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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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De Romeri, V., & Hirsch, M. (2012). Sneutrino dark matter in low-scale seesaw scenarios. J. High Energy Phys., 12(12), 106–28pp.
Abstract: We consider supersymmetric models in which sneutrinos are viable dark matter candidates. These are either simple extensions of the Minimal Supersymmetric Standard Model with additional singlet superfields, such as the inverse or linear seesaw, or a model with an additional U(1) group. All of these models can accomodate the observed small neutrino masses and large mixings. We investigate the properties of sneutrinos as dark matter candidates in these scenarios. We check for phenomenological bounds, such as correct relic abundance, consistency with direct detection cross section limits and laboratory constraints, among others lepton flavour violating (LFV) charged lepton decays. While inverse and linear seesaw lead to different results for LFV, both models have very similar dark matter phenomenology, consistent with all experimental bounds. The extended gauge model shows some additional and peculiar features due to the presence of an extra gauge boson Z' and an additional light Higgs. Specifically, we point out that for sneutrino LSPs there is a strong constraint on the mass of the Z' due to the experimental bounds on the direct detection scattering cross section.
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Deppisch, F. F., Hirsch, M., & Pas, H. (2012). Neutrinoless double-beta decay and physics beyond the standard model. J. Phys. G, 39(12), 124007–23pp.
Abstract: Neutrinoless double-beta decay is the most powerful tool to probe not only for Majorana neutrino masses but for lepton number violating physics in general. We discuss relations between lepton number violation, double-beta decay and neutrino mass, review a general Lorentz-invariant parametrization of the double-beta decay rate, highlight a number of different new physics models showing how different mechanisms can trigger double-beta decay and, finally, discuss possibilities of discriminating and testing these models and mechanisms in complementary experiments.
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Esteves, J. N., Romao, J. C., Hirsch, M., Staub, F., & Porod, W. (2011). Supersymmetric type-III seesaw mechanism: Lepton flavor violating decays and dark matter. Phys. Rev. D, 83(1), 013003–21pp.
Abstract: We study a supersymmetric version of the seesaw mechanism type III. The model consists of the minimal supersymmetric extension of the standard model particle content plus three copies of 24 superfields. The fermionic part of the SU(2) triplet contained in the 24 is responsible for the type-III seesaw, which is used to explain the observed neutrino masses and mixings. Complete copies of 24 are introduced to maintain gauge coupling unification. These additional states change the beta functions of the gauge couplings above the seesaw scale. Using minimal Supergravity boundary conditions, we calculate the resulting supersymmetric mass spectra at the electroweak scale using full 2-loop renormalization group equations. We show that the resulting spectrum can be quite different compared to the usual minimal Supergravity spectrum. We discuss how this might be used to obtain information on the seesaw scale from mass measurements. Constraints on the model space due to limits on lepton flavour violating decays are discussed. The main constraints come from the bounds on μ-> e gamma but there are also regions where the decay tau -> μgamma gives stronger constraints. We also calculate the regions allowed by the dark matter constraint. For the sake of completeness, we compare our results with those for the supersymmetric seesaw type II and, to some extent, with type I.
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Hirsch, M., Reichert, L., & Porod, W. (2011). Supersymmetric mass spectra and the seesaw scale. J. High Energy Phys., 05(5), 086–32pp.
Abstract: Supersymmetric mass spectra within two variants of the seesaw mechanism, commonly known as type-II and type-III seesaw, are calculated using full 2-loop RGEs and minimal Supergravity boundary conditions. The type-II seesaw is realized using one pair of 15 and (15) over bar superfields, while the type-III is realized using three copies of 24(M) superfields. Using published, estimated errors on SUSY mass observables attainable at the LHC and in a combined LHC+ILC analysis, we calculate expected errors for the parameters of the models, most notably the seesaw scale. If SUSY particles are within the reach of the ILC, pure mSugra can be distinguished from mSugra plus type-II or type-III seesaw for nearly all relevant values of the seesaw scale. Even in the case when only the much less accurate LHC measurements are used, we find that indications for the seesaw can be found in favourable parts of the parameter space. Since our conclusions crucially depend on the reliability of the theoretically forecasted error bars, we discuss in some detail the accuracies which need to be achieved for the most important LHC and ILC observables before an analysis, such as the one presented here, can find any hints for type-II or type-III seesaw in SUSY spectra.
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