FINAL-STATE INTERACTIONS AND NEW PHYSICS IN B-]PI-K DECAYS

Within the standard model, and if one assumes that soft rescattering e ffects are negligible, the CP asymmetry A(CP)(dir)(B+/--->pi(+/-)K) is predicted to be very small and the ratio R=B(B-d-->pi(-/+)K(+/-))/B(B +/--->pi(+/-K)) provides a bound on the angle gamma of the unitarity t riangle, sin(2) gamma less than or equal to R. We estimate the correct ions from soft rescattering effects using an approach based on Regge p henomenology, and find effects of order 10% with large uncertainties. In particular, we conclude that A(CP)(dir)similar to 0.2 and sin(2) ga mma similar to 1.2R could not be taken unambiguously to signal new phy sics. Using SU(3) relations, we suggest experimental tests that could constrain the size of the soft rescattering effects thus reducing the related uncertainty. Finally, we study the effect of various models of new physics on A(CP)(dir) and on R. [S0556-2821(98)01509-4].