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Enquanto todos os modelos com neutrinos massivos de Majorana levam ao mesmo operador efetivo de dimensão d = 5, que não conserva número leptônico, os operadores de dimensão d = 6, obtidos a baixas energias, conservam número leptônico e são diferentes dependendo do modelo de alta energia da nova física. Derivamos os operadores de dimensão d = 6 que são característicos de modelos Seesaw genéricos, no qual a massa do neutrino resulta do intercâmbio de campos pesados que podem ser tanto singletos fermiônicos, tripletos fermiônicos ou tripletos escalares. Os operadores resultantes podem conduzir a efeitos observáveis no futuro próximo, se os coeficientes dos operadores de dimensão d = 5 e d = 6 são desacoplados. Neste trabalho apresentamos o modelo violação mínima de sabor no contexto do modelo seesaw tipo III, no qual é possível obter tal desacoplamento. Isto permite reconstruir a estrutura de sabor a partir dos valores das massas dos neutrino leves e dos parâmetros de mistura, mesmo na presença de fases de violação CP. / While all models of Majorana neutrino masses lead to the same dimension five effective operator, which does not conserve lepton number, the dimension six operators induced at low energies conserve lepton number and differ depending on the high energy model of new physics. We derive the low-energy dimension six operators which are characteristic of generic Seesaw models, in which neutrino masses result from the exchange of heavy fields which may be either fermionic singlets, fermionic triplets or scalar triplets. The resulting operators may lead to effects observable in the near future, if the coefficients of the dimension five and six operators are decoupled. In this work we present the model of minimal avor violation in the context of the type III seesaw model, in which it is possible to obtain the decoupling mentioned before. This allows to reconstruct the avour structure of the model from the values of the light neutrino masses and mixing parameters, even in the presence of CP-violating phases.

La désintégration $B_{ (s)}$ → τμ est supprimée dans le SM, où le nombre leptonique est conservé. Son observation serait donc une preuve non ambiguë de la physique au-delà du SM. Des résultats récents [1,2] ont ravivé l'intérêt pour la recherche de tels processus [3]. Cette thèse présente la recherche des désintégrations $B_{ (s)}$→ τμ dans l'expérience LHCb, l'une des 4 grandes expériences menées au Large Hadron Collider (LHC) du CERN.Le lepton τ se désintègre avant d'atteindre le détecteur LHCb et est reconstruit en utilisant le canal τ → πππν. Le neutrino provenant de la désintégration du τ échappe à la détection. Une technique de reconstruction spécifique est utilisée pour déduire l'énergie du neutrino et donc la masse invariante du méson B qui s'est désintégré.Afin de séparer le signal du bruit de fond, une sélection hors ligne composée de différentes étapes est appliquée. Des techniques d'analyse multivariées, telles que les arbres de décision boostés (BDT), sont utilisées pendant le processus de sélection.La stratégie d'analyse est complétée par un ajustement simultané à la distribution de masse invariante des mésons B dans différentes régions d'un BDT final. Selon les prédictions du SM, aucun événement de signal n'est attendu. Dans ce cas, la méthode CLs sera utilisée pour extraire les limites supérieures des rapports de branchement BR($B_{ (s)}$→ τμ).[1] Test of lepton universality using $B^+$→$K^+$$l ^+$$l ^-$ decaysPhys. Rev. Lett. 113, 151601 (2014)[2] Measurement of the ratio of branching fractions BR(B → D*τ ν)/BR(B → D*μν)Phys. Rev. Lett. 115 (2015) 111803[3] Lepton Flavour Violation in B Decays ? Phys. Rev. Lett. 114, 091801 (2015) / The decay $B_{ (s)}$→τμ is suppressed in the SM, in which lepton flavour is conserved. Its observation would therefore be an unambiguous evidence of physics beyond the SM. Recent results [1,2] revived the interest for the search of such processes [3]. This thesis presents the search for the $B_{ (s)}$→τμ decays within the LHCb experiment, one of the 4 large experiments operated at the CERN Large Hadron Collider (LHC).The τ lepton decays before reaching the LHCb detector and is reconstructed using the τ→πππν channel. The neutrino from the τ decay escapes detection. A specific reconstruction technique is used in order to infer the energy of the ν and thus the invariant mass of the decaying B meson. This way, the complete kinematics of the process can be solved up to a two fold ambiguity.In order to disentangle signal from background, an offline selection consisting of different steps is applied. Data driven and multivariate analysis techniques, such as Boosted Decision Trees (BDT), are used during the selection process. The analysis strategy is completed by a simultaneous fit to the B meson invariant mass distribution over the different bins of a final BDT. According to the SM expectations, no signal events should be observed. In this case, the CLs method will be used to extract the upper limits on the branching fractions.[1] Test of lepton universality using $B^+$→$K^+$$l ^+$$l ^-$ decaysPhys. Rev. Lett. 113, 151601 (2014)[2] Measurement of the ratio of branching fractions BR(B → D*τ ν)/BR(B → D*μν)Phys. Rev. Lett. 115 (2015) 111803[3] Lepton Flavour Violation in B Decays ? Phys. Rev. Lett. 114, 091801 (2015)

Enquanto todos os modelos com neutrinos massivos de Majorana levam ao mesmo operador efetivo de dimensão d = 5, que não conserva número leptônico, os operadores de dimensão d = 6, obtidos a baixas energias, conservam número leptônico e são diferentes dependendo do modelo de alta energia da nova física. Derivamos os operadores de dimensão d = 6 que são característicos de modelos Seesaw genéricos, no qual a massa do neutrino resulta do intercâmbio de campos pesados que podem ser tanto singletos fermiônicos, tripletos fermiônicos ou tripletos escalares. Os operadores resultantes podem conduzir a efeitos observáveis no futuro próximo, se os coeficientes dos operadores de dimensão d = 5 e d = 6 são desacoplados. Neste trabalho apresentamos o modelo violação mínima de sabor no contexto do modelo seesaw tipo III, no qual é possível obter tal desacoplamento. Isto permite reconstruir a estrutura de sabor a partir dos valores das massas dos neutrino leves e dos parâmetros de mistura, mesmo na presença de fases de violação CP. / While all models of Majorana neutrino masses lead to the same dimension five effective operator, which does not conserve lepton number, the dimension six operators induced at low energies conserve lepton number and differ depending on the high energy model of new physics. We derive the low-energy dimension six operators which are characteristic of generic Seesaw models, in which neutrino masses result from the exchange of heavy fields which may be either fermionic singlets, fermionic triplets or scalar triplets. The resulting operators may lead to effects observable in the near future, if the coefficients of the dimension five and six operators are decoupled. In this work we present the model of minimal avor violation in the context of the type III seesaw model, in which it is possible to obtain the decoupling mentioned before. This allows to reconstruct the avour structure of the model from the values of the light neutrino masses and mixing parameters, even in the presence of CP-violating phases.

It is widely believed that the Standard Model (SM) can not be a fundamental theory of the basic interactions. Originated from this fact, many new physics models have been proposed. Among them, the two Higgs doublet model (2HDM), the SM enlarged by adding one extra scalar doublet, is considered as the simplest extension of the SM. In this work, within the framework of the model III version of the 2HDM, the exclusive decay the branching ratio is calculated and discussed in various physical regions determined by model parameters. It is observed that it is possible to reach present experimental upper limits in model Finally, the avor changing top quark decay,

The lepton flavor violating interactions are interesting in the sense that they are sensitive the physics beyond the standard model and they ensure considerable information about the restrictions of the free parameters, with the help of the possible accurate measurements. In this work, we investigate the lepton flavor violating H+ ! W+l and the lepton flavor conserving H+ ! W+l decays in the general two Higgs doublet model and we estimate decay widths of these decays. After that, we analyze lepton flavor violating decay ! i in the same model and calculate its branching ratio. We observe that the experimental results of the processes under consideration can give comprehensive information about the physics beyond the standard model and the existing free parameters.

The lepton flavor violating interactions are worthwhile to examine since they are sensitive to physics beyond the Standard Model. The simplest extension of the Standard Model promoting the lepton flavor violating interactions are the so called two Higgs doublet model which contains an additional Higgs doublet carrying the same quantum numbers as the first one. In this model, the lepton flavor violating interactions are induced by new scalar Higgs bosons, scalar h^0 and pseudo scalar A^0, and Yukawa couplings, appearing as free parameters, are determined by using the experimental data. On the other hand, the possible extra dimensions are interesting in the sense that they ensure a solution to the hierarchy and cosmological constant problems and also result in the enhancement in the physical quantities of various processes. In the present work, we predict the branching ratios of lepton flavor violating radion decays r-&gt / e^+- mu^-+, r-&gt / e^+- tau^-+ and r-&gt / mu^+- tau^-+ in the two Higgs doublet model, including a single extra dimension, in the framework of the Randall Sundrum scenario. We observed that the branching ratios of the processes we study are at most at the order of 10^-8 for the small values of radion mass and it decreases with the increasing values of the radion mass. Among the LFV decays we study, the r-&gt / mu^+- tau^-+ decay would be the most suitable one to measure its branching ratio.

<p>The ability of the Mu2e experiment to probe, or discover BSM physics in direct CLFV μ+ and π+ decay modes is estimated.</p>

The discovery of the Higgs boson by the LHC provided the last piece of the puzzle neces- sary for the Standard Model (SM) to be a successful theory of electroweak scale physics. However there exist various phenomenological reasons which serve as pointer towards the existence of physics beyond the Standard Model. For example the explanation for the smallness of the neutrino mass, baryon asymmetry of the universe, the presence of dark matter and dark energy etc. are not within purview of the Standard Model. Con- ceptual issues like the gauge hierarchy problem, weakness of gravity provide some of the theoretical motivation to pursue theories beyond the SM. We consider scenarios with warped extra-dimensions (Randall-Sundrum (RS) Model ) as our preferred candidate to answer some of the questions raised above. RS model gives an elegant geometric solution to address the hierarchy between the two fundamental scales of nature i.e. Planck scale and electroweak scale. In addition to this, the geometry of RS serves as a useful setup wherein the fermion mass hierarchy problem can also be solved. The goal of this thesis is to investigate whether RS model can be an acceptable theory of avour while at the same time serving as a solution to the hierarchy problem. In Chapter[1] we begin with a brief introduction of the SM, highlighting issues which pro- vides the necessary motivation for constructing new physics models. Various candidates of Beyond Standard Model (BSM) physics are introduced and a few preliminaries es- sential to understand frameworks with additional spatial-dimensions ( at and warped) is provided. In Chapter[2] we specialize to the case of warped extra-dimensions and motivate the need to have the SM elds in the bulk. Mathematical details related to the analysis of various spin elds (0; 12; 1 and 2) in a warped background necessary to understand relevant phenomenology is provided. The lack of knowledge of Dirac or Majorana nature of the neutrino leads to a wide variety of possibilities as far as neutrino mass generation is concerned. In Chapter[3] we focus on the leptonic sector where three cases of neutrino mass generation are consid- ered: a)Planck Scale lepton number violation (LLHH case) b) Dirac neutrinos c) Bulk Majorana mass terms. We then study the implications of each case on the charged lepton mass tting. The case with Planck scale lepton number violation in normal RS scenario requires large and negative values for the bulk mass parameters for the charged singlets cE. Dirac neutrinos and the case with Bulk Majorana mass terms give good t to data. For completeness, the ts for the hadronic sector is provided in the appendix. In Chapter[4] avour violation for each of three cases introduced in Chapter[3] is studied. For the case with Planck scale lepton number violation, the non-perturbative Yukawa coupling between the SM singlets and the KK states render the higher order diagrams incalculable. Lepton avour violation (LFV) is particularly large for the Dirac case and the bulk Majorana case for low Kaluza-Klein(KK) mass scales. We then invoke the ansatz of Minimal Flavour violation to suppress LFV with low lying KK scales and examples of avour group is provided for both cases. In Chapter[5] we present an example with a type II two Higgs doublet model applied to the LLHH case. The setup o ers a solution where LLHH scenario can be consistently realized in RS model, where the masses and mixing angles in the leptonic sector can bet with O(1) choice of bulk parameters. Assumption of global lepton number conservation (like in Dirac neutrinos) could lead to problems in theories of quantum gravity where it does not hold. This leads us to the question whether Dirac neutrinos can be naturally realized in nature. In Chapter[6] we consider the special case of bulk Majorana mass encountered in Chapter[3] where the bulk Dirac mass terms for the right handed neutrino is set to zero. We nd that this leads to a case where the e ective zero mode neutrino mass is of Dirac type with negligible e ects from the tower of Majorana states. In Chapter[7] we consider RS at the GUT scale which no longer serves as a solution to the hierarchy problem. SUSY is introduced in the bulk and the low energy SUSY serves as a solution to the hierarchy problem. Such models serve as a useful alternative to SUSY models with family symmetries (e.g. Froggatt-Nielsen Model). However the solutions to the Yukawa hierarchy problem are constrained due to anomaly cancellation conditions. In Chapter[8] supersymmetry breaking due to radion mediation in addition to brane localized sources is considered and detailed analysis of the running of soft masses and the low energy avour observables is considered for both cases separately. In Chapter[9] we conclude and present future directions.