We construct counterexamples for the fractal Schrödinger convergence problem by combining a fractal extension of Bourgain's counterexample and the intermediate space trick of Du–Kim–Wang–Zhang. We confirm that the same regularity as Du's counterexamples for weighted $ L^2 $ restriction estimates is achieved for the convergence problem. To do so, we need to construct the set of divergence explicitly and compute its Hausdorff dimension, for which we use the Mass Transference Principle, a technique originated from Diophantine approximation.
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Figure 1. Representation of Theorem 1.1 for $ n = 15 $, where we show the improvement with respect to the former lower bound (1.3). The positive result refers to Theorem 2.3 in [13]
Figure 3. In blue, the unit cell $ \widetilde{X}_R^{a_1,a_2} $. On the right, $ \Omega_R^{a_1,a_2} = T(\widetilde{X}_R^{a_1,a_2}) $. In black on the right, the image by $ T $ of the original slabs, and in yellow, the image of the slabs dilated by $ a_1,a_2 $. To apply the Mass Transference Principle, we must prove that $ \Omega_k^{\boldsymbol{{a}}} $ covers a positive portion of the unit cell
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Representation of Theorem 1.1 for
Arrangement of the slabs of
In blue, the unit cell
Restrictions on
For fixed
For fixed
For fixed
Comparison between