Conjectured conormal regularity for Type I singularity formation

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Let X=({v≤0}∪{t≤−0.9})∩{−1≤u<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 {u∂u,xi∂xj−xj∂xi,r∂t,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 k∈Nk\in\mathbb{N} and every 0≤∣α∣≤k0\leq|\alpha|\leq k, the following estimates hold on C\mathcal{C}:

∣{u∂u,xi∂xj−xj∂xi,r∂t,1}α(ϕ−ϕ0)∣≲∣α∣rϵ\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 d≥3d\geq3, and

∣{u∂u,xi∂xj−xj∂xi,r∂t,1}α(ϕ−ϕ0)∣≲∣α∣rϵ−1\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 r∂tr\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.

References

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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