Percentile oscillations and the intrinsic square function

Abstract

Wilson's intrinsic square function tests the input against all the cancellative functions of a given smoothness, at every location and scale. We show that it is dominated pointwise by a sparse square function, whose coefficients are the percentile oscillations of the input modulo polynomials, at every polynomial order below the smoothness plus one. These coefficients are local sizes, which nevertheless retain essentially all the cancellation: the weighted norms of the sparse square function are equivalent to smooth grand maximal norms, for all $0<p<\infty$ and $A_\infty$ weights, with explicit dependence on the weight. These are weighted Hardy norms in the range allowed by the smoothness. Consequences include potential bounds, and weighted Hardy space estimates with the sharp factor $[w]_{A_\infty}^{1/2}$. For the derivatives of Calderón--Zygmund operators, we characterize the corresponding square function estimates by testing conditions on the polynomial symbols of their wavelet resolution. In the quadratic setting, the factor $[w]_{A_\infty}^{1/2}$ detects a transition from $\mathrm{BMO}$ testing conditions to vanishing symbols.