References of "Aristizabal Sierra, Diego"
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See detailShedding Light on the b to s Anomalies
Aristizabal Sierra, Diego ULg; Vicente, Avelino ULg; Staub, Florian

in Physical Review. D, Particles, Fields, Gravitation, and Cosmology (in press)

The LHCb collaboration has recently reported on some anomalies in b→s transitions. In addition to discrepancies with the Standard Model (SM) predictions in some angular observables and branching ratios ... [more ▼]

The LHCb collaboration has recently reported on some anomalies in b→s transitions. In addition to discrepancies with the Standard Model (SM) predictions in some angular observables and branching ratios, an intriguing hint for lepton universality violation was found. Here we propose a simple model that extends the SM with a dark sector charged under an additional U(1) gauge symmetry. The spontaneous breaking of this symmetry gives rise to a massive Z′ boson, which communicates the SM particles with a valid dark matter candidate, while solving the b→s anomalies with contributions to the relevant observables. [less ▲]

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See detailDynamical Flavor Origin of ZN Symmetries
Aristizabal Sierra, Diego ULg; Vicente, Avelino ULg; Fong, Sheng et al

in Physical Review. D, Particles, Fields, Gravitation, and Cosmology (2015), 91(9),

Discrete Abelian symmetries (ZN) are a common “artifact” of beyond the standard model physics models. They provide different avenues for constructing consistent scenarios for lepton and quark mixing ... [more ▼]

Discrete Abelian symmetries (ZN) are a common “artifact” of beyond the standard model physics models. They provide different avenues for constructing consistent scenarios for lepton and quark mixing patterns, radiative neutrino mass generation as well as dark matter stabilization. We argue that these symmetries can arise from the spontaneous breaking of the Abelian U(1) factors contained in the global flavor symmetry transformations of the gauge-invariant kinetic Lagrangian. This will be the case provided the ultraviolet completion responsible for the Yukawa structure involves scalar fields carrying nontrivial U(1) charges. Guided by minimality criteria, we demonstrate the viability of this approach with two examples: first, we derive the “scotogenic” model Lagrangian, and second, we construct a setup where the spontaneous symmetry-breaking pattern leads to a Z3 symmetry which enables dark matter stability as well as neutrino mass generation at the two-loop order. This generic approach can be used to derive many other models, with residual ZN or ZN1×⋯×ZNk symmetries, establishing an intriguing link between flavor symmetries, neutrino masses and dark matter. [less ▲]

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See detailSystematic classification of two-loop realizations of the Weinberg operator
Aristizabal Sierra, Diego ULg; Hirsch, Martin; Degée, Audrey ULg et al

in Journal of High Energy Physics [=JHEP] (2015), 2015(03),

We systematically analyze the d=5 Weinberg operator at 2-loop order. Using a diagrammatic approach, we identify two different interesting categories of neutrino mass models: (i) Genuine 2- loop models for ... [more ▼]

We systematically analyze the d=5 Weinberg operator at 2-loop order. Using a diagrammatic approach, we identify two different interesting categories of neutrino mass models: (i) Genuine 2- loop models for which both, tree-level and 1-loop contributions, are guaranteed to be absent. And (ii) finite 2-loop diagrams, which correspond to the 1-loop generation of some particular vertex appearing in a given 1-loop neutrino mass model, thus being effectively 2-loop. From the large list of all possible 2-loop diagrams, the vast majority are infinite corrections to lower order neutrino mass models and only a moderately small number of diagrams fall into these two interesting classes. Moreover, all diagrams in class (i) are just variations of three basic diagrams, with examples discussed in the literature before. Similarly, we also show that class (ii) diagrams consists of only variations of these three plus two more basic diagrams. Finally, we show how our results can be consistently and readily used in order to construct two-loop neutrino mass models. [less ▲]

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See detailExplaining the CMS Higgs lepton-flavor violating
Aristizabal Sierra, Diego ULg; Vicente, Avelino ULg

in Physical Review. D : Particles and Fields (2014), 90(11), 115004

Direct searches for lepton flavor violating Higgs boson decays in the τ μ channel have been recently reported by the CMS collaboration. The results display a slight excess of signal events with a ... [more ▼]

Direct searches for lepton flavor violating Higgs boson decays in the τ μ channel have been recently reported by the CMS collaboration. The results display a slight excess of signal events with a significance of 2.5σ, which translates into a branching ratio of about 1%. By interpreting these findings as a hint for beyond the standard model physics, we show that the Type-III 2HDM is capable of reproducing such signal while at the same time satisfying vacuum stability, perturbativity, electroweak precision data, measured Higgs standard decay modes and low-energy lepton flavor violating constraints. We have found that the allowed signal strength ranges for the bb, WW* and ZZ* standard channels shrink as soon as BR(h→τμ)∼ 1% is enforced. Thus, we point out that if the excess persists, improved measurements of these channels may be used to test our Type-III 2HDM scenario. [less ▲]

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See detailScalar triplet flavored leptogenesis: a systematic approach
Aristizabal Sierra, Diego ULg; Dhen, Mikael; Hambye, Thomas

in Journal of Cosmology and Astroparticle Physics [= JCAP] (2014), 2014

Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed ... [more ▼]

Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed neutrinos or extra triplets, it also provides a compelling framework for baryogenesis via leptogenesis. We derive in this context the full network of Boltzmann equations for studying leptogenesis in the flavored regime. To this end we determine the relations which hold among the chemical potentials of the various particle species in the thermal bath. This takes into account the standard model Yukawa interactions of both leptons and quarks as well as sphaleron processes which, depending on the temperature, may be classified as faster or slower than the Universe Hubble expansion. We find that when leptogenesis is enabled by the presence of an extra triplet, lepton flavor effects allow the production of the B-L asymmetry through lepton number conserving CP asymmetries. This scenario becomes dominant as soon as the triplets couple more to leptons than to standard model scalar doublets. In this case, the way the B-L asymmetry is created through flavor effects is novel: instead of invoking the effect of L-violating inverse decays faster than the Hubble rate, it involves the effect of L-violating inverse decays slower than the Hubble rate. We also analyze the more general situation where lepton number violating CP asymmetries are present and actively participate in the generation of the B-L asymmetry, pointing out that as long as L-violating triplet decays are still in thermal equilibrium when the triplet gauge scattering processes decouple, flavor effects can be striking, allowing to avoid all washout suppression effects from seesaw interactions. In this case the amount of B-L asymmetry produced is limited only by a universal gauge suppression effect, which nevertheless goes away for large triplet decay rates. [less ▲]

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See detailReactor mixing angle from hybrid neutrino masses
Aristizabal Sierra, Diego ULg; de Medeiros Varzielas, Ivo

in Journal of High Energy Physics [=JHEP] (2014), 2014(7),

In terms of its eigenvector decomposition, the neutrino mass matrix (in the basis where the charged lepton mass matrix is diagonal) can be understood as originating from a tribimaximal dominant structure ... [more ▼]

In terms of its eigenvector decomposition, the neutrino mass matrix (in the basis where the charged lepton mass matrix is diagonal) can be understood as originating from a tribimaximal dominant structure with small deviations, as demanded by data. If neutrino masses originate from at least two different mechanisms, referred to as "hybrid neutrino masses", the experimentally observed structure naturally emerges provided one mechanism accounts for the dominant tribimaximal structure while the other is responsible for the deviations. We demonstrate the feasibility of this picture in a fairly model-independent way by using lepton-number-violating effective operators, whose structure we assume becomes dictated by an underlying A4 flavor symmetry. We show that if a second mechanism is at work, the requirement of generating a reactor angle within its experimental range always fixes the solar and atmospheric angles in agreement with data, in contrast to the case where the deviations are induced by next-to-leading order effective operators. We prove this idea is viable by constructing an A4-based ultraviolet completion, where the dominant tribimaximal structure arises from the type-I seesaw while the subleading contribution is determined by either type-II or type-III seesaw driven by a non-trivial A4 singlet (minimal hybrid model). After finding general criteria, we identify all the ZN symmetries capable of producing such A4-based minimal hybrid models. [less ▲]

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See detailCloistered Baryogenesis
Aristizabal Sierra, Diego ULg; Fong, Chee Sheng; Nardi, Enrico et al

in Journal of Cosmology and Astroparticle Physics [= JCAP] (2014), 2014

The cosmological matter-antimatter asymmetry can arise from the baryon number conserving CP asymmetry in two body decays of heavy particles, when the two final states carry equal and opposite baryon ... [more ▼]

The cosmological matter-antimatter asymmetry can arise from the baryon number conserving CP asymmetry in two body decays of heavy particles, when the two final states carry equal and opposite baryon number, and one couples directly or indirectly to electroweak sphalerons so that its baryon asymmetry gets partly reprocessed into a lepton asymmetry, while the other remains chemically decoupled from the thermal bath with its baryon content frozen. After sphaleron switchoff the decay of the decoupled particles inject in the thermal plasma an unbalanced baryon asymmetry, giving rise to baryogenesis. We highlight the features of this mechanism in a type-I seesaw model extended by adding a new colored scalar coupled to the heavy Majorana neutrinos. If the colored scalar has an O(TeV) mass, it would leave at the LHC a characteristic signature throughout all layers of the detectors. [less ▲]

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See detailLeptogenesis with a dynamical seesaw scale
Aristizabal Sierra, Diego ULg; Tortola, Maria; Valle, Jose et al

in Journal of Cosmology and Astroparticle Physics [= JCAP] (2014), 2014

In the simplest type-I seesaw leptogenesis scenario right-handed neutrino annihilation processes are absent. However, in the presence of new interactions these processes are possible and can affect the ... [more ▼]

In the simplest type-I seesaw leptogenesis scenario right-handed neutrino annihilation processes are absent. However, in the presence of new interactions these processes are possible and can affect the resulting B-L asymmetry in an important way. A prominent example is provided by models with spontaneous lepton number violation, where the existence of new dynamical degrees of freedom can play a crucial role. In this context, we provide a model-independent discussion of the effects of right-handed neutrino annihilations. We show that in the weak washout regime, as long as the scattering processes remain slow compared with the Hubble expansion rate throughout the relevant temperature range, the efficiency can be largely enhanced, reaching in some cases maximal values. Moreover, the B-L asymmetry yield turns out to be independent upon initial conditions, in contrast to the ''standard'' case. On the other hand, when the annihilation processes are fast, the right-handed neutrino distribution tends to a thermal one down to low temperatures, implying a drastic suppression of the efficiency which in some cases can render the B-L generation mechanism inoperative. [less ▲]

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See detailLSP sneutrino decays
Aristizabal Sierra, Diego ULg; Restrepo, Diego; Spinner, Sogee

in Journal of High Energy Physics [=JHEP] (2013), 1305

In bilinear R-parity violation (BRpV), in which the superpotential includes a bilinear term between the lepton doublet and the up-type Higgs superfields, a sneutrino LSP can decay into pairs of heavy ... [more ▼]

In bilinear R-parity violation (BRpV), in which the superpotential includes a bilinear term between the lepton doublet and the up-type Higgs superfields, a sneutrino LSP can decay into pairs of heavy standard model states: W's, Z's, tops or Higgs bosons. These finals states can dominate over the traditionally considered bottom pair final state. This would lead to unique and novel supersymmetric signals with each supersymmetric event possibly producing two pairs of these heavy standard model fields. We investigate this possibility and find that the branching ratio into heavier states dominates when the bilinear term is much smaller than the sneutrino vacuum expectation value for a given sneutrino flavor. When BRpV is the only source of neutrino masses these decays can only dominate for one of the sneutrino generations. Relaxing this constraint opens these channels for all three generations. [less ▲]

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See detailScalar triplet leptogenesis without right-handed neutrino decoupling
Aristizabal Sierra, Diego ULg

in Nuclear Physics B Proceedings Supplement (2013, April), 237-238

We discuss leptogenesis in the context of type-II seesaw in the case in which in addition to the scalar electroweak triplet decays the lepton asymmetry is also induced by right-handed neutrino decays ... [more ▼]

We discuss leptogenesis in the context of type-II seesaw in the case in which in addition to the scalar electroweak triplet decays the lepton asymmetry is also induced by right-handed neutrino decays (mild hierarchical scenarios). We show that within this setup, depending on the relative sizes of the relevant parameters, one can identify three classes of generic models, each one with its own consequences for leptogenesis. [less ▲]

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See detailEigenvector-based approach to neutrino mixing
Aristizabal Sierra, Diego ULg; Houet, Eric; Ivo, Medeiros Varzielas

in Physical Review. D, Particles, Fields, Gravitation, and Cosmology (2013), 87

We propose a model-independent analysis of the neutrino mass matrix through an expansion in terms of the eigenvectors defining the lepton mixing matrix, which we show can be parametrized as small ... [more ▼]

We propose a model-independent analysis of the neutrino mass matrix through an expansion in terms of the eigenvectors defining the lepton mixing matrix, which we show can be parametrized as small perturbations of the tribimaximal mixing eigenvectors. This approach proves to be powerful and convenient for some aspects of lepton mixing, in particular when studying the sensitivity of the mass matrix elements to departures from their tribimaximal form. In terms of the eigenvector decomposition, the neutrino mass matrix can be understood as originating from a tribimaximal dominant structure with small departures determined by data. By implementing this approach to cases when the neutrino masses originate from different mechanisms, we show that the experimentally observed structure arises very naturally. We thus claim that the observed deviations from the tribimaximal mixing pattern might be interpreted as a possible hint of a ``hybrid'' nature of the neutrino mass matrix. [less ▲]

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See detailLepton flavor violation and seesaw symmetries
Aristizabal Sierra, Diego ULg

in Hyperfine Interactions (2013, February), 214

When the standard model is extended with right-handed neutrinos the symmetries of the resulting Lagrangian are enlarged with a new global U(1)R Abelian factor. In the context of minimal seesaw models we ... [more ▼]

When the standard model is extended with right-handed neutrinos the symmetries of the resulting Lagrangian are enlarged with a new global U(1)R Abelian factor. In the context of minimal seesaw models we analyze the implications of a slightly broken U(1)R symmetry on charged lepton flavor violating decays. We find, depending on the R-charge assignments, models where charged lepton flavor violating rates can be within measurable ranges. In particular, we show that in the resulting models due to the structure of the light neutrino mass matrix muon flavor violating decays are entirely determined by neutrino data (up to a normalization factor) and can be sizable in a wide right-handed neutrino mass range. [less ▲]

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See detailThe role of lepton flavor symmetries in leptogenesis
Aristizabal Sierra, Diego ULg; De Medeiros Varzielas, Ivo

in Fortschritte der Physik = Progress of Physics (2013), 61(4-5),

The presence of flavor symmetries in the lepton sector may have several consequences for the generation of the baryon asymmetry of the Universe via leptogenesis. We review the mechanism in general type-I ... [more ▼]

The presence of flavor symmetries in the lepton sector may have several consequences for the generation of the baryon asymmetry of the Universe via leptogenesis. We review the mechanism in general type-I, type-II and type-III seesaw models. We then turn to the discussion of the cases when the asymmetry is generated in the context of seesaw models extended with flavor symmetries, before or after flavor symmetry breaking. Finally we explain how the interplay between type-I and type-II seesaws can (or not) lead to viable models for leptogenesis even when there is an exact mixing pattern enforced by the flavor symmetry. [less ▲]

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See detailLeptogenesis in flavor models with type I and II seesaws
Aristizabal Sierra, Diego ULg; Bazzocchi, Federica; de Medeiros Varzielas, Ivo

in Nuclear Physics B (2012), 858

In type I seesaw models with flavor symmetries accounting for the lepton mixing angles the CP asymmetry in right-handed neutrino decays vanishes in the limit in which the mixing pattern is exact. We study ... [more ▼]

In type I seesaw models with flavor symmetries accounting for the lepton mixing angles the CP asymmetry in right-handed neutrino decays vanishes in the limit in which the mixing pattern is exact. We study the implications that additional degrees of freedom from type II seesaw may have for leptogenesis in such a limit. We classify in a model independent way the possible realizations of type I and II seesaw schemes, differentiating between classes in which leptogenesis is viable or not. We point out that even with the interplay of type I and II seesaws there are generic classes of minimal models in which the CP asymmetry vanishes. Finally we analyze the generation of the lepton asymmetry by solving the corresponding kinetic equations in the general case of a mild hierarchy between the light right-handed neutrino and the scalar triplet masses. We identify the possible scenarios in which leptogenesis can take place. [less ▲]

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See detailMinimal Lepton Flavor Violating Realizations of Minimal Seesaw Models.
Aristizabal Sierra, Diego ULg; Degée, Audrey ULg; Kamenik, Jernej F.

in Journal of High Energy Physics [=JHEP] (2012), JHEP 1207 (2012) 135(2012), 135-156

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 ... [more ▼]

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 identi fied. 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 fi rst 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->e \gamma , \mu->3e and \mu- 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 eff ects of the right- handed neutrino interactions on primordial B- L asymmetries,fi nding 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. [less ▲]

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See detailLeptogenesis in the presence of exact flavor symmetries
Aristizabal Sierra, Diego ULg; Bazzocchi, Federica

in Journal of High Energy Physics [=JHEP] (2012)

In models with flavor symmetries in the leptonic sector leptogenesis can take place in a very different way compared to the standard leptogenesis scenario. We study the generation of a B−L asymmetry in ... [more ▼]

In models with flavor symmetries in the leptonic sector leptogenesis can take place in a very different way compared to the standard leptogenesis scenario. We study the generation of a B−L asymmetry in these kind of models in the flavor symmetric phase pointing out that successful leptogenesis requires (i) the right-handed neutrinos to lie in different irreducible representations of the flavor group; (ii) the flavons to be lighter at least that one of the right-handed neutrino representations. When these conditions are satisfied leptogenesis proceeds due to new contributions to the CP violating asymmetry and — depending on the specific model — in several stages. We demonstrate the validity of these arguments by studying in detail the generation of the B − L asymmetry in a scenario of a concrete A 4 flavor model realization. [less ▲]

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See detailOn the importance of the 1-loop finite corrections to seesaw neutrino masses.
Aristizabal Sierra, Diego ULg; Yaguna, Carlos

in Journal of High Energy Physics [=JHEP] (2011)

In the standard seesaw mechanism, finite corrections to the neutrino mass matrix arise from 1-loop self-energy diagrams mediated by a heavy neutrino. We study in detail these corrections and demonstrate ... [more ▼]

In the standard seesaw mechanism, finite corrections to the neutrino mass matrix arise from 1-loop self-energy diagrams mediated by a heavy neutrino. We study in detail these corrections and demonstrate that they can be very significant, exceeding in several cases the tree-level result. We consider the normal and inverted hierarchy spectra for light neutrinos and compute the finite corrections to the different elements of the neutrino mass matrix. Special attention is paid to their dependence with the parameters of the seesaw model. Among the cases in which the corrections can be large, we identify the fine-tuned models considered previously in the literature, where a strong cancellation between the different parameters is required to achieve compatibility with the experimental data. As a particular example, we also analyze how these corrections modify the tribimaximal mixing pattern and find that the deviations may be sizable, in particular for θ13. Finally, we emphasize that due to their large size, the finite corrections to neutrino masses have to be taken into account if one wants to properly scan the parameter space of seesaw models. [less ▲]

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See detailNeutrino masses beyond the tree level
Aristizabal Sierra, Diego ULg

in Few-Body Systems (2011, July)

Models for Majorana neutrino masses can be classified according to the level in perturbation theory at which the effective dimension five operator LLHH is realized. The possibilities range from the tree ... [more ▼]

Models for Majorana neutrino masses can be classified according to the level in perturbation theory at which the effective dimension five operator LLHH is realized. The possibilities range from the tree-level up to the three-loop level realizations. We discuss some general aspects of this approach and speculate about a model independent classification of the possible cases. Among all the realizations, those in which the effective operator is induced by radiative corrections open the possibility for lepton number violation near -or at- the electroweak scale. We discuss some phenomenological aspects of two generic radiative realizations: the Babu-Zee model and supersymmetric models with bilinear R-parity violation. [less ▲]

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See detailImplications of tribimaximal lepton mixing for leptogenesis
Aristizabal Sierra, Diego ULg

Conference (2011, July)

In models featuring exact mixing patterns the mass matrices that define the effective light neutrino mass matrix -and the light neutrino matrix itself- are form-diagonalizable. We study leptogenesis in ... [more ▼]

In models featuring exact mixing patterns the mass matrices that define the effective light neutrino mass matrix -and the light neutrino matrix itself- are form-diagonalizable. We study leptogenesis in type I seesaw models in these contexts pointing out that the CP asymmetry in right-handed neutrino decays vanishes as a consequence of the mass matrices being form-diagonalizable. A non-vanishing CP asymmetry arises once deviations from the exact mixing scheme, induced by higher order effective operators, is allowed. Finally we discuss alternative pathways to viable leptogenesis in these kind of models. [less ▲]

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See detailOne-loop finite corrections to seesaw neutrino masses
Aristizabal Sierra, Diego ULg

in PoS - Proceedings of Science (2011)

In the standard seesaw model, finite corrections to the neutrino mass matrix arise from one-loop self-energy diagrams mediated by heavy neutrinos. We discuss the impact that these corrections may have on ... [more ▼]

In the standard seesaw model, finite corrections to the neutrino mass matrix arise from one-loop self-energy diagrams mediated by heavy neutrinos. We discuss the impact that these corrections may have on the different entries of the tree-level effective neutrino mass matrix, paying special attention to their dependence with the seesaw model parameters. We also briefly comment on the implications these corrections might have on low-energy neutrino observables. [less ▲]

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