On extremal distributions and sharp \boldsLp-bounds\\ for sums of multilinear forms.

• Rustam Ibragimov ^[2] ; Shaturgun Sharakhmetov ^[3] ; Victor H. de la Peña ^[1]
  1. [1] Columbia University

     Columbia University

     Estados Unidos

     
  2. [2] Yale University

     Yale University

     Town of New Haven, Estados Unidos

     
  3. [3] Tashkent State Economics University

  Mostrar afiliaciones +
• Localización: Annals of probability: An official journal of the Institute of Mathematical Statistics, ISSN 0091-1798, Vol. 31, Nº. 2, 2003, págs. 630-675
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • In this paper we present a study of the problem of approximating the expectations of functions of statistics in independent and dependent random variables in terms of the expectations of functions of the component random variables. We present results providing sharp analogues of the Burkholder--Rosenthal inequalities and related estimates for the expectations of functions of sums of dependent nonnegative r.v.'s and conditionally symmetric martingale differences with bounded conditional moments as well as for sums of multilinear forms. Among others, we obtain the following sharp inequalities: E(∑nk=1Xk)t≤2max(∑nk=1EXtk,(∑nk=1ak)t) for all nonnegative r.v.'s X1,…,Xn with E(Xk∣X1,…,Xk−1)≤ak, EXtk<∞, k=1,…,n, $,$1#x003C;t#x003C;2undefined; E(∑nk=1Xk)t≤Eθt(1)max(∑nk=1bk,(∑nk=1ask)t/s) for all nonnegative r.v.'s X1,…,Xn with E(Xsk∣X1,…,Xk−1)≤ask, E(Xtk∣X1,…,Xk−1)≤bk, k=1,…,n, $,$1#x003C;t#x003C;2undefined, $,$0#x003C;s\le t-1undefined or t≥2, $,$0#x003C;s\le 1undefined, where θ(1) is a Poisson random variable with parameter 1. As applications, new decoupling inequalities for sums of multilinear forms are presented and sharp Khintchine--Marcinkiewicz--Zygmund inequalities for generalized moving averages are obtained. The results can also be used in the study of a wide class of nonlinear statistics connected to problems of long-range dependence and in an econometric setup, in particular, in stabilization policy problems and in the study of properties of moving average and autocorrelation processes. The results are based on the iteration of a series of key lemmas that capture the essential extremal properties of the moments of the statistics involved.