On the Hardy-Littlewood majorant problem

Abstract

Consider a trigonometric polynomial f of degree N, and associate to it the polynomial F in which each coefficient of f is replaced by its absolute value. F is called the majorant of f. We show that the L^3 norm of f can be larger than that of F by a power of N. Similar examples could be constructed in which 3 is replaced by any p > 2 not equal to an even integer. This provides a negative answer to a question, the "Hardy-Littlewood majorant problem", which has been the object of some study. Had the answer been affirmative, there would have followed exciting results connected with the restriction and Kakeya conjectures.