Meson Decay with Isospin Breaking At Two Loops.

Summary, in English

In all calculations done in this thesis, the evaluation of higher order quantum corrections has been central. In the first paper included in this thesis we have investigated the effects of finite volume meson propagators for quark-antiquark vacuum expectation value at two-loop level. In the second paper we have improved the earlier calculations for the eta decay to three pions by implementing two-loop quantum corrections. The low energy constants of order p6 are estimated by means of a resonance chiral Lagrangian. In addition, the experimental charged decay rate leads to the determination for the isospin breaking quantities. Finally, we have studied the isospin breaking effects on the vector and scalar form-factor of semi-leptonic decays. Semi-leptonic kaon decays, both rare and weak semi-leptonic decays. Semi-leptonic kaon decays provide a rich laboratory to find the CKM matrix element Vus and the possible new physics beyond the Standard Model in flavor sector.