We consider the maximal function where and 0 < a < 1. We prove the global estimate , s > a/4, with C independent of f. This is known to be almost sharp with respect to the Sobolev regularity s.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-cm91-2-1, author = {Bjorn Gabriel Walther}, title = {Estimates with global range for oscillatory integrals with concave phase}, journal = {Colloquium Mathematicae}, volume = {91}, year = {2002}, pages = {157-165}, zbl = {1005.42008}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-cm91-2-1} }
Bjorn Gabriel Walther. Estimates with global range for oscillatory integrals with concave phase. Colloquium Mathematicae, Tome 91 (2002) pp. 157-165. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-cm91-2-1/