  The doubly weak $b\to dd{\bar s}$ and $b\to ss{\bar d}$ processes are highly
suppressed in the standard model that offer the unique opportunity to explore
new physics signals. The wrong sign decay $\smash{\overline B}^0\to K^+\pi^-$
mediated by the $b\to dd{\bar s}$ transition can be distinguished from the
penguin decay $\smash{B}^0\to K^+\pi^-$, through time dependent measurement in
experiments. We consider a model independent analysis of $\smash{\overline
B}^0\to K^+\pi^-$ decay, within the perturbative QCD approach and explore
various effective dimension-6 operators, in which large effects are possible.
We also study the doubly weak exclusive process in two example models namely
Randall-Sundrum model with custodial protection and the bulk-Higgs
Randall-Sundrum model. A large and significant enhancement of the branching
ratio, in comparison to the standard model, is observed after satisfying all
the relevant constraints on the parameter spaces of these models, which
requires to be searched in future experiments.
