EN
We consider the maximal function $||(S^{a}f)[x]||_{L^{∞}[-1,1]}$ where $(S^{a}f)(t)^{∧}(ξ) = e^{it|ξ|^a}f̂(ξ)$ and 0 < a < 1. We prove the global estimate
$||{S^{a}f}||_{L²(ℝ,L^{∞}[-1,1])} ≤ C||f||_{H^{s}(ℝ)}$, s > a/4,
with C independent of f. This is known to be almost sharp with respect to the Sobolev regularity s.