LIGHT MASSES IN SHORT-DISTANCE PENGUIN LOOPS

Penguin diagrams for decays such as b --> (s,d)gamma involve virtual l oops of u or other light quarks. Logarithms of the virtual quark mass could, in principle, influence the phenomenological analysis of the de cay. It is thus important to study these logarithms to all orders in Q CD perturbation theory. In this paper we show that, at arbitrary order , the matrix elements of operators in the effective hamiltonian contri buting to b --> s gamma are finite for the limit of m(u) --> 0 in peng uin loops. (C) 1998 Elsevier Science B.V. All rights reserved.