Analysis of 'new physics' in the flavor sector using effective field theory methods

The enormous amount of data collected by the B factories as well as the perspective concerning the upcoming experiments at the LHC provide us with the opportunity to perform high precision tests of the standard model. This dissertation presents two model independent precision tests of the weak sector of the standard model using extensions of the weak currents which are set up using effective field theory methods in order to control the size of the different contributions. Constraints on the coefficients of the terms can then be obtained by comparison with experimental results. The first analysis incorporates a test of the lefthandedness of the weak interaction in the quark sector. By introducing additional weak couplings the differential and total decay rates of the inclusive semileptonic decay anti B → Xcl anti νl are calculated. The calculation includes the computation of the heavy-quark expansion which describes the interaction of the decaying b quark with respect to the background field of the B meson, up to order 1/mb4. This has been done in a new, systematic way which does not involve the calculation of gluon matrix elements. Furthermore, radiative corrections have been included up to order O(αs) including renormalization group running. The second part deals with the introduction of lepton flavor violating operators in the context of leptonic τ decays. These operators give rise to the effective four-fermion vertex τ→ll'l'' as well as the subsequent radiative decay τ→lγ*→ll'+l'-. The resulting Dalitz distributions turn out to predict completely different signatures for the radiative and the effective four-fermion vertices and provide the opportunity to check, whether the decay is induced either by a radiative or by an effective four-fermion vertex. Since different models which contain lepton flavor violation are normally more sensitive to one of those decay modes than to the other, the analysis therefore allows the comparison of the different models within an experimental analysis (orig.)