Neutrino masses and their implications for low energy experiments and the LHC

Neutrino oscillations constitute the first experimental evidence of new physics. Con- trary to the prediction of the Standard Model, neutrinos are now well-established as particles with mass. In this thesis we study four topics related to neutrino masses. We examine a class of patterns of Majorana neutrino mass matrices, called two-zero textures, that could lead to the building of the underlying flavour theory. Using a purely numerical technique, we compare the constraints given by the textures with the most updated data of oscillation parameters. We find that the most promising textures are those of class A with normal ordering. Further, we revisit the case of excluded textures and study the stability of the results when the textures are only approximate. Then, we present a new model of neutrino masses that is able to generate an A class texture. Due to the form of the mass matrix, the standard neutrino exchange mechanism is suppressed; however, a neutrinoless double beta decay rate large enough to be tested in the near future is induced through a short range mechanism. Moreover, this model belongs to a broad variety of frameworks that are based on the interaction of a lepton number violating charged scalar with light leptons. The signatures of such scalars, often accompanied by missing energy, are not currently being probed at high-energy accelerators. We propose a search strategy and examine the prospects for their signatures at the Large Hadron Col- lider. Finally, we consider the possibility that neutrinos are Dirac particles. In this context, right-handed neutrinos need to be properly included in the effective field theory of the Standard Model. Some of the resulting effective operators would show interesting phenomenological impact that can be addressed with current experimen- tal data. Furthermore, our results would indicate how further investigations should be designed in the future in order to test the unbounded operators to shed light on possible new physics. Accordingly, we propose a new search in the context of rare top decays

LHC sensitivity to singly charged scalars decaying into electrons and muons

Current LHC searches for nonsupersymmetric singly charged scalars, based on two-Higgs-doublet models, in general, focus the analysis in third-generation fermions in the final state. However, singly charged scalars in alternative extensions of the scalar sector involve Yukawa couplings not proportional to the mass of the fermions. Assuming the scalar decays into electrons and muons, it can manifest cleaner experimental signatures. In this paper, we suggest that a singly charged scalar singlet, with electroweak production, can start to be probed in the near future with dedicated search strategies. Depending on the strength of the Yukawa couplings, two independent scenarios are considered: direct pair production (small couplings) and single production via a virtual neutrino exchange (large couplings). We show that, up to a mass as large as 500 GeV, most of the parameter space could be excluded at the 95% C.L. in a high-luminosity phase of the LHC. Our results also apply to other frameworks, provided the singly charged scalar exhibits similar production patterns and dominant decay modes.Instituto de Física La Plat

Fitting flavour symmetries: the case of two-zero neutrino mass textures

We present a numeric method for the analysis of the fermion mass matrices predicted in flavour models. The method does not require any previous algebraic work, it offers a χ2 comparison test and an easy estimate of confidence intervals. It can also be used to study the stability of the results when the predictions are disturbed by small perturbations. We have applied the method to the case of two-zero neutrino mass textures using the latest available fits on neutrino oscillations, derived the available parameter space for each texture and compared them. Textures A1 and A2 seem favoured because they give a small χ2, allow for large regions in parameter space and give neutrino masses compatible with Cosmology limits. The other 'allowed' textures remain allowed although with a very constrained parameter space, which, in some cases, could be in conflict with Cosmology. We have also revisited the 'forbidden' textures and studied the stability of the results when the texture zeroes are not exact. Most of the forbidden textures remain forbidden, but textures F1 and F3 are particularly sensitive to small perturbations and could become allowed

LHC signals of radiatively-induced neutrino masses and implications for the Zee-Babu model

Contrary to the see-saw models, extended Higgs sectors leading to radiatively-induced neutrino masses do require the extra particles to be at the TeV scale. However, these new states have often exotic decays, to which experimental LHC searches performed so far, focused on scalars decaying into pairs of same-sign leptons, are not sensitive. In this paper we show that their experimental signatures can start to be tested with current LHC data if dedicated multi-region analyses correlating different observables are used. We also provide high-accuracy estimations of the complicated Standard Model backgrounds involved. For the case of the Zee-Babu model, we show that regions not yet constrained by neutrino data and low-energy experiments can be already probed, while most of the parameter space could be excluded at the 95% C.L. in a high-luminosity phase of the LHC

Mapping recent information behavior research: an analysis of co-authorship and cocitation networks

There has been an increase in research published on information behavior in recent years, and this has been accompanied by an increase in its diversity and interaction with other fields, particularly information retrieval (HR). The aims of this study are to determine which researchers have contributed to producing the current body of knowledge on this subject, and to describe its intellectual basis. A bibliometric and network analysis was applied to authorship and co-authorship as well as citation and co-citation. According to these analyses, there is a small number of authors who can be considered to be the most productive and who publish regularly, and a large number of transient ones. Other findings reveal a marked predominance of theoretical works, some examples of qualitative methodology that originate in other areas of social science, and a high incidence of research focused on the user interaction with information retrieval systems and the information behavior of doctors

A model of neutrino mass and dark matter with large neutrinoless double beta decay

We propose a model where neutrino masses are generated at three loop order but neutrinoless double beta decay occurs at one loop. Thus we can have large neutrinoless double beta decay observable in the future experiments even when the neutrino masses are very small. The model receives strong constraints from the neutrino data and lepton flavor violating decays, which substantially reduces the number of free parameters. Our model also opens up the possibility of having several new scalars below the TeV regime, which can be explored at the collider experiments. Additionally, our model also has an unbroken Z2 symmetry which allows us to identify a viable Dark Matter candidate

Neutrino masses and their implications for low energy experiments and the LHC

Neutrino oscillations constitute the first experimental evidence of new physics. Con- trary to the prediction of the Standard Model, neutrinos are now well-established as particles with mass. In this thesis we study four topics related to neutrino masses. We examine a class of patterns of Majorana neutrino mass matrices, called two-zero textures, that could lead to the building of the underlying flavour theory. Using a purely numerical technique, we compare the constraints given by the textures with the most updated data of oscillation parameters. We find that the most promising textures are those of class A with normal ordering. Further, we revisit the case of excluded textures and study the stability of the results when the textures are only approximate. Then, we present a new model of neutrino masses that is able to generate an A class texture. Due to the form of the mass matrix, the standard neutrino exchange mechanism is suppressed; however, a neutrinoless double beta decay rate large enough to be tested in the near future is induced through a short range mechanism. Moreover, this model belongs to a broad variety of frameworks that are based on the interaction of a lepton number violating charged scalar with light leptons. The signatures of such scalars, often accompanied by missing energy, are not currently being probed at high-energy accelerators. We propose a search strategy and examine the prospects for their signatures at the Large Hadron Col- lider. Finally, we consider the possibility that neutrinos are Dirac particles. In this context, right-handed neutrinos need to be properly included in the effective field theory of the Standard Model. Some of the resulting effective operators would show interesting phenomenological impact that can be addressed with current experimen- tal data. Furthermore, our results would indicate how further investigations should be designed in the future in order to test the unbounded operators to shed light ..

LHC sensitivity to singly charged scalars decaying into electrons and muons

Current LHC searches for nonsupersymmetric singly charged scalars, based on two-Higgs-doublet models, in general, focus the analysis in third-generation fermions in the final state. However, singly charged scalars in alternative extensions of the scalar sector involve Yukawa couplings not proportional to the mass of the fermions. Assuming the scalar decays into electrons and muons, it can manifest cleaner experimental signatures. In this paper, we suggest that a singly charged scalar singlet, with electroweak production, can start to be probed in the near future with dedicated search strategies. Depending on the strength of the Yukawa couplings, two independent scenarios are considered: direct pair production (small couplings) and single production via a virtual neutrino exchange (large couplings). We show that, up to a mass as large as 500 GeV, most of the parameter space could be excluded at the 95% C.L. in a high-luminosity phase of the LHC. Our results also apply to other frameworks, provided the singly charged scalar exhibits similar production patterns and dominant decay modes

Probes of the Standard Model effective field theory extended with a right-handed neutrino

If neutrinos are Dirac particles and, as suggested by the so far null LHC results, any new physics lies at energies well above the electroweak scale, the Standard Model effective field theory has to be extended with operators involving the right-handed neutrinos. In this paper, we study this effective field theory and set constraints on the different dimension-six interactions. To that aim, we use LHC searches for associated production of light (and tau) leptons with missing energy, monojet searches, as well as pion and tau decays. Our bounds are generally above the TeV for order one couplings. One particular exception is given by operators involving top quarks. These provide new signals in top decays not yet studied at colliders. Thus, we also design an LHC analysis to explore these signatures in the tt¯ production. Our results are also valid if the right-handed neutrinos are Majorana and lon