Generic Strichartz conjecture for the Schrödinger equation on irrational tori

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Let d≥2d\geq 2 and let (β1,…,βd)∈[1,2]d(\beta_1,\dots,\beta_d)\in[1,2]^d be generic, meaning outside a Lebesgue-null set. Define

Δβ=12π(β1∂12+⋯+βd∂d2)\Delta_\beta=\frac{1}{2\pi}\left(\beta_1\partial_1^2+\cdots+\beta_d\partial_d^2\right)

on the square torus Td=[0,1]d\mathbb{T}^d=[0,1]^d. For N≥1N\geq 1, T≥1T\geq 1, and ff with Fourier support in the Euclidean ball B(0,N)B(0,N), let

θ(p)={0,p∈[1,2(d+2)d),d2(p−2(d+2)d),p∈[2(d+2)d,6),2d−2,p∈[6,∞).\theta(p)=\begin{cases}0,&p\in\left[1,\frac{2(d+2)}{d}\right),\\[2pt]\frac d2\left(p-\frac{2(d+2)}d\right),&p\in\left[\frac{2(d+2)}d,6\right),\\[2pt]2d-2,&p\in[6,\infty). \end{cases}

Generic Strichartz conjecture. For arbitrarily small ε>0\varepsilon>0, one has

∥eitΔβf∥Lp([0,T]×Td)≲εNε(1+Nd2−d+2p)[1+(TNθ(p))1/p]∥f∥L2.\left\|e^{it\Delta_\beta}f\right\|_{L^p([0,T]\times\mathbb{T}^d)}\lesssim_{\varepsilon}N^{\varepsilon}\left(1+N^{\frac d2-\frac{d+2}{p}}\right)\left[1+\left(\frac{T}{N^{\theta(p)}}\right)^{1/p}\right]\|f\|_{L^2}.

Moreover, these estimates are sharp up to factors NεN^{\varepsilon} for arbitrarily small ε\varepsilon. This conjecture predicts the optimal generic-in-parameter long-time Strichartz bounds for Schrödinger evolution on irrational rectangular tori; the use of genericity is justified by metric Diophantine approximation, while the sharpness assertion and the full range of estimates remain open in the stated generality.

References

Primary source

Yu Deng, Pierre Germain and Larry Guth, “Strichartz estimates for the Schrodinger equation on irrational tori”, arXiv:1702.05618 (2017).

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