Standard Model
The Standard Model (SM) of particle interactions is one of the major achievements of fundamental science, recently validated also with the discovery of the Higgs boson. It is the most successful theory and for many years it has been probed and systematically confirmed in collider experiments. A complete understanding of this paradigm is of fundamental importance to assess how current and future experimental results, in particular in the flavor sector, can hint at or constrain new physics scenarios. The group consists of UAB Profs. Rafel Escribano, Pere Masjuan, Joaquim Matias, Santi Peris and Antonio Pineda, postdocs Aritra Biswas, Bernat Capdevila, Alejandro Miranda and Emilio Royo as well as PhD students Cristian Alarcón, Camilo Rojas. The group activities are mainly in the Standard Model and Flavour Physics.
Radiative corrections to the tau^- → (P_1 P_2)^- nu_tau (P = pi, K) decays
Rafel Escribano
The radiative corrections to the tau^- → (P_1 P_2)^- nu_tau (P = pi, K) decays are calculated for the first time including the structure-dependent real photon corrections, which are obtained using resonance chiral theory. Our results, whose uncertainty is dominated by the model dependence of the resummation of the radiative corrections and the missing virtual structure-dependent contributions, allow for precise tests of Cabibbo-Kobayashi-Maskawa unitarity, lepton flavor universality, and nonstandard interactions.
The Holographic QCD Running Coupling Constant from the Ricci Flow
Pere Masjuan
We present a double-dilaton soft-wall model that including 1/Nc corrections can systematically connect the non-perturbative regime of alpha strong with its well-known perturbative calculation. Data on the strong effective coupling is well reproduced and the Regge trajectories of scalar, vector, and tensor meson resonances are predicted with more accuracy than previous holographic Soft-Wall models.
Optimised observables and new physics prospects in the penguin-mediated decays Bd(s)->K(*)phi
Joaquim Matias
We study the penguin-mediated Bd(s)->Kphi transitions , proposing a new optimised observable constructed from the ratio of longitudinal branching ratios of these decays, with limited hadronic uncertainties and enhanced sensitivity to New Physics. This observable exhibits a deviation at the 1.48 σ level between its experimental value and its SM determination within QCD factorisation. This result can be accommodated together with the significant deviations found for the KK* (and KK) modes in our earlier works if New Physics affects either the QCD penguin operator Q4 or the chromomagnetic dipole operator Q8g for both b → d and b → s transitions.