1 research outputs found
Building a Scenario of Physics Beyond the Standard Model in the Flavor Sector
[eng] Recently lepton flavor universality tests in colliders have reported tensions with the Standard Model, providing an experimental hint at low energies of the effect of a new high energy theory. These tensions are known as flavor anomalies and that is why in this thesis we focus on the study of the impact of the flavor anomalies on the flavor sector of the Standard Model of particle physics. We introduce the Standard Model of particle physics and list the relevant tensions of the theory with the experiments in B decays, commenting in a brief manner the possible solutions involving new physics, as well as the main advantages and inconveniences of each new physics scenario. We first focus in a model with new heavy scalars and fermions were we only account for left-handed couplings to the Standard Model particles. We consider two possible models: one with an additional scalar and two vector-like fermions and another with two additional scalars and one vector-like fermion. The purpose of this model is to solve the tensions in FCNC decays, together with the anomalous magnetic moment of the muon, which are induced at loop-level in both models. We list the relevant constraints and show that the models are able to solve the anomalies, albeit a relatively large coupling of the muons is required. In the case of semi-leptonic decays, stringent constraints arising from B oscillations can be relaxed if the new fermions are considered Majorana particles. Then, since we cannot explain the muon magnetic moment with only left-handed couplings, we construct a model with new scalars and fermions allowing also for right- handed couplings, were we list the relevant Wilson coefficients for b quark decays to a strange quark and two muons, as well as the relevant observables acting as constraints for any number of new scalars and fermions. In order to illustrate this generic approach we supplement the Standard Model with a fourth generation of quarks and leptons. With this model we can explain FCNC anomalies and the magnetic moment of the muon avoiding all the constraints. The second kind of model that we explore is an extension of the Standard Model with scalar leptoquarks. In this case, we compute the Z- and W-decays to leptons for each one of the scalar leptoquarks at next-to-leading-logarithm approximation, and show that the finite terms can account for 20% of the total contribution for leptoquark masses of below 1.5 TeV. We also show their phenomenological relevance in a model with a singlet and a triplet, where our computation pushes the fit towards a better explanation of data. Besides, we comment on the fact that the B mixing has to be implemented carefully as it is one of the main constraints that was missing in earlier studies of these kind of models, and we also illustrate its key role in a particular model model, since it spoils the pure left- handed scenario with 2018 data. Finally, we scrutinize the FCNC process of b quark dcaying into an s quark and two leptons, in the framework of a two Higgs doublet model. We compute all the relevant Wilson coefficients performing the matching of the full theory with the low energy theory showing that it is necessary to keep the external momenta for the scalar and pseudo-scalar operators. This is the first time computation of a proper matching including all the relevant operators. We perform a phenomenological analysis of the model with the strange B meson decaying to two muons and the B meson decaying into two muons and a K meson at high momenta, where we have control of the hadronic uncertainties.[cat] Des del 2012, una serie de mesures en experiments com BaBar, Belle i LHCb, han presentat tensions respecte el model est脿ndard en deca茂ments de mesons B. Aquestes desviacions s贸n conegudes com les anomalies de sabor. En aquesta tesi interpretem les anomalies de sabor com a possibles efectes de nova f铆sica i proposem alguns models simples per poder acomodar les dades experimentals que difereixen del model est脿ndard. En primer lloc, proposem un model amb nous escalars i fermions pesats que nom茅s s鈥檃coblen als fermions tipus esquerra del model est脿ndard. En aquest escenari intentem explicar una part de les anomalies ensems amb el valor an貌mal del moment magn猫tic del mu贸. El resultat s贸n uns acoblaments relativament grans de valor 2 aproximadament. Pel que fa a resoldre part de les anomalies, tenim la possibilitat de considerar els nous fermions com fermions de Majorana, que permet reduir el valor dels acoblaments. Per tal de poder relaxar el valor dels acoblaments d鈥檜na forma m茅s general, en el seg眉ent cap铆tol proposem un model semblant per貌 amb acoblaments tipus dreta amb el model est脿ndard. En aquest model calculem totes les f贸rmules d鈥檜na manera gen猫rica i posteriorment ho particularitzem en un model de quarta generaci贸. Amb la introducci贸 d鈥檃quests acoblaments tipus dreta combinats amb els esquerra podem explicar part de les anomalies de sabor i tamb茅 el moment magn猫tic del mu贸. Seguidament, constru茂m un model amb leptoquarks escalars on estudiem alguns dels lligams m茅s importants, com els deca茂ments de Z o les oscil路lacions del mes贸 B. Posteriorment, proposem models fenomenol貌gics de 2 leptoquarks escalars on veiem l鈥檌mpacte dels lligams estudiats anteriorment. Tamb茅 discutim com els models quedarien obsolets si no fos perqu猫 les dades experimentals van canviar subtilment despr茅s de Moriond 2019. Per 煤ltim, fem un estudi de l鈥檌mpacte de dos deca茂ments: del mes贸 B estrany a dos muons i del mes贸 B al mes贸 K i dos muons dins d鈥檜n model de dos doblets de Higgs. Aqu铆 no ens centrem en les anomalies, sin贸 que mirem l鈥檌mpacte d鈥檃quests observables en el model i realitzem una comparaci贸 adequada entre la teoria efectiva i la teoria a altes enegies