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    pdftitle={Local-Energy Embedding for Critical Control in 3D Navier--Stokes},
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\title{Local-Energy Embedding for Critical Control in 3D Navier--Stokes: \\ A Proof Program and Quantitative Criteria}

\author{Anonymous Authors \\
Affiliation \\
Address \\
\texttt{email}}

\begin{document}


\maketitle

\begin{abstract}
We develop a proof program that targets a quantitative bridge between scale-invariant local energy control and global critical $L^\infty_t L^3_x$ bounds for the three-dimensional incompressible Navier--Stokes equations. The program is motivated by the persistence of weak solutions and the weakness of known quantitative blowup rates at criticality. Building on the local energy framework and recent quantitative surveys, we formalize a covering-and-pressure decomposition approach that would convert a local concentration bound into a global critical estimate, yielding a conditional regularity criterion and explicit rate implications. We present a structured roadmap with formal definitions, provisional lemmas, and a theorem statement consistent with the currently available formalization, together with a validation plan that specifies acceptance criteria and evidence targets. The absence of executed experiments and completed formal derivations is recorded explicitly as a limitation, and the manuscript is framed as a rigorous, proof-first blueprint rather than a completed resolution.
\end{abstract}

\section{Introduction}
The three-dimensional incompressible Navier--Stokes equations remain a central open problem in mathematical physics and a foundational challenge in partial differential equations. Leray's construction of global weak solutions and the energy inequality established a durable framework for existence but did not resolve smoothness or uniqueness, leaving the core regularity question open for nearly a century \citep{leray1934_translation_arxiv1604,ozanski_pooley2017_leray_review_arxiv1708}. Subsequent advances sharpened conditional regularity criteria in critical spaces and produced explicit quantitative blowup-rate bounds, yet these rates are extremely weak and depend on delicate assumptions \citep{tao2019_quantitative_bounds_arxiv1908,barker_prange2022_quantitative_survey_arxiv2211}. The broader impact of these results spans turbulence modeling, numerical stability, and the design of physically faithful computational schemes.

This manuscript pursues a proof-first program that aims to embed scale-invariant local energy control into a global critical $L^3$ bound. The central idea is that a uniform bound on local energy at all scales should prevent concentration strong enough to drive the critical norm to infinity. By combining a covering argument with a precise pressure decomposition, one can seek a quantitative inequality that upgrades local control into global regularity. This direction explicitly targets the gap highlighted in the concentration and quantitative regularity literature, where local energy quantities are conceptually tied to blowup but lack a fully explicit critical-norm embedding \citep{barker_prange2022_quantitative_survey_arxiv2211,tao2019_quantitative_bounds_arxiv1908}.

Contributions:
\begin{itemize}
  \item We state a formal problem setting that isolates scale-invariant local energy quantities and critical norms, clarifying the assumptions needed for a localization-to-global embedding.
  \item We provide a proof roadmap based on covering and pressure localization, including provisional lemmas and a conditional theorem statement that specify the exact inequalities to be closed.
  \item We define quantitative evidence targets and acceptance criteria that would validate the embedding mechanism and quantify constants once experiments are executed.
  \item We document current limitations and a concrete future-work agenda, including the formal completion of derivations and execution of planned validation steps.
\end{itemize}

\section{Related Work}
Leray's original theory introduced global weak solutions and the energy inequality, which remain the baseline for the modern regularity problem \citep{leray1934_translation_arxiv1604}. The modern reconstruction of Leray's arguments clarifies weak-strong uniqueness and provides explicit blowup rate lower bounds for strong solutions \citep{ozanski_pooley2017_leray_review_arxiv1708}. Quantitative work by Tao established explicit (albeit weak) blowup-rate bounds in the critical $L^\infty_t L^3_x$ setting via quantitative Carleman estimates \citep{tao2019_quantitative_bounds_arxiv1908}. Barker and Prange survey the concentration and local energy framework, highlighting how local-in-space bounds relate to quantitative regularity \citep{barker_prange2022_quantitative_survey_arxiv2211}.

Critical and sum-space regularity criteria have been developed in the functional analytic literature, including sum-space conditions and Besov/Lorentz criteria that cover many scale-invariant regimes \citep{miller2020_sum_spaces_arxiv2007,xu_ha_li_wang2024_regular_criteria_arxiv2403}. Geometric constraints on blowup and component-reduction criteria provide further structure but stop short of quantitative critical embeddings \citep{miller2021_geometric_blowup_survey_arxiv2111}. In parallel, the averaged-model blowup result underscores that energy methods alone cannot settle global regularity and motivates the search for additional structure \citep{tao2014_averaged_ns_blowup_arxiv1402}. Nonuniqueness for weak solutions in the convex integration regime further emphasizes the need for sharper structural criteria for Leray-Hopf solutions \citep{buckmaster_vicol2018_nonuniqueness_arxiv1709}.

The gap motivating this work is the absence of a quantitative embedding from scale-invariant local energy control to global critical norms. Bridging this gap would align the concentration framework with critical regularity theory and provide explicit constants usable in blowup-rate bounds. Our approach synthesizes the local energy perspective with quantitative bounds to produce a testable, proof-driven program.

\section{Problem Setting and Notation}
We study the incompressible Navier--Stokes system on $\mathbb{R}^3$ with viscosity $\nu > 0$ and no external force, written as
\begin{equation}
\label{eq:ns}
\partial_t u + (u \cdot \nabla)u - \nu \Delta u + \nabla p = 0, \quad \nabla \cdot u = 0,
\end{equation}
where $u(x,t) \in \mathbb{R}^3$ is the velocity field, $p(x,t) \in \mathbb{R}$ is the pressure, and $t \in [0,T)$ with $T$ possibly finite. Our proof-first target corresponds to official statement (A): global existence and smoothness on $\mathbb{R}^3$ for smooth, divergence-free, rapidly decaying initial data with $f \equiv 0$. We consider suitable weak solutions that satisfy the local energy inequality and are compatible with Leray-Hopf initial data \citep{leray1934_translation_arxiv1604,ozanski_pooley2017_leray_review_arxiv1708}.

For $r>0$, define the local energy quantity
\begin{equation}
\label{eq:local_energy}
E_r(t) = \int_{B_r} |u(x,t)|^2 \,dx + \int_0^t \int_{B_r} |\nabla u|^2 \,dx\,d\tau + \frac{1}{r^2}\int_0^t \int_{B_r} |p|^{3/2} \,dx\,d\tau,
\end{equation}
where $B_r$ denotes a ball of radius $r$ and the pressure term is included in the standard scale-invariant local energy form \citep{barker_prange2022_quantitative_survey_arxiv2211}. We assume a scale-invariant bound
\begin{equation}
\label{eq:local_energy_bound}
\sup_{t<T} \sup_{0<r<r_0} r^{-1} E_r(t) \le M,
\end{equation}
with fixed constants $M>0$ and $r_0>0$. We denote the critical norm $\|u\|_{L^\infty_t L^3_x} = \sup_{t<T} \|u(\cdot,t)\|_{L^3(\mathbb{R}^3)}$ and use the scaling $u_\lambda(x,t) = \lambda u(\lambda x, \lambda^2 t)$ consistent with \eqref{eq:ns} \citep{miller2020_sum_spaces_arxiv2007,xu_ha_li_wang2024_regular_criteria_arxiv2403}.

Table~\ref{tab:notation} summarizes the main symbols used throughout the manuscript.

\begin{table}[t]
\caption{Notation and core quantities.}
\label{tab:notation}
\begin{center}
\small
\renewcommand{\arraystretch}{1.1}
\setlength{\tabcolsep}{4pt}
\begin{tabular}{ll}
\multicolumn{1}{c}{\bf Symbol} & \multicolumn{1}{c}{\bf Description} \\\hline
$u(x,t)$ & Velocity field solving \eqref{eq:ns}. \\
$p(x,t)$ & Pressure associated with incompressibility. \\
$\nu$ & Positive viscosity constant. \\
$B_r$ & Ball of radius $r$ in $\mathbb{R}^3$. \\
$E_r(t)$ & Local energy quantity in \eqref{eq:local_energy}. \\
$M$ & Scale-invariant bound in \eqref{eq:local_energy_bound}. \\
\end{tabular}
\end{center}
\end{table}

\section{Methodology: Local-Energy to Critical Embedding}
Our objective is to show that the bound in \eqref{eq:local_energy_bound} yields a global critical bound on $\|u\|_{L^\infty_t L^3_x}$, which in turn implies regularity via known critical criteria \citep{tao2019_quantitative_bounds_arxiv1908,barker_prange2022_quantitative_survey_arxiv2211}. The methodology combines (i) a covering argument to control $\|u\|_{L^3}$ by local energy at each scale and (ii) a pressure decomposition that retains scale invariance. These components are motivated by the concentration framework in the quantitative regularity literature \citep{barker_prange2022_quantitative_survey_arxiv2211}.

\subsection{Roadmap and algorithmic workflow}
Algorithm~\ref{alg:local_energy_embedding} summarizes the logical steps of the embedding argument and the validation checkpoints that accompany each step.

\begin{algorithm}[t]
\caption{Local-energy embedding proof workflow.}
\label{alg:local_energy_embedding}
\begin{algorithmic}
\STATE Input: suitable weak solution $u$, scale bound $M$, radius cutoff $r_0$.
\STATE Construct a covering of $\mathbb{R}^3$ by balls $\{B_r(x_i)\}$ with bounded overlap.
\STATE Decompose pressure $p = p_{\mathrm{loc}} + p_{\mathrm{harm}}$ on each ball.
\STATE Prove a covering inequality controlling $\|u(\cdot,t)\|_{L^3}$ via $r^{-1}E_r(t)$.
\STATE Control pressure terms using scale-invariant bounds on $p_{\mathrm{harm}}$.
\STATE Conclude a quantitative bound on $\|u\|_{L^\infty_t L^3_x}$ and propagate regularity.
\end{algorithmic}
\end{algorithm}

\subsection{Formal statements (provisional)}
The following definitions and lemmas are stated as explicit targets for the proof program. They are consistent with the available formalization and mirror the local energy framework in the literature \citep{barker_prange2022_quantitative_survey_arxiv2211}. The full derivations are pending completion and are recorded as open items in the limitations section.

\begin{definition}[Scale-invariant local energy]
A suitable weak solution $u$ satisfies the scale-invariant local energy bound if \eqref{eq:local_energy_bound} holds for some $M>0$ and $r_0>0$.
\end{definition}

\begin{lemma}[Covering inequality]
\label{lem:covering}
Assume \eqref{eq:local_energy_bound}. For each fixed $t<T$ there exists a covering of $\mathbb{R}^3$ by balls of radius $r \in (0,r_0)$ such that
\begin{equation}
\label{eq:covering}
\|u(\cdot,t)\|_{L^3(\mathbb{R}^3)}^3 \le C_1 \sup_{0<r<r_0} r^{-1} E_r(t) \cdot \|u(\cdot,t)\|_{L^2(\mathbb{R}^3)}.
\end{equation}
\end{lemma}
\noindent\textbf{Proof sketch.} Apply a Vitali-type covering to decompose $\mathbb{R}^3$ into bounded-overlap balls and estimate the $L^3$ norm by local $L^2$ and gradient control. The scale-invariant prefactor arises from $r^{-1}E_r(t)$, which is preserved under the Navier--Stokes scaling.

\begin{lemma}[Pressure localization]
\label{lem:pressure}
Let $p = p_{\mathrm{loc}} + p_{\mathrm{harm}}$ be the local-harmonic decomposition of the pressure on each ball in the covering. There exists a constant $C_2$ such that
\begin{equation}
\label{eq:pressure}
\frac{1}{r^2}\int_0^t \int_{B_r} |p_{\mathrm{harm}}|^{3/2} \,dx\,d\tau \le C_2 \sup_{0<\rho<r_0} \rho^{-1} E_\rho(t).
\end{equation}
\end{lemma}
\noindent\textbf{Proof sketch.} Use harmonicity of $p_{\mathrm{harm}}$ on each ball along with mean-value bounds, and control $p_{\mathrm{loc}}$ via the local energy inequality. The decomposition preserves the scale invariance of \eqref{eq:local_energy_bound}.

\begin{theorem}[Localization implies critical control]
\label{thm:local_energy_to_L3}
If a suitable weak solution satisfies \eqref{eq:local_energy_bound}, then
\begin{equation}
\label{eq:L3_bound}
\|u\|_{L^\infty_t L^3_x} \le C_3(M),
\end{equation}
and the solution remains smooth on $[0,T)$ with quantitative derivative bounds depending on $M$ and $\nu$.
\end{theorem}
\noindent\textbf{Proof sketch.} Combine \eqref{eq:covering} and \eqref{eq:pressure} to obtain \eqref{eq:L3_bound}, then invoke quantitative critical regularity theory to propagate smoothness \citep{tao2019_quantitative_bounds_arxiv1908}.

\subsection{Motivation for component choices}
The covering inequality \eqref{eq:covering} is motivated by concentration arguments in which control of local $L^2$ and gradient energy prevents $L^3$ blowup \citep{barker_prange2022_quantitative_survey_arxiv2211}. The pressure decomposition in \eqref{eq:pressure} is critical for maintaining scale invariance and aligns with the local energy definitions used in concentration-based criteria. Finally, \eqref{eq:L3_bound} connects to explicit quantitative regularity bounds, which provide a pathway to turning local control into global smoothness with explicit rate statements \citep{tao2019_quantitative_bounds_arxiv1908}.

\section{Validation Plan and Expected Evidence}
Because the formal derivations are incomplete and no computational experiments have been executed, we report a validation plan rather than results. The plan specifies which inequalities must be verified, the evidence artifacts required, and the rationale for why these artifacts test the hypotheses. Table~\ref{tab:validation} lists the acceptance criteria that will serve as evidence for Lemmas~\ref{lem:covering} and \ref{lem:pressure} and Theorem~\ref{thm:local_energy_to_L3}.

\begin{table}[t]
\caption{Planned validation criteria for the local-energy embedding. Each criterion tests a specific step in the proof roadmap and will be used as evidence once experiments and symbolic checks are executed.}
\label{tab:validation}
\begin{center}
\small
\renewcommand{\arraystretch}{1.1}
\setlength{\tabcolsep}{4pt}
\begin{tabular}{p{3.0cm}p{3.0cm}p{6.0cm}}
\multicolumn{1}{c}{\bf Target} & \multicolumn{1}{c}{\bf Quantity} & \multicolumn{1}{c}{\bf Evidence rationale} \\\hline
Covering inequality & $\Omega_r(t)=r^{-1}E_r(t)$ & Confirms the scale-invariant bound used in \eqref{eq:covering} across coverings and radii. \\
Pressure localization & $\|p_{\mathrm{harm}}\|_{L^{3/2}}$ & Tests the scale-invariant pressure bound in \eqref{eq:pressure} under different decompositions. \\
Critical control & $\|u\|_{L^\infty_t L^3_x}$ & Verifies whether the bound \eqref{eq:L3_bound} closes with explicit constants. \\
Ablation & weakened $r^{-1}$ scaling & Demonstrates failure of \eqref{eq:covering} and \eqref{eq:L3_bound} under non-scale-invariant bounds. \\
\end{tabular}
\end{center}
\end{table}

These criteria are designed to directly test the chain of implications from local energy control to global critical bounds. Evidence for the covering inequality is obtained by evaluating $\Omega_r(t)$ and verifying the scaling in \eqref{eq:covering}; pressure localization evidence focuses on whether the harmonic component remains scale invariant as required by \eqref{eq:pressure}. The critical-control criterion tests the main claim in Theorem~\ref{thm:local_energy_to_L3} and connects to the quantitative regularity theory of \citet{tao2019_quantitative_bounds_arxiv1908}. The ablation criterion isolates whether any loss of scale invariance is fatal to the argument, thereby validating the necessity of the exact scaling in \eqref{eq:local_energy_bound}.

\section{Limitations and Future Work}
The present manuscript is constrained by two gaps. First, the formal derivations of Lemmas~\ref{lem:covering} and \ref{lem:pressure} and Theorem~\ref{thm:local_energy_to_L3} are not yet fully proved; the statements are provisional and serve as precise proof targets. Second, the validation experiments and symbolic checks have not been executed due to missing dependencies, leaving the evidence columns in Table~\ref{tab:validation} unfilled. This absence of quantitative evidence limits our ability to assess constants in \eqref{eq:L3_bound} or compare the strength of the bound with existing results.

Future work will proceed along two synchronized tracks. On the analytic side, we will complete the derivations by formalizing the covering argument and the pressure decomposition in a scale-invariant setting, then reconcile the resulting constants with the quantitative regularity theory in \citet{tao2019_quantitative_bounds_arxiv1908}. On the validation side, we will run the planned benchmark suite to evaluate the acceptance criteria in Table~\ref{tab:validation}, including ablations of the scaling assumption and pressure split. These experiments will produce the evidence needed to quantify constants and validate the proof roadmap.

\section{Conclusion}
We presented a proof-first program that targets a quantitative embedding from scale-invariant local energy control to global critical $L^3$ bounds for 3D Navier--Stokes. The approach is grounded in the local energy framework and motivated by the need for explicit quantitative regularity criteria. While the formal derivations and empirical validation are incomplete, the manuscript provides a concrete roadmap with explicit inequalities, evidence targets, and a plan to connect local energy concentration to critical regularity. Completing the formal proof and executing the validation steps are the next milestones toward a rigorous, quantitative criterion that bridges local and global perspectives in the Navier--Stokes problem.




\bibliographystyle{conference}
\bibliography{references}

\appendix
\section{Reproducibility and Implementation Details}
The validation plan uses synthetic benchmark suites designed to test the scale-invariant inequalities in \eqref{eq:covering}--\eqref{eq:L3_bound}. The intended protocol includes four random seeds per configuration (9, 21, 33, 45), parameter sweeps over radii and pressure decompositions, and multiple covering schemes. Reported statistics will include mean, standard deviation, and 95\% confidence intervals for the quantities in Table~\ref{tab:validation}. The compute budget is theoretical in the sense that computations guide intuition and do not constitute proofs.

Planned sweeps include the scale cutoff $r_0 \in \{10^{-1}, 10^{-2}, 10^{-3}\}$, covering schemes in $\{\text{Vitali}, \text{dyadic grid}, \text{ball packing}\}$, pressure splits in $\{\text{local+harmonic}, \text{local+nonlocal}, \text{mollified}\}$, and scale bounds $M \in \{1,5,10\}$. Each configuration records $\Omega_r(t)$, $\|p_{\mathrm{harm}}\|_{L^{3/2}}$, and $\|u\|_{L^\infty_t L^3_x}$, as well as ablation runs that weaken the scale-invariant exponent to assess failure modes. The benchmarks approximate suitable weak-solution behavior by enforcing synthetic local energy concentration profiles rather than solving the full PDE. Once dependencies are available, the full experiment matrix will be executed and quantitative tables will be added to the main text or appendix.

\end{document}
