link>https://neckpinch.com/papers/2610.12930/</link><guid isPermaLink="false">arxiv:2610.12930</guid><pubDate>Fri, 09 Oct 2026 00:00:00 GMT</pubDate><description>Fengyuan Zhang — We give direct proofs of rigidity results for gradient Ricci solitons, compact quasi-Einstein manifolds with boundary, and critical spaces with cyclic parallel Ricci tensor. For solitons and quasi-Einstein manifolds, successive traces of first-order pointwise identities yield quadratic equations for the Ricci tensor and its modification. These equations imply radial flatness and radial Q-flatness, respectively, and the corresponding global rigidity theorems apply. For critical spaces, comparison of two expressions for the Laplacian of the Hessian gives a pointwise tensor identity whose scalar contraction yields a weighted divergence formula. Integration then gives the vacuum static, CPE, and Miao–Tam conclusions. The same comparison also proves Ricci parallelism pointwise for solitons and quasi-Einstein manifolds.</description><category>Ricci solitons</category><category>Einstein metrics</category><category>Almost &amp; η-Ricci solitons</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Compact Mean Curvature Flows from Non-Compact Initial Data</title><link>https://neckpinch.com/papers/2610.12817/</link><guid isPermaLink="false">arxiv:2610.12817</guid><pubDate>Thu, 08 Oct 2026 00:00:00 GMT</pubDate><description>Theodora Bourni, Nathan Burns, Marcus Flook — We construct compact, embedded solutions to the mean curvature flow in ℝⁿ⁺¹ that arise from various non-compact initial data and exist for a finite time.</description><category>Mean curvature flow</category><category>Singularities</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Radial Powered Mean Curvature Flow with Robin Boundary Conditions</title><link>https://neckpinch.com/papers/2610.08283/</link><guid isPermaLink="false">arxiv:2610.08283</guid><pubDate>Tue, 06 Oct 2026 00:00:00 GMT</pubDate><description>Tianhong Pu, Xiaoqian Xin, Lixia Yuan — We study a positive radial graph evolving by V=H^α+b, with α&gt;0 and b&lt;0, in the unit cylinder and with uᵣ(1,t)=u(1,t). We separate finite-time continuation estimates from the time-uniform interior estimates needed for convergence of normalized translates. On existing classical intervals we prove height and gradient bounds and an explicit conversion of velocity bounds into estimates for H, uᵣ/r, and uᵣᵣ. We derive the correct boundary defect for comparisons with finite-slope translators. Under independent interior velocity bounds and two-sided slope trapping, we prove compactness and identify every translated limit with the cup translator. We identify the radial zero-number comparison still required to establish that trapping. Stationary caps and power-law Robin laws are included.</description><category>Mean curvature flow</category><category>Self-shrinkers &amp; translators</category><category>Singularities</category><category>Limit spaces &amp; RCD</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Asymptotic Dynamics of Forced Curvature Flow in a Planar Strip with Robin Boundary Conditions</title><link>https://neckpinch.com/papers/2610.08270/</link><guid isPermaLink="false">arxiv:2610.08270</guid><pubDate>Tue, 06 Oct 2026 00:00:00 GMT</pubDate><description>Tianhong Pu, Xiaoqian Xin, Lixia Yuan, Xiaoyu Zhang — We study the graphical forced mean curvature flow in a planar strip subject to Robin boundary conditions. The normal velocity is prescribed by V=H+b, where b&gt;0 is constant and H denotes the curvature of the graph. We consider positive even solutions and reduce the problem to the half interval. The main results describe the degeneration produced by the Robin condition: the height, the instantaneous velocity, and the spatial gradient diverge, while the normalized slope uₓ/u converges to one away from the symmetry axis. The normalized velocity uₜ/u converges to the forcing parameter b. The curvature converges to zero in the interior in an integral sense, whereas its horizontal curvature measure concentrates at the symmetry axis.</description><category>Mean curvature flow</category><category>Other curvature flows</category><category>Volume-preserving &amp; constrained flows</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Strong Uniqueness for Instantaneously Complete Chern-Ricci Flow</title><link>https://neckpinch.com/papers/2610.08233/</link><guid isPermaLink="false">arxiv:2610.08233</guid><pubDate>Tue, 06 Oct 2026 00:00:00 GMT</pubDate><description>Shaochuang Huang, Zhuo Peng — In this paper, we study strong uniqueness for smooth instantaneously complete Chern-Ricci flows on noncompact complex manifolds. Under suitable reference metric and positivity assumptions, we establish strong uniqueness for initial Hermitian metrics which are Kähler outside a compact set. The initial metric may be incomplete, and no curvature, metric comparison, or growth bounds are imposed on the evolving solutions. In particular, we obtain strong uniqueness from complete initial metrics in this class with bounded Chern-Ricci curvature. We also prove stationarity of flows from the Euclidean metric on ℂⁿ and uniqueness of the instantaneously complete flow from the Euclidean metric on the complex unit ball for all positive time. Finally, on complex surfaces, we show that a Ricci flow remaining Hermitian for a fixed complex structure is Kähler at all times if it is Kähler at one time, and derive a corresponding strong uniqueness result for Ricci flows in this class.</description><category>Ricci flow</category><category>Generalized &amp; G₂ flows</category><category>Kähler geometry</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Area-preserving curvature flow for open curves with general contact angles on skew lines</title><link>https://neckpinch.com/papers/2610.05909/</link><guid isPermaLink="false">arxiv:2610.05909</guid><pubDate>Mon, 05 Oct 2026 00:00:00 GMT</pubDate><description>Fuya Hiroi — We study an area-preserving curvature flow for planar open curves whose end points lie on skew lines and meet the lines at general contact angles. In previous studies of moving boundary problems for higher-order geometric gradient flows, the right-angle condition has often been imposed to ensure that the evolving curves naturally satisfy the boundary conditions. However, under general contact-angle conditions, the evolution must be described by a free boundary problem. Under suitable assumptions on the contact angles θ_±, the angle θ between the skew lines, and the initial data γ₀, we prove global-in-time existence and uniqueness up to reparametrization. We further prove that, after choosing a constant-speed parametrization at each time, the solution converges exponentially to a circular arc with the same signed area as the initial curve. Our analysis is based on a formulation of the evolution as a free boundary problem together with the derivation of uniform a priori estimates.</description><category>Other curvature flows</category><category>Volume-preserving &amp; constrained flows</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category><category>Free boundary &amp; capillary</category><category>Long-time existence &amp; convergence</category></item>
<item><title>Scalar curvature bounds and tangent cones for Kähler–Ricci shrinkers</title><link>https://neckpinch.com/papers/2610.05643/</link><guid isPermaLink="false">arxiv:2610.05643</guid><pubDate>Mon, 05 Oct 2026 00:00:00 GMT</pubDate><description>Yu Li, Junsheng Zhang — We prove a uniform scalar curvature bound, depending only on the dimension, for Kähler–Ricci shrinkers. We also prove that every noncompact Kähler–Ricci shrinker has a unique tangent cone at infinity, naturally homeomorphic to the base of its polarized Fano fibration. For shrinkers with maximal volume growth, this cone is isometric to the metric completion of the regular part equipped with the intrinsic distance induced by the limiting Kähler metric.</description><category>Ricci solitons</category><category>Kähler geometry</category><category>Scalar curvature</category><category>Boundaries &amp; non-compact</category><category>Analytic minimal model program</category></item>
<item><title>A Matsushima theorem, uniqueness and K-polystability for Kähler-Ricci shrinkers</title><link>https://neckpinch.com/papers/2610.03592/</link><guid isPermaLink="false">arxiv:2610.03592</guid><pubDate>Fri, 02 Oct 2026 00:00:00 GMT</pubDate><description>Carlos Esparza, Junsheng Zhang — For noncompact smooth Kähler-Ricci shrinkers, we prove a Matsushima theorem identifying the centralizer of the soliton field with the complexification of its Killing centralizer, uniqueness up to biholomorphism on a fixed complex manifold, and K-polystability of the associated polarized Fano fibration.</description><category>Ricci solitons</category><category>Kähler geometry</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category><category>Kähler–Einstein &amp; K-stability</category><category>Analytic minimal model program</category></item>
<item><title>On the uniqueness of Ricci flows from certain Alexandrov spaces</title><link>https://neckpinch.com/papers/2610.03129/</link><guid isPermaLink="false">arxiv:2610.03129</guid><pubDate>Fri, 02 Oct 2026 00:00:00 GMT</pubDate><description>Laura Flower — We consider the problem of uniqueness of Ricci flows, starting from singular initial data. Even when the initial data is smooth and smoothly obtained, in the complete noncompact case uniqueness is not known in full generality. When starting from nonsmooth initial data, very little is known, even in the compact case. We obtain a uniqueness result for Ricci flows with scaling-invariant curvature bounds, a suitable noncollapsing assumption, and sectional curvature lower bounds, coming out of (possibly singular) Reifenberg spaces. As a consequence of our result, and existence results obtained by Simon–Topping and Lai, there is a canonical way to define a smooth structure on any Reifenberg uniformly volume-noncollapsed PIC2 limit space. Further, we obtain a diffeomorphic version of Perelman&apos;s stability theorem for these limit spaces.</description><category>Ricci flow</category><category>(Non)collapsing</category><category>Weak &amp; singular flows</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Ricci flow on manifolds with positive isotropic curvature in all dimensions</title><link>https://neckpinch.com/papers/2610.02325/</link><guid isPermaLink="false">arxiv:2610.02325</guid><pubDate>Thu, 01 Oct 2026 00:00:00 GMT</pubDate><description>Simon Brendle, Raphael Tsiamis — We extend the classification of manifolds with positive isotropic curvature to all dimensions n ≥ 5. This result also completes the classification of uniformly positive isotropic curvature on complete non-compact κ-noncollapsed ancient solutions and gradient shrinking Ricci solitons. The proof involves a construction of pinching cones in all dimensions, refining and extending to all dimensions the results of the first author. We have used MATHEMATICA to find viable parameters for the cone families. The final presentation is self-contained and can be verified manually. No stage of this work involved LLMs.</description><category>Ricci flow</category><category>Ricci solitons</category><category>Ancient solutions</category><category>(Non)collapsing</category><category>Curvature pinching</category><category>Sphere theorems</category><category>Boundaries &amp; non-compact</category></item>
<item><title>On asymptotically conical curve shortening flows with convex projections</title><link>https://neckpinch.com/papers/2609.28337/</link><guid isPermaLink="false">arxiv:2609.28337</guid><pubDate>Wed, 23 Sep 2026 00:00:00 GMT</pubDate><description>Alexander Mramor — In this work we study the long term behavior of the curve shortening flow of asymptotically conical curves with convex projections in ℝ³.</description><category>Curve shortening</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Cohomogeneity one solutions of the IIB system</title><link>https://neckpinch.com/papers/2609.28280/</link><guid isPermaLink="false">arxiv:2609.28280</guid><pubDate>Wed, 23 Sep 2026 00:00:00 GMT</pubDate><description>Lorenzo Foscolo, Mario Garcia-Fernandez — The IIB system is a system of PDEs for an SU(3)–structure and a positive function on a 6-manifold. Its solutions describe conformally balanced pluriclosed Hemitian metrics on complex 3-folds with holomorphically trivial canonical line bundle. In particular, solutions of the IIB system are steady solitons for the generalized Ricci-flow and Bismut–Hermitian–Einstein metrics. In this paper we study cohomogeneity one solutions of the IIB system. We construct 1-parameter families (up to scaling symmetries) of complete non-compact non-Kähler solutions on the smoothing of the conifold with controlled geometry at infinity. The generic member of the family is asymptotically conical with tangent cone at infinity the Calabi–Yau cone metric on the conifold. As a limit of the family we recover an explicit solutions known in the physics literature as the Chamseddine–Volkov/Maldacena–Nuñez solution, which has an exotic asymptotic geometry. We show that there are no complete cohomogeneity one solutions on crepant resolutions of the conifold (or its quotient), but we also establish the existence of an analogous 1-parameter family of forward complete solutions defined on exterior domains of the conifold with prescribed incomplete behaviour along the interior boundary and similar asymptotic behaviour at infinity. As a byproduct of these existence results, we produce infinitely many complete non-compact non-Kähler Bismut–Hermitian–Einstein metrics in complex dimension 3 with full holonomy of the Bismut connection, in contrast to the holonomy reduction forced upon compact examples. We also find infinitely many such complete non-compact full-holonomy non-Kähler examples (with at least two ends) in complex dimension 2 by revisiting a construction due to Callan–Harvey–Strominger in the physics literature.</description><category>Ricci flow</category><category>Generalized &amp; G₂ flows</category><category>Ricci solitons</category><category>Einstein metrics</category><category>Ricci-flat &amp; Calabi–Yau</category><category>3-manifolds</category><category>Kähler geometry</category><category>Homogeneous spaces</category><category>Boundaries &amp; non-compact</category></item>
<item><title>A continuous Positive Mass Theorem for perturbations of Euclidean space</title><link>https://neckpinch.com/papers/2609.25550/</link><guid isPermaLink="false">arxiv:2609.25550</guid><pubDate>Tue, 22 Sep 2026 00:00:00 GMT</pubDate><description>Paula Burkhardt-Guim — We prove a Positive Mass Theorem for C⁰-asymptotically flat Riemannian metrics with nonnegative scalar curvature in a weak sense that are sufficiently uniformly close to Euclidean space. More precisely, we show that a C⁰-asymptotically flat Riemannian metric that is a C⁰ perturbation of Euclidean space with nonnegative scalar curvature in the sense of Ricci flow has nonnegative mass, where the mass is given by a C⁰ analog of the classical ADM mass previously introduced by the author.</description><category>Ricci flow</category><category>Scalar curvature</category><category>Boundaries &amp; non-compact</category><category>Physics</category></item>
<item><title>Linear Stability of Steady and Expanding Kähler-Ricci Solitons</title><link>https://neckpinch.com/papers/2609.21472/</link><guid isPermaLink="false">arxiv:2609.21472</guid><pubDate>Fri, 18 Sep 2026 00:00:00 GMT</pubDate><description>Lucas Lavoyer, Adam Thompson — We prove linear stability of all steady and expanding gradient Kähler-Ricci solitons. In the expanding case, we prove strict linear stability under very general assumptions. In particular, every asymptotically conical expanding gradient Kähler-Ricci soliton is strictly linearly stable.</description><category>Ricci solitons</category><category>Kähler–Ricci solitons</category><category>Kähler geometry</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Global Analysis: An Introduction to Nonlinear Analysis and Its Variational Methods on Riemannian Manifolds</title><link>https://neckpinch.com/papers/2609.14580/</link><guid isPermaLink="false">arxiv:2609.14580</guid><pubDate>Sun, 13 Sep 2026 00:00:00 GMT</pubDate><description>Carlos Daniel Velázquez-Mendoza, María de los Ángeles Sandoval-Romero, Romulo Diaz Carlos — This monograph develops an introduction to global analysis centered on the interaction between differential geometry, functional analysis, partial differential equations, and variational methods on Riemannian manifolds. Beginning with smooth and Riemannian geometry, it develops Sobolev spaces, distributions, interpolation and fractional regularity, differential and pseudodifferential operators on vector bundles, elliptic theory, heat methods, bounded geometry, and trace theorems. It then treats Fredholm and index theory, culminating in the Atiyah–Singer index theorem, followed by geometric evolution equations and Ricci flow, infinite-dimensional geometry on Banach and Hilbert manifolds, and variational methods including the direct method, Palais–Smale theory, deformation arguments, the mountain pass theorem, and the Nehari method. Particular emphasis is placed on explicit proofs, the passage from local Euclidean estimates to intrinsic global statements, and the precise geometric hypotheses required in compact, noncompact, and boundary settings. The text is intended for advanced undergraduate and graduate students, as well as readers approaching global analysis from geometry or differential equations.</description><category>Ricci flow</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Kählerity of complete almost-Kähler gradient shrinking Ricci solitons</title><link>https://neckpinch.com/papers/2609.00840/</link><guid isPermaLink="false">arxiv:2609.00840</guid><pubDate>Tue, 01 Sep 2026 00:00:00 GMT</pubDate><description>Junming Xie — In this paper, we prove that any complete, compact or noncompact, almost-Kähler gradient shrinking Ricci soliton is Kähler in arbitrary even dimension. Among other applications, combining our result with the classification of complete gradient shrinking Kähler-Ricci solitons in complex dimension two, we obtain a full classification of complete almost-Kähler gradient shrinking Ricci solitons in real dimension four.</description><category>Ricci solitons</category><category>Kähler–Ricci solitons</category><category>4-manifolds</category><category>Kähler geometry</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Pinching cones for positive isotropic curvature in dimensions seven and eight</title><link>https://neckpinch.com/papers/2608.26598/</link><guid isPermaLink="false">arxiv:2608.26598</guid><pubDate>Thu, 27 Aug 2026 00:00:00 GMT</pubDate><description>Jae Ho Cho — We construct and prove the transversal invariance of two families of pinching cones for the Hamilton ODE d/dtR=Q(R) in dimensions n=7,8, thereby extending the pinching estimate established by Brendle for n≥ 12 and by Chen for 9≤ n≤ 11. In dimension n=8, two steps in Chen&apos;s construction genuinely fail. The first, an estimate for the second cone family, is repaired by retaining a coupling discarded in the dimension-general argument. The second is the gluing of the two cone families, for which Chen&apos;s estimate fails at n=8 by a definite margin. We replace it with a new argument that reduces the gluing to a single linear inequality on the cone of weakly PIC curvature operators, and prove this inequality by an explicit finite combination of frame inequalities. In dimension n=7, the two separate cone-invariance results are proved, but the gluing step is not established here. Accordingly, the resulting full pinching estimate and classification statements are restricted to dimension n=8. The n=8 pinching estimate, together with dimension-free arguments of Brendle, yields the topological classification in dimension eight of compact manifolds with positive isotropic curvature that contain no nontrivial incompressible (n-1)-dimensional space forms, extending a theorem of Brendle from n≥ 12. Together with curvature-improvement and classification results of Cho–Li and Brendle–Naff, it also yields the classification of noncompact κ-noncollapsed ancient solutions to the Ricci flow with uniformly PIC, extending a theorem of Cho–Li from n=4 or n≥ 12.</description><category>Ricci flow</category><category>Ancient solutions</category><category>(Non)collapsing</category><category>Curvature pinching</category><category>Sphere theorems</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Rigidity of compact four-dimensional weakly Einstein Ricci Solitons</title><link>https://neckpinch.com/papers/2608.25704/</link><guid isPermaLink="false">arxiv:2608.25704</guid><pubDate>Wed, 26 Aug 2026 00:00:00 GMT</pubDate><description>JeongHyeong Park, Wooseok Shin — We prove that every compact four-dimensional weakly Einstein Ricci soliton is Einstein. The nontrivial compact case reduces to the gradient shrinking setting, where a differential identity for weakly Einstein four-manifolds, together with the curvature identity for gradient Ricci solitons, yields the pointwise relation |R|²∇f=0 for the soliton potential f. Consequently, no compact proper weakly Einstein four-manifold admits a Ricci soliton structure. A noncompact homogeneous example shows that the compactness assumption is essential.</description><category>Ricci solitons</category><category>4-manifolds</category><category>Limit spaces &amp; RCD</category><category>Homogeneous spaces</category><category>Stability &amp; uniqueness</category><category>Boundaries &amp; non-compact</category></item>
<item><title>The rigity of spaces with cyclic parallel Ricci tensor</title><link>https://neckpinch.com/papers/2608.21732/</link><guid isPermaLink="false">arxiv:2608.21732</guid><pubDate>Sat, 22 Aug 2026 00:00:00 GMT</pubDate><description>Fengyuan Zhang — The aim of this paper is to classify some special Riemannian manifolds with cyclic parallel Ricci tensor, i.e. \beginequation D_ijk=\nabla_iR_jk+\nabla_jR_ki+\nabla_kR_ij=0\nonumber \endequation These structures include non-compact gradient shrinking Ricci soliton, compact (m &gt; 1)-quasi-Einstein manifolds with boundary and critical spaces. We will construct some integral identities and make use of the curvature conditions reasonably to prove that the Ricci tensor is parallel.</description><category>Ricci solitons</category><category>Einstein metrics</category><category>Almost &amp; η-Ricci solitons</category><category>Boundaries &amp; non-compact</category></item>
<item><title>Inverse Hessian Curvature Flow in Minkowski Space II: The Dirichlet problem at infinity</title><link>https://neckpinch.com/papers/2608.20037/</link><guid isPermaLink="false">arxiv:2608.20037</guid><pubDate>Thu, 20 Aug 2026 00:00:00 GMT</pubDate><description>Dake Li, Zhizhang Wang, Shiqi Yin — This paper studies self-shrinkers and the long-time behavior of the inverse σₖ curvature flow for noncompact entire spacelike strictly convex hypersurfaces in Minkowski space. In contrast to the co-compact setting, where the corresponding self-shrinker is rigid, the noncompact problem admits a rich family of self-shrinkers determined by their asymptotic data. More precisely, we formulate the self-shrinker equation as a fully nonlinear Dirichlet problem on hyperbolic space with prescribed data on its ideal boundary, and prove that every continuous negative boundary value determines a unique entire spacelike strictly convex self-shrinker. We further study the inverse σₖ curvature flow starting from an entire spacelike strictly convex hypersurface satisfying a subsolution condition at infinity and a uniform positive lower bound for its σₖ curvature. We prove global existence of the flow and show that the normalized flow converges locally smoothly to the unique self-shrinker with the same prescribed boundary value at infinity.</description><category>Other curvature flows</category><category>Self-shrinkers &amp; translators</category><category>Boundaries &amp; non-compact</category><category>Long-time existence &amp; convergence</category><category>Physics</category></item>
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