Conjectured conormal regularity for Type I singularity formation

Let X=({v0}{t0.9}){1u<0}\mathcal{X}=(\{v\leq 0\}\cup \{t\leq -0.9\})\cap\{-1\leq u<0\}, and let ϕ\phi be a solution arising from smooth initial data in the stated Type I self-similar stability results, with singularity formation renormalised to t=0t=0. Write ϕ0\phi_0 for the corresponding self-similar solution, C\mathcal{C} for the backward light cone, and let {uu,xixjxjxi,rt,1}α\{u\partial_u,x_i\partial_{x_j}-x_j\partial_{x_i},r\partial_t,1\}^\alpha denote products of the listed vector fields of order α|\alpha|. Type I regularity conjecture. There exists ϵ>0\epsilon>0, depending on the equation, such that for every kNk\in\mathbb{N} and every 0αk0\leq|\alpha|\leq k, the following estimates hold on C\mathcal{C}:

{uu,xixjxjxi,rt,1}α(ϕϕ0)αrϵ\left|\{u\partial_u,x_i\partial_{x_j}-x_j\partial_{x_i},r\partial_t,1\}^\alpha(\phi-\phi_0)\right|\lesssim_{|\alpha|}r^\epsilon

for the wave-map equation with d3d\geq3, and

{uu,xixjxjxi,rt,1}α(ϕϕ0)αrϵ1\left|\{u\partial_u,x_i\partial_{x_j}-x_j\partial_{x_i},r\partial_t,1\}^\alpha(\phi-\phi_0)\right|\lesssim_{|\alpha|}r^{\epsilon-1}

for the equation with d=7d=7 and p=3p=3. These estimates assert the additional conormal and rtr\partial_t regularity needed for the exterior stability argument. The conjecture concerns precise quantitative control not supplied by the preceding stability theorem, and its resolution is not indicated here.

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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