Bressan's compactness conjecture for nearly incompressible flows

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Let bk:[0,+∞[×Rd→Rdb_k:[0,+\infty[\times\mathbb{R}^d\to\mathbb{R}^d, k∈Nk\in\mathbb{N}, be a sequence of smooth vector fields, and let XkX_k denote their classical flows. Assume that

∥bk∥∞+∥∇bk∥L1\|b_k\|_\infty+\|\nabla b_k\|_{L^1}

is uniformly bounded, and that the flows are uniformly nearly incompressible: for some constant C>0C>0,

1C≤det⁡(∇xXk(t,x))≤C.\frac{1}{C}\leq{\rm \det}(\nabla_xX_k(t,x))\leq C.

Bressan's compactness conjecture. Under these assumptions, the sequence {Xk}\{X_k\} is strongly precompact in Lloc⁡1([0,+∞[×Rd)L^1_{\operatorname{loc}}([0,+\infty[\times\mathbb{R}^d).

This conjecture concerns compactness of flows under uniform bounds on the vector fields and their gradients and a uniform nondegeneracy condition on the Jacobians. The source notes that a positive answer to the renormalization conjecture would imply a positive answer to this compactness conjecture.

References

Primary source

Gianluca Crippa and Laura V. Spinolo, “An Overview on Some Results Concerning the Transport Equation and its Applications to Conservation Laws”, arXiv:0911.2675 (2009).

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