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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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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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Adolf, P., Hirsch, M., & Päs, H. (2023). Radiative neutrino masses and the Cohen-Kaplan-Nelson bound. J. High Energy Phys., 11(11), 078–14pp.
Abstract: Recently, an increasing interest in UV/IR mixing phenomena has drawn attention to the range of validity of standard quantum field theory. Here we explore the consequences of such a limited range of validity in the context of radiative models for neutrino mass generation. We adopt an argument first published by Cohen, Kaplan and Nelson that gravity implies both UV and IR cutoffs, apply it to the loop integrals describing radiative corrections, and demonstrate that this effect has significant consequences for the parameter space of radiative neutrino mass models.
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Hirsch, M., Lineros, R. A., Morisi, S., Palacio, J., Rojas, N., & Valle, J. W. F. (2013). WIMP dark matter as radiative neutrino mass messenger. J. High Energy Phys., 10(10), 149–18pp.
Abstract: The minimal seesaw extension of the Standard SU(3)(c)circle times SU(2)(L)circle times U(1)(Y) Model requires two electroweak singlet fermions in order to accommodate the neutrino oscillation parameters at tree level. Here we consider a next to minimal extension where light neutrino masses are generated radiatively by two electroweak fermions: one singlet and one triplet under SU(2)(L). These should be odd under a parity symmetry and their mixing gives rise to a stable weakly interactive massive particle (WIMP) dark matter candidate. For mass in the GeV-TeV range, it reproduces the correct relic density, and provides an observable signal in nuclear recoil direct detection experiments. The fermion triplet component of the dark matter has gauge interactions, making it also detectable at present and near future collider experiments.
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Anamiati, G., Hirsch, M., & Nardi, E. (2016). Quasi-Dirac neutrinos at the LHC. J. High Energy Phys., 10(10), 010–19pp.
Abstract: Lepton number violation is searched for at the LHC using same-sign leptons plus jets. The standard lore is that the ratio of same-sign lepton to opposite-sign lepton events, R-ll, is equal to R-ll = 1 (R-ll = 0) for Majorana (Dirac) neutrinos. We clarify under which conditions the ratio Rll can assume values different from 0 and 1, and we argue that the precise value 0 < R-ll < 1 is controlled by the mass splitting versus the width of the quasi-Dirac resonances. A measurement of R-ll not equal 0, 1 would then contain valuable information about the origin of neutrino masses. We consider as an example the inverse seesaw mechanism in a left-right symmetric scenario, which is phenomenologically particularly interesting since all the heavy states in the high energy completion of the model could be within experimental reach. A prediction of this scenario is a correlation between the values of R-ll and the ratio between the rates for heavy neutrino decays into standard model gauge bosons, and into three body final states ljj mediated by off-shell W-R exchange.
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