The leading chiral electromagnetic correction to the nonleptonic Delta I=3/2 amplitude in kaon decays

In kaon decay, electromagnetic radiative corrections can generate shifts in the apparent Delta I = 3/2 amplitude of order alpha A(0)/A(2) similar to 2 2 alpha. In order to know the true Delta I = 3/2 amplitude for comparison w ith lattice calculations and phenomenology, one needs to subtract off this electromagnetic effect. We provide a careful estimate of the leading electr omagnetic shift in the chiral expansion of the amplitude, which shows that it is smaller than naive expectations, with a fractional shift of delta A(2 )((em))/A(2) = -0.016 +/- 0.01. (C) 1999 Elsevier Science B.V. All rights r eserved.