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Anamiati, G., Castillo-Felisola, O., Fonseca, R. M., Helo, J. C., & Hirsch, M. (2018). High-dimensional neutrino masses. J. High Energy Phys., 12(12), 066–26pp.
Abstract: For Majorana neutrino masses the lowest dimensional operator possible is the Weinberg operator at d = 5. Here we discuss the possibility that neutrino masses originate from higher dimensional operators. Specifically, we consider all tree-level decompositions of the d = 9, d = 11 and d = 13 neutrino mass operators. With renormalizable interactions only, we find 18 topologies and 66 diagrams for d = 9, and 92 topologies plus 504 diagrams at the d = 11 level. At d = 13 there are already 576 topologies and 4199 diagrams. However, among all these there are only very few genuine neutrino mass models: At d = (9, 11, 13) we find only (2,2,2) genuine diagrams and a total of (2,2,6) models. Here, a model is considered genuine at level d if it automatically forbids lower order neutrino masses without the use of additional symmetries. We also briefly discuss how neutrino masses and angles can be easily fitted in these high-dimensional models.
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Escudero, M., Lopez-Pavon, J., Rius, N., & Sandner, S. (2020). Relaxing cosmological neutrino mass bounds with unstable neutrinos. J. High Energy Phys., 12(12), 119–44pp.
Abstract: At present, cosmological observations set the most stringent bound on the neutrino mass scale. Within the standard cosmological model (Lambda CDM), the Planck collaboration reports Sigma m(v)< 0.12 eV at 95 % CL. This bound, taken at face value, excludes many neutrino mass models. However, unstable neutrinos, with lifetimes shorter than the age of the universe <tau>(nu) less than or similar to t(U), represent a particle physics avenue to relax this constraint. Motivated by this fact, we present a taxonomy of neutrino decay modes, categorizing them in terms of particle content and final decay products. Taking into account the relevant phenomenological bounds, our analysis shows that 2-body decaying neutrinos into BSM particles are a promising option to relax cosmological neutrino mass bounds. We then build a simple extension of the type I seesaw scenario by adding one sterile state nu (4) and a Goldstone boson phi, in which nu (i)-> nu (4)phi decays can loosen the neutrino mass bounds up to Sigma m(v) similar to 1 eV, without spoiling the light neutrino mass generation mechanism. Remarkably, this is possible for a large range of the right-handed neutrino masses, from the electroweak up to the GUT scale. We successfully implement this idea in the context of minimal neutrino mass models based on a U(1)(mu-tau) flavor symmetry, which are otherwise in tension with the current bound on Sigma m(v).
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Miranda, O. G., Papoulias, D. K., Sanders, O., Tortola, M., & Valle, J. W. F. (2021). Low-energy probes of sterile neutrino transition magnetic moments. J. High Energy Phys., 12(12), 191–24pp.
Abstract: Sterile neutrinos with keV-MeV masses and non-zero transition magnetic moments can be probed through low-energy nuclear or electron recoil measurements. Here we determine the sensitivities of current and future searches, showing how they can probe a previously unexplored parameter region. Future coherent elastic neutrino-nucleus scattering (CEvNS) or elastic neutrino-electron scattering (EvES) experiments using a monochromatic 'Cr source can fully probe the region indicated by the recent XENONIT excess.
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Hirsch, M., Joaquim, F. R., & Vicente, A. (2012). Constrained SUSY seesaws with a 125 GeV Higgs. J. High Energy Phys., 11(11), 105–33pp.
Abstract: Motivated by the ATLAS and CMS discovery of a Higgs-like boson with a mass around 125 GeV, and by the need of explaining neutrino masses, we analyse the three canonical SUSY versions of the seesaw mechanism (type I, II and III) with CMSSM boundary conditions. In type II and III cases, SUSY particles are lighter than in the CMSSM (or the constrained type I seesaw), for the same set of input parameters at the universality scale. Thus, to explain m(h0) similar or equal to 125 GeV at low energies, one is forced into regions of parameter space with very large values of m(0), M-1/2 or A(0). We compare the squark and gluino masses allowed by the ATLAS and CMS ranges for m(h0) (extracted from the 2011-2012 data), and discuss the possibility of distinguishing seesaw models in view of future results on SUSY searches. In particular, we briefly comment on the discovery potential of LHC upgrades, for squark/gluino mass ranges required by present Higgs mass constraints. A discrimination between different seesaw models cannot rely on the Higgs mass data alone, therefore we also take into account the MEG upper limit on BR(mu -> e gamma) and show that, in some cases, this may help to restrict the SUSY parameter space, as well as to set complementary limits on the seesaw scale.
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Herrero-Garcia, J., Rius, N., & Santamaria, A. (2016). Higgs lepton flavour violation: UV completions and connection to neutrino masses. J. High Energy Phys., 11(11), 084–45pp.
Abstract: We study lepton violating Higgs (HLFV) decays, first from the effective field theory (EFT) point of view, and then analysing the different high-energy realizations of the operators of the EFT, highlighting the most promising models. We argue why two Higgs doublet models can have a BR(h -> tau mu) similar to 0:01, and why this rate is suppressed in all other realizations including vector-like leptons. We further discuss HLFV in the context of neutrino mass models: in most cases it is generated at one loop giving always BR (h -> tau mu) < 10(-4) and typically much less, which is beyond experimental reach. However, both the Zee model and extended left-right symmetric models contain extra SU(2) doublets coupled to leptons and could in principle account for the observed excess, with interesting connections between HLFV and neutrino parameters.
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