Problem 15
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Logarithmic \(L^6\) Strichartz estimate for the circle Schrödinger propagator
Let \(e^{it\partial_x^2}\) be the free Schrödinger propagator on the circle \(\mathbb{T}=\mathbb{R}/(2\pi\mathbb{Z})\). Is it true that there exists a constant \(C>0\) such that, for all sufficiently large \(N\) and all \(f\in C^\infty(\mathbb{T})\) satisfying \(\operatorname{supp}\widehat{f}\subset[-N,N]\), the estimate
\[ \|e^{it\partial_x^2}f\|_{L^6_{t,x}([0,2\pi]\times\mathbb{T})} \le C(\log N)^{1/6}\|f\|_{L^2(\mathbb{T})} \]
holds?
Source: Anonymous.
LaTeX source
Let \(e^{it\partial_x^2}\) be the free Schr\"odinger propagator on the circle \(\mathbb T=\mathbb R/(2\pi\mathbb Z)\). Is it true that there exists a constant \(C>0\) such that, for all sufficiently large \(N\) and all \(f\in C^\infty(\mathbb T)\) satisfying \(\operatorname{supp}\widehat f\subset[-N,N]\), the estimate
\[
\|e^{it\partial_x^2}f\|_{L^6_{t,x}([0,2\pi]\times\mathbb T)}
\le
C(\log N)^{1/6}\|f\|_{L^2(\mathbb T)}
\]
holds?
Added June 23, 2026.