A Compact Counterexample to the Unrestricted $O(1)$ Interpretation of Perelman's Remark 9.6

Perelman stated in Remark~9.6 of \\emph{The entropy formula for the Ricci flow and its geometric applications} that a normalized logarithmic conjugate-heat-kernel quantity is $O(1)$ for $(q,t)$ near the pole $(p,0)$. The remark does not specify a relation between the spatial and temporal approach. Xu later restated the claim in a compact-manifold setting and showed, using the explicit heat kernel on noncompact hyperbolic space $\\mathbb{H}^3$, that the associated static formula fails in the complete category. We show that the unrestricted product-neighborhood interpretation of the $O(1)$ assertion already fails on every closed hyperbolic $3$-manifold. The proof uses the image-sum formula for the heat kernel of a compact hyperbolic quotient and a quantitative estimate showing that the nonidentity images, together with their first two spatial derivatives, are superpolynomially small relative to the identity image along an off-parabolic approach to the pole. More precisely, if d(p,qτ)=τβ,0<β<12,d(p,q_\\tau)=\\tau^\\beta, \\qquad 0<\\beta<\\frac12, then (□fˉ+fˉt)(qτ,−τ)=−12τ2β−1(1+o(1)).\\left(\\Box \\bar f+\\frac{\\bar f}{t}\\right)(q_\\tau,-\\tau) = -\\frac12 \\tau^{2\\beta-1}(1+o(1)). Hence (□fˉ+fˉt)(qτ,−τ)⟶−∞(τ↓0).\\left(\\Box \\bar f+\\frac{\\bar f}{t}\\right)(q_\\tau,-\\tau)\\longrightarrow -\\infty \\qquad (\\tau\\downarrow 0). Thus the quantity is unbounded in every ordinary product neighborhood of $(p,0)$. This does not rule out boundedness under a parabolic restriction such as d(p,q)2=O(τ),d(p,q)^2=O(\\tau), and the result has no bearing on the Poincar'e or geometrization conclusions.

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Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-09-18
DOI
https://doi.org/10.5281/zenodo.22822357
Primary Topic
Geometric Analysis and Curvature Flows
Type
preprint
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preprint

A Compact Counterexample to the Unrestricted $O(1)$ Interpretation of Perelman's Remark 9.6

Zeraoulia Rafik
Zenodo (CERN European Organization for Nuclear Research)
Geometric Analysis and Curvature Flows
preprint

A Compact Counterexample to the Unrestricted $O(1)$ Interpretation of Perelman's Remark 9.6

Zeraoulia Rafik
preprint en

Abstract

Perelman stated in Remark~9.6 of \emph{The entropy formula for the Ricci flow and its geometric applications} that a normalized logarithmic conjugate-heat-kernel quantity is $O(1)$ for $(q,t)$ near the pole $(p,0)$. The remark does not specify a relation between the spatial and temporal approach. Xu later restated the claim in a compact-manifold setting and showed, using the explicit heat kernel on noncompact hyperbolic space $\mathbb{H}^3$, that the associated static formula fails in the complete category. We show that the unrestricted product-neighborhood interpretation of the $O(1)$ assertion already fails on every closed hyperbolic $3$-manifold. The proof uses the image-sum formula for the heat kernel of a compact hyperbolic quotient and a quantitative estimate showing that the nonidentity images, together with their first two spatial derivatives, are superpolynomially small relative to the identity image along an off-parabolic approach to the pole. More precisely, if d(p,qτ)=τβ,0<β<12,d(p,q_\tau)=\tau^\beta, \qquad 0<\beta<\frac12, then (□fˉ+fˉt)(qτ,−τ)=−12τ2β−1(1+o(1)).\left(\Box \bar f+\frac{\bar f}{t}\right)(q_\tau,-\tau) = -\frac12 \tau^{2\beta-1}(1+o(1)). Hence (□fˉ+fˉt)(qτ,−τ)⟶−∞(τ↓0).\left(\Box \bar f+\frac{\bar f}{t}\right)(q_\tau,-\tau)\longrightarrow -\infty \qquad (\tau\downarrow 0). Thus the quantity is unbounded in every ordinary product neighborhood of $(p,0)$. This does not rule out boundedness under a parabolic restriction such as d(p,q)2=O(τ),d(p,q)^2=O(\tau), and the result has no bearing on the Poincar'e or geometrization conclusions.

Zenodo (CERN European Organization for Nuclear Research)
Université Djilali Bounaama Khemis Miliana (DZ)
Sustainable cities and communities
Geometric Analysis and Curvature Flows
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A Compact Counterexample to the Unrestricted $O(1)$ Interpretation of Perelman's Remark 9.6 — Zeraoulia Rafik · Zenodo (CERN European Organization for Nuclear Research) (2026) | TGRS Research Map | TGRS