Flavour Physics and CP Violation

These notes represent a summary of three lectures on flavour and CP violation, given at the CERNs European School of High Energy Physics in 2014. They cover flavour physics within the standard model, phenomenology of CP violation in meson mixing and decays, as well as constraints of flavour observableson physics beyond the standard model. In preparing the lectures (and consequently this summary) I drew heavily from several existing excellent and exhaustive sets of lecture notes and reviews on flavour physics and CP violation [1]. The reader is encouraged to consult those as well as the original literature for a more detailed study.Comment: 16 pages, contribution to the CERN in the Proceedings of the 2014 European School of High-Energy Physics, Garderen, the Netherlands, 18 June - 1 July 201

Flavor Changing Neutral Coupling Mediated Radiative Top Quark Decays at Next-to-Leading Order in QCD

We compute the branching ratios for the rare top quark decays t to c gamma and t to c Z mediated by effective flavor changing neutral couplings at the next-to-leading order in QCD including the effects due to operator mixing. After re-suming contributions of order [alpha_s log (Lambda / m_t)]^n, where Lambda is the scale at which the effective operators are generated, at leading log level using renormalization group methods, we compute finite matrix element corrections and study the effects of experimental kinematic cuts on the extracted branching ratios. We find that the t to c gamma decay can be used to probe also the effective operators mediating t to c g processes, since these can naturaly contribute 10% or more to the radiative decay. Conversely, any experimental signal of t to c g would indicate a natural lower bound on t to cZ, gamma.Comment: 4 pages, 3 figure

QCD Corrections to Flavor Changing Neutral Coupling Mediated Rare Top Quark Decays

Recently we have presented an analysis of flavor changing neutral coupling mediated radiative top quark decays at next-to-leading order in QCD. In the present paper we provide the details of the calculation of QCD corrections to t-> q gamma and t-> q Z decays within the effective theory approach including operator mixing. In particular, we calculate virtual matrix element corrections and the corresponding bremsstrahlung contributions. In the case of t-> q gamma we study the effects of kinematic cuts on the extracted branching ratios. Analytical formulae are given at all stages of the calculation. We find that the t-> q gamma decay can be used to probe also the effective operators mediating t-> q g processes, since these can naturally contribute 10% or more to the radiative decay, given typical experimental cuts on the decay kinematics at hadron colliders. Conversely, we argue that any positive experimental signal of the t-> q g process would indicate a natural lower bound on t-> q gamma decay rate.Comment: 12 page

Light Colored Scalar as Messenger of Up-Quark Flavor Dynamics in Grand Unified Theories

The measured forward-backward asymmetry in the t tbar production at the Tevatron might be explained by the additional exchange of a colored weak singlet scalar. Such state appears in some of the grand unified theories and its interactions with the up-quarks are purely antisymmetric in flavor space. We systematically investigate the resulting impact on charm and top quark physics. The constraints on the relevant Yukawa couplings come from the experimentally measured observables related to D0--D0bar oscillations, as well as di-jet and single top production measurements at the Tevatron. After fully constraining the relevant Yukawa couplings, we predict possible signatures of this model in rare top quark decays. In a class of grand unified models we demonstrate how the obtained information enables to constrain the Yukawa couplings of the up-quarks at very high energy scale.Comment: 13 pages, 11 figures, version as published in PR

Learning the latent structure of collider events

We describe a technique to learn the underlying structure of collider events directly from the data, without having a particular theoretical model in mind. It allows to infer aspects of the theoretical model that may have given rise to this structure, and can be used to cluster or classify the events for analysis purposes. The unsupervised machine-learning technique is based on the probabilistic (Bayesian) generative model of Latent Dirichlet Allocation. We pair the model with an approximate inference algorithm called Variational Inference, which we then use to extract the latent probability distributions describing the learned underlying structure of collider events. We provide a detailed systematic study of the technique using two example scenarios to learn the latent structure of di-jet event samples made up of QCD background events and either tt¯.Fil: Dillon, B. M.. Institute Jo?ef Stefan; EsloveniaFil: Faroughy, D. A.. Universitat Zurich; SuizaFil: Kamenik, J. F.. Institute Jo?ef Stefan; Eslovenia. University of Ljubljana; EsloveniaFil: Szewc, Manuel. Universidad Nacional de San Martín; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Minimal lepton flavor violating realizations of minimal seesaw models

We study the implications of the global U(1)R symmetry present in minimal lepton flavor violating implementations of the seesaw mechanism for neutrino masses. In the context of minimal type I seesaw scenarios with a slightly broken U(1)R, we show that, depending on the R-charge assignments, two classes of generic models can be identified. Models where the right-handed neutrino masses and the lepton number breaking scale are decoupled, and models where the parameters that slightly break the U(1)R induce a suppression in the light neutrino mass matrix. We show that within the first class of models, contributions of right-handed neutrinos to charged lepton flavor violating processes are severely suppressed. Within the second class of models we study the charged lepton flavor violating phenomenology in detail, focusing on mu to e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable contributions to these processes are naturally obtained for right-handed neutrino masses at the TeV scale. We then discuss the interplay with the effects of the right-handed neutrino interactions on primordial B - L asymmetries, finding that sizable right-handed neutrino contributions to charged lepton flavor violating processes are incompatible with the requirement of generating (or even preserving preexisting) B - L asymmetries consistent with the observed baryon asymmetry of the Universe.Comment: 21 pages, 4 figures; version 2: Discussion on possible generic models extended, typos corrected, references added. Version matches publication in JHE

The Machine Learning Landscape of Top Taggers

Based on the established task of identifying boosted, hadronically decaying top quarks, we compare a wide range of modern machine learning approaches. Unlike most established methods they rely on low-level input, for instance calorimeter output. While their network architectures are vastly different, their performance is comparatively similar. In general, we find that these new approaches are extremely powerful and great fun.Comment: Yet another tagger included

Implications of Flavor Dynamics for Fermion Triplet Leptogenesis

We analyze the importance of flavor effects in models in which leptogenesis proceeds via the decay of Majorana electroweak triplets. We find that depending on the relative strengths of gauge and Yukawa reactions the $B-L$ asymmetry can be sizably enhanced, exceeding in some cases an order of magnitude level. We also discuss the impact that such effects can have for TeV-scale triplets showing that as long as the $B-L$ asymmetry is produced by the dynamics of the lightest such triplet they are negligible, but open the possibility for scenarios in which the asymmetry is generated above the TeV scale by heavier states, possibly surviving the TeV triplet related washouts. We investigate these cases and show how they can be disentangled at the LHC by using Majorana triplet collider observables and, in the case of minimal type III see-saw models even through lepton flavor violation observables.Comment: 22 pages, 9 figures, extended discussion on collider phenomenology, references added. Version matches publication in JHE