Kahane-Khinchine type inequalities for negative exponent

We prove a concentration inequality for delta-concave measures over R-n. Us ing this result, we study the moments of order q of a norm with respect to a delta-concave measure over R-n. We obtain a lower bound for q is an eleme nt of ]-1, 0] and an upper bound for q is an element of ]0, + infinity[ in terms of the measure of the unit ball associated to the norm. This allows u s to give Kahane-Khinchine type inequalities for negative exponent.