Conjectured energy-critical Type II singularity formation

From papers

Let X=({v0}{t0.9}){1u<0}\mathcal{X}=(\{v\leq 0\}\cup \{t\leq -0.9\})\cap\{-1\leq u<0\} and let C\mathcal{C} be the backward light cone. The symbols ϕ\phi, rr, ν\nu, dd, pp, and kk have the meanings in the corresponding wave-map or semilinear equation, and CsC^{s-} denotes regularity strictly below CsC^s; infinite conormal regularity is regularity to all orders with respect to the vector fields tangent to the relevant characteristic structure. Energy-critical Type II conjecture. The listed Type II solutions should exist in X\mathcal{X}: for any ν>1\nu>1, the three solutions for (d,k)=(2,1)(d,k)=(2,1) wave maps, (d,p)=(3,5)(d,p)=(3,5), and (d,p)=(4,3)(d,p)=(4,3) have respectively the stated bounds ϕC=O(rν1)\phi|_{\mathcal{C}}=\mathcal{O}(r^{\nu-1}), O(r(ν2)/2)\mathcal{O}(r^{(\nu-2)/2}), and O(rν2)\mathcal{O}(r^{\nu-2}), with the stated Cν1/2C^{\nu-1/2-} or Cν/2C^{\nu/2-} regularity and infinite conormal regularity across C\mathcal{C}; for νN2\nu\in\mathbb{N}_{\geq2} there is a smooth wave-map solution with (d,k)=(2,1)(d,k)=(2,1) and ϕC=O(rν)\phi|_{\mathcal{C}}=\mathcal{O}(r^\nu); and there are smooth solutions with the three additional decay rates O(elogr)\mathcal{O}(e^{-\sqrt{|\log r|}}), O(logr1/(2k2))\mathcal{O}(|\log r|^{-1/(2k-2)}) for d=2d=2, k2k\geq2, and O(r1elogr+O(1))\mathcal{O}(r^{-1}e^{-\sqrt{|\log r|}+O(1)}) for (d,p)=(4,3)(d,p)=(4,3). In all cases the solutions are smooth for v<0v<0, have scale-critical norm bounded away from zero as τ0\tau\to0, and the stated smoothness and conormality may be replaced by finite CkC^k versions. These conjectures organise known Type II constructions according to their exterior regularity and decay, while the cited results do not uniformly record the precise decay or high rx,rtr\partial_x,r\partial_t regularity across C\mathcal{C}; the claims therefore remain open in the supplied source context.

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Sources & referencesView supporting material

Primary source

Istvan Kadar and Lionor Kehrberger, “A note on exterior stability of isolated singularity formation for nonlinear wave equations”, arXiv:2602.03963 (2026).

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