LONG-DISTANCE CONTRIBUTION TO S-]D-GAMMA AND IMPLICATIONS FOR OMEGA(-)-]XI(-)GAMMA, B-S-]B-ASTERISK(D)GAMMA, AND B-]S-GAMMA

We estimate the long-distance (LD) contribution to the magnetic part o f the s-->d gamma transition using the vector meson dominance approxim ation (V=rho,omega,psi(i)). We find that this contribution may be sign ificantly larger than the short-distance (SD) contribution to s-->d ga mma and could possibly saturate the present experimental upper bound o n the Omega(-)-->Xi(-)gamma decay rate, Gamma(Omega---><(Xi>-gamma)(ma x)similar or equal to 3.7x10(-9) eV. For the decay B-s-->B(d) gamma, which is driver by s-->d gamma as well, we obtain an upper bound on th e branching ratio B(B-s-->B(d) gamma)<3x10(-8) from Gamma(Omega--->Xi -gamma)(max). Barring the possibility that the quantum chromodynamics coefficient alpha(2)(m(s)(2)) is much smaller than 1, Gamma(max Omega- -->Xi-gamma) also implies the approximate relation 2/3 Sigma(i)g(psi i )(2)(0)/m(psi i)(2)similar or equal to ho)(2)(0)/m(rho)(2)+1/6g(omega) (2)(0)/m(omega)(2). This relation agrees quantitatively with a recent independent estimate of the left-hand side by Deshpande, He, and Tramp etic, confirming that the LD contributions to b-->s gamma are small. W e find that these amount to an increase of (4+/-2)% in the magnitude o f the b-->s gamma transition amplitude, relative to the SD contributio n alone.