Limit theorems for nondegenerate U-statistics of continuous   semimartingales
  This paper presents the asymptotic theory for nondegenerate $U$-statistics of high frequency observations of continuous It\^{o} semimartingales. We prove uniform convergence in probability and show a functional stable central limit theorem for the standardized version of the $U$-statistic. The limiting process in the central limit theorem turns out to be conditionally Gaussian with mean zero. Finally, we indicate potential statistical applications of our probabilistic results. 
Mark Podolskij, Christian Schmidt, Johanna F. Ziegel
math.PR math.ST stat.TH