ScalingStacks

Robustness of potential clustering [04EC]

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Robustness of potential clustering

We revisit the potential clustering property (cf. section 3.8.3) from the geometric measure theory perspective. Assume as always that the Lagrangian integral current LL is quantitatively almost calibrated, homologous to L0L_{0}, and equipped with Lagrangian potential fLf_{L}. Given constants N∈ℕ,A∈ℝ+N\in\mathbb{N},A\in\mathbb{R}_{+}, we say LL satisfies (N,A)(N,A)-potential clustering, if

L=∑1NLi,fL​L=∑1NfLi​Li,L=\sum_{1}^{N}L_{i},\quad f_{L}L=\sum_{1}^{N}f_{L_{i}}L_{i},

for quantitatively almost calibrated, closed Lagrangian integral currents LiL_{i} with potential fLif_{L_{i}}, contained inside the support of LL, such that the oscillation of the Lagrangian potentials have uniform bounds

supLifLi−infLifLi≤A,\sup_{L_{i}}f_{L_{i}}-\inf_{L_{i}}f_{L_{i}}\leq A,

while for any i>ji>j,

supLjfLj≤infLifLi.\sup_{L_{j}}f_{L_{j}}\leq\inf_{L_{i}}f_{L_{i}}.

Without loss of generality, we assume supL0fL0−infL0fL0≤A\sup_{L_{0}}f_{L_{0}}-\inf_{L_{0}}f_{L_{0}}\leq A for the fixed Lagrangian L0L_{0}.

Remark 5.8.

Here we allow LiL_{i} to have overlapping supports. For instance, it is possible for L1=L2L_{1}=L_{2} as currents, but fL2f_{L_{2}} and fL1f_{L_{1}} differ by a constant.

We will later be interested in uniform upper bounds on N,AN,A. For now, we observe the robustness under limits:

Corollary 5.9.

Fix the choice of N,AN,A. Suppose we are given a sequence of Lagrangians L(j)L^{(j)} with potential satisfying (N,A)(N,A)-potential clustering, and assume Li(j)→LiL_{i}^{(j)}\to L_{i} as currents for 1≤i≤N1\leq i\leq N, all fLi(j)f_{L_{i}}^{(j)} have uniform L∞L^{\infty} bounds, and fLi(j)​L(j)→fLi​Lif_{L_{i}^{(j)}}L^{(j)}\to f_{L_{i}}L_{i} as currents. Then the limit L=∑1NLiL=\sum_{1}^{N}L_{i} with its potential fLf_{L} also satisfies (N,A)(N,A)-potential clustering.

Proof.

Notice a potential bound such as fL≥cf_{L}\geq c can be characterized by the positivity of the measure g↦∫L(fL−c)​g​Re​Ωg\mapsto\int_{L}(f_{L}-c)g\text{Re}\Omega. This characterization is robust under current convergence, so

supLifLi≤lim supjsupLi(j)fLi(j),infLifLi≥lim infjinfLi(j)fLi(j),\sup_{L_{i}}f_{L_{i}}\leq\limsup_{j}\sup_{L_{i}^{(j)}}f_{L_{i}^{(j)}},\quad\inf_{L_{i}}f_{L_{i}}\geq\liminf_{j}\inf_{L_{i}^{(j)}}f_{L_{i}^{(j)}},

hence the potential clustering bounds pass to the limit. ∎

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