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Résumé |
Heavy-light mesons play an important role in the search of new physics beyond the Standard Model. In particular, B-mesons properties can be used to put constraints on the matrix elements of the Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix governing flavour-changing weak decays.
The dynamics of quarks and gluons are described by Quantum Chromodynamic (QCD). This theory predicts that, at low energies, the associated coupling constant increases, making the use of perturbative methods ineffective. Lattice QCD is a non-perturbative regularization scheme of QCD, suitable for numerical simulations. However, studying heavy-light mesons remains a challenging task due to the many different energy scales that must be considered simultaneously on the lattice. In this work, I use the Heavy Quark Effective Theory (HQET), which consists in a systematic expansion of the QCD Lagrangian and correlation functions in 1/m where m is the mass of the heavy quark, combined with chiral perturbation theory for the light quark. One obtains the Heavy Meson Chiral Perturbation Theory (HMchiPT) which can be used to extrapolate lattice data, like the B and D meson decay constants that are important hadronic inputs, to the chiral limit.
After introducing the Heavy Meson Chiral Lagrangians and its different couplings, I will present the lattice computation of two such couplings. The first one is associated to the hadronic transition B*' -> B pi where B*' is the radial excitation of the vector B meson. The Generalized Eigenvalue Problem (GEVP) will be used to extract information about the excited state from the ratio of three-point to two-point correlation functions and I will discuss the phenomenological implications of our results. Then, I will present the computation of the coupling h between the scalar and the pseudoscalar B mesons using two-point correlation functions. This coupling enters the formulae used to guide the chiral extrapolations when positive parity states are taken into account. We will see that h is large compared to the other couplings and that B meson orbital excitation degrees of freedom cannot be missed in chiral loops. |
