We study the Standard Model and the new physics predictions for the leptonflavour-universality violating (LFUV) ratios in various b → s + − channels with scalar, pseudoscalar, vector, axial-vector, and Λ baryon final states, considering both unpolarized and polarized final state hadrons. In order to formulate physical observables, we use the model independent effective Hamiltonian approach and employ the helicity framework. We provide the explicit expressions of the helicity amplitudes in terms of the Wilson coefficients and the hadronic form factors by using the same kinematical configuration and polarization conventions for all decay channels. We perform the numerical analysis with new physics scenarios selected from the recent global fit analyses, having specific new physics model interpretations. We find that some of the LFUV ratios for these complementary channels in different kinematical regions have high sensitivity to new physics and the future measurements of them in Belle II and LHCb experiments, along with testing new physics/LFUV, can help to distinguish among the different new physics possibilities.

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The doubly weak transition is highly suppressed in the Standard Model, which makes it a potential channel for exploring new physics signals. We present a study of the exclusive two-body wrong sign weak decay , which belongs to this class, in the perturbative QCD framework. We perform a model independent analysis for various effective dimension-6 operators for which large effects are possible. We further analyze the considered process in the Randall-Sundrum model, including the custodially protected and the bulk-Higgs Randall-Sundrum models. Exploring the experimentally favored parameter space of these models leads to a large and significant enhancement of the decay rate compared to the Standard Model, which might be accessible in future experiments. We propose to search for the wrong sign decay via flavor-tagged time-dependent analyses, which can be performed at LHCb and Belle-II.