Arbelaez, C., Carcamo Hernandez, A. E., Cepedello, R., Kovalenko, S., & Schmidt, I. (2020). Sequentially loop suppressed fermion masses from a single discrete symmetry. J. High Energy Phys., 06(6), 043–24pp.
Abstract: We propose a systematic and renormalizable sequential loop suppression mechanism to generate the hierarchy of the Standard Model fermion masses from one discrete symmetry. The discrete symmetry is sequentially softly broken in order to generate one-loop level masses for the bottom, charm, tau and muon leptons and two-loop level masses for the lightest Standard Model charged fermions. The tiny masses for the light active neutrinos are produced from radiative type-I seesaw mechanism, where the Dirac mass terms are effectively generated at two-loop level.
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Centelles Chulia, S., Cepedello, R., Peinado, E., & Srivastava, R. (2019). Systematic classification of two-loop d=4 Dirac neutrino mass models and the Diracness-dark matter stability connection. J. High Energy Phys., 10(10), 093–33pp.
Abstract: We provide a complete systematic classification of all two-loop realizations of the dimension four operator for Dirac neutrino masses. Our classification is multi-layered, starting first with a classification in terms of all possible distinct two loop topologies. Then we discuss the possible diagrams for each topology. Model-diagrams originating from each diagram are then considered. The criterion for genuineness is also defined and discussed at length. Finally, as examples, we construct two explicit models which also serve to highlight the intimate connection between the Dirac nature of neutrinos and the stability of dark matter.
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Bonilla, C., Centelles Chulia, S., Cepedello, R., Peinado, E., & Srivastava, R. (2020). Dark matter stability and Dirac neutrinos using only standard model symmetries. Phys. Rev. D, 101(3), 033011–5pp.
Abstract: We provide a generic framework to obtain stable dark matter along with naturally small Dirac neutrino masses generated at the loop level. This is achieved through the spontaneous breaking of the global U(1)(B-L) symmetry already present in the standard model. The U(1)(B-L) symmetry is broken down to a residual even Z(n) (n >= 4) subgroup. The residual Z(n) symmetry simultaneously guarantees dark matter stability and protects the Dirac nature of neutrinos. The U(1)(B-L) symmetry in our setup is anomaly free and can also be gauged in a straightforward way. Finally, we present an explicit example using our framework to show the idea in action.
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Cepedello, R., Hirsch, M., Rocha-Moran, P., & Vicente, A. (2020). Minimal 3-loop neutrino mass models and charged lepton flavor violation. J. High Energy Phys., 08(8), 067–37pp.
Abstract: We study charged lepton flavor violation for the three most popular 3-loop Majorana neutrino mass models. We call these models “minimal” since their particle content correspond to the minimal sets for which genuine 3-loop models can be constructed. In all the three minimal models the neutrino mass matrix is proportional to some powers of Standard Model lepton masses, providing additional suppression factors on top of the expected loop suppression. To correctly explain neutrino masses, therefore large Yukawa couplings are needed in these models. We calculate charged lepton flavor violating observables and find that the three minimal models survive the current constraints only in very narrow regions of their parameter spaces.
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Cepedello, R., Fonseca, R. M., & Hirsch, M. (2018). Systematic classification of three-loop realizations of the Weinberg operator. J. High Energy Phys., 10(10), 197–34pp.
Abstract: We study systematically the decomposition of the Weinberg operator at three-loop order. There are more than four thousand connected topologies. However, the vast majority of these are infinite corrections to lower order neutrino mass diagrams and only a very small percentage yields models for which the three-loop diagrams are the leading order contribution to the neutrino mass matrix. We identify 73 topologies that can lead to genuine three-loop models with fermions and scalars, i.e. models for which lower order diagrams are automatically absent without the need to invoke additional symmetries. The 73 genuine topologies can be divided into two sub-classes: normal genuine ones (44 cases) and special genuine topologies (29 cases). The latter are a special class of topologies, which can lead to genuine diagrams only for very specific choices of fields. The genuine topologies generate 374 diagrams in the weak basis, which can be reduced to only 30 distinct diagrams in the mass eigenstate basis. We also discuss how all the mass eigenstate diagrams can be described in terms of only five master integrals. We present some concrete models and for two of them we give numerical estimates for the typical size of neutrino masses they generate. Our results can be readily applied to construct other d = 5 neutrino mass models with three loops.
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Cepedello, R., Hirsch, M., & Helo, J. C. (2018). Lepton number violating phenomenology of d=7 neutrino mass models. J. High Energy Phys., 01(1), 009–24pp.
Abstract: We study the phenomenology of d = 7 1-loop neutrino mass models. All models in this particular class require the existence of several new SU(2)(L) multiplets, both scalar and fermionic, and thus predict a rich phenomenology at the LHC. The observed neutrino masses and mixings can easily be fitted in these models. Interestingly, despite the smallness of the observed neutrino masses, some particular lepton number violating (LNV) final states can arise with observable branching ratios. These LNV final states consists of leptons and gauge bosons with high multiplicities, such as 4/ + 4W, 6/ + 2W etc. We study current constraints on these models from upper bounds on charged lepton flavour violating decays, existing lepton number conserving searches at the LHC and discuss possible future LNV searches.
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Cepedello, R., Esser, F., Hirsch, M., & Sanz, V. (2023). SMEFT goes dark: Dark Matter models for four-fermion operators. J. High Energy Phys., 09(9), 081–47pp.
Abstract: We study ultra-violet completions for d = 6 four-fermion operators in the standard model effective field theory (SMEFT), focusing on models that contain cold dark matter candidates. Via a diagrammatic method, we generate systematically lists of possible UV completions, with the aim of providing sets of models, which are complete under certain, well specified assumptions. Within these lists of models we rediscover many known DM models, as diverse as R-parity conserving supersymmetry or the scotogenic neutrino mass model. Our lists, however, also contain many new constructions, which have not been studied in the literature so far. We also briefly discuss how our DM models could be constrained by reinterpretations of LHC searches and the prospects for HL-LHC and future lepton colliders.
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Beltran, R., Cepedello, R., & Hirsch, M. (2023). Tree-level UV completions for NRSMEFT d=6 and d=7 operators. J. High Energy Phys., 08(8), 31pp.
Abstract: We study ultra-violet completions for operators in standard model effective field theory extended with right-handed neutrinos (NRSMEFT). Using a diagrammatic method, we generate systematically lists of possible tree-level completions involving scalars, fermions or vectors for all operators at d = 6 and d = 7, which contain at least one right-handed neutrino. We compare our lists of possible UV models to the ones found for pure SMEFT. We also discuss how the observation of LNV processes via NRSMEFT operators at the LHC can be related to Majorana neutrino masses of the standard model neutrinos.
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