The Growth of Random Walks and Levy Processes

Let {Xi} be a sequence of independent, identically distributed non-degenerate random variables taking values in Rd and Sn = Iq=I Xi, Mn = MaXi-isn I Si. Define for x > 0, G(x) = P XI 1> x}, K(x) = x-2E(X, 12 XI 1 XI c x)), M(x) = I E(X, 1 { I XII c x}) 1, and h(x) = G(x) + K(x) + M(x). Then if fi = sup {a lim sup xah(x) = 01, i = sup {a lim inf xah(x) = 01, it is proved that n-'/aMn -s 0 for a (, while the lim inf is 0 and the lim sup is 00 for fi < a < S. Some alternative characterizations of the indices A, 8 are obtained as well as the analogous results for Levy processes.