The goal of this research is the precise investigations of the processes which are helpful to test the physics of the Standard Model and beyond it. We concentrate on the flavor sector of the theory which is still one of the sticking point in high energy physics. At the same time flavor physics possesses a rich phenomenology which makes it one of the hot topics in the current theoretical and experimental investigations. In this thesis we present the studies of several processes of particle

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... s taking place at the energy scale of O (GeV), namely neutrino interactions with nucleons and semileptonic B meson decays. For the neutrino scattering on nucleons with neutrino energies of about one GeV, we determine the form factors of the nucleon-resonance transition with the help of the recent electroproduction data. We extend the analysis to the second resonance region, where in addition to the resonance P 33 (1232), also D 13 (1520), P 11 (1440) and S 11 (1535) resonances contribute. Using the updated form factor fit we calculate the differential and total cross sections for the resonance production by neutrinos. A detailed analysis of angular distributions is done for the exclusive decays B → K, K * l l. The calculations are performed in the large recoil region using the QCD factorization formalism. We give the Standard Model predictions for the coefficients of angular distribution of B → Kll decays, namely F l H and A l FB . The predicted values are remarkable for their vanishing values in the Standard Model and small theoretical uncertainties. The sensitivity of these coefficients to New Physics is studied in a model-independent way. In the case of the decay B → K * (→ Kπ)ll we investigate eight CP asymmetries in the Standard Model and Beyond. Three of them are T-odd and five T-even CP asymmetries. In the Standard Model, where the CP violation comes from the CKM matrix, we predict the values of the CP asymmetries to be of O (10 −3 ). We also show that the current experimental bounds allow the T-odd asymmetries to be of O (1), whereas the values of the T-even asymmetries can be of O (0.