Dib, C., Helo, J. C., Hirsch, M., Kovalenko, S., & Schmidt, I. (2012). Heavy sterile neutrinos in tau decays and the MiniBooNE anomaly. Phys. Rev. D, 85(1), 011301–4pp.
Abstract: Current results of the MiniBooNE experiment show excess events that indicate neutrino oscillations, but only if one goes beyond the standard 3 family scenario. Recently a different explanation of the events has been given, not in terms of oscillations but by the production and decay of a massive sterile neutrino with large transition magnetic moment. We study the effect of such a sterile neutrino in the rare decays tau(-) -> mu(-)mu(+)pi(-)nu and tau(-) -> mu(-)mu(+)e(-)nu nu. We find that searches for these decays, featuring displaced vertices between the mu(-) and the other charged particles, constitute reliable tests for the existence of the sterile neutrino proposed to explain the MiniBooNE anomaly. These searches could be done with already existing experimental data.
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Hirsch, M., Malinsky, M., Porod, W., Reichert, L., & Staub, F. (2012). Hefty MSSM-like light Higgs in extended gauge models. J. High Energy Phys., 02(2), 084.
Abstract: It is well known that in the MSSM the lightest neutral Higgs h(0) must be, at the tree level, lighter than the Z boson and that the loop corrections shift this stringent upper bound up to about 130GeV. Extending the MSSM gauge group in a suitable way, the new Higgs sector dynamics can push the tree-level mass of h(0) well above the tree-level MSSM limit if it couples to the new gauge sector. This effect is further pronounced at the loop level and h(0) masses in the 140GeV ballpark can be reached easily. We exemplify this for a sample setting with a low-scale U(1)(R) x U(1)(B-L) gauge symmetry in which neutrino masses can be implemented via the inverse seesaw mechanism.
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Esteves, J. N., Romao, J. C., Hirsch, M., Porod, W., Staub, F., & Vicente, A. (2012). Dark matter and LHC phenomenology in a left-right supersymmetric model. J. High Energy Phys., 01(1), 095–33pp.
Abstract: Left-right symmetric extensions of the Minimal Supersymmetric Standard Model can explain neutrino data and have potentially interesting phenomenology beyond that found in minimal SUSY seesaw models. Here we study a SUSY model in which the left-right symmetry is broken by triplets at a high scale, but significantly below the GUT scale. Sparticle spectra in this model differ from the usual constrained MSSM expectations and these changes affect the relic abundance of the lightest neutralino. We discuss changes for the standard stau (and stop) co-annihilation, the Higgs funnel and the focus point regions. The model has potentially large lepton flavour violation in both, left and right, scalar leptons and thus allows, in principle, also for flavoured co-annihilation. We also discuss lepton flavour signals due to violating decays of the second lightest neutralino at the LHC, which can be as large as 20 fb(-1) at root s = 14 TeV.
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De Romeri, V., Hirsch, M., & Malinsky, M. (2011). Soft masses in supersymmetric SO(10) GUTs with low intermediate scales. Phys. Rev. D, 84(5), 053012–15pp.
Abstract: The specific shape of the squark, slepton and gaugino mass spectra, if measured with sufficient accuracy, can provide invaluable information not only about the dynamics underpinning their origin at some very high scale such as the unification scale M(G), but also about the intermediate scale physics encountered throughout their renormalization group equations evolution down to the energy scale accessible for the LHC. In this work, we study general features of the TeV scale soft supersymmetry breaking parameters stemming from a generic mSugra configuration within certain classes of supersymmetry SO(10) GUTs with different intermediate symmetries below M(G). We show that particular combinations of soft masses show characteristic deviations from the mSugra limit in different models and thus, potentially, allow to distinguish between these, even if the new intermediate scales are outside the energy range probed at accelerators. We also compare our results to those obtained for the three minimal seesaw models with mSugra boundary conditions and discuss the main differences between those and our SO(10) based models.
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Boucenna, M. S., Hirsch, M., Morisi, S., Peinado, E., Taoso, M., & Valle, J. W. F. (2011). Phenomenology of dark matter from A_4 flavor symmetry. J. High Energy Phys., 05(5), 037–20pp.
Abstract: We investigate a model in which Dark Matter is stabilized by means of a Z(2) parity that results from the same non-abelian discrete flavor symmetry which accounts for the observed patter of neutrino mixing. In our A(4) example the standard model is extended by three extra Higgs doublets and the Z(2) parity emerges as a remnant of the spontaneous breaking of A(4) after electroweak symmetry breaking. We perform an analysis of the parameter space of the model consistent with electroweak precision tests, collider searches and perturbativity. We determine the regions compatible with the observed relic dark matter density and we present prospects for detection in direct as well as indirect Dark Matter search experiments.
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Esteves, J. N., Romao, J. C., Hirsch, M., Vicente, A., Porod, W., & Staub, F. (2010). LHC and lepton flavour violation phenomenology of a left-right extension of the MSSM. J. High Energy Phys., 12(12), 077–44pp.
Abstract: We study the phenomenology of a supersymmetric left-right model, assuming minimal supergravity boundary conditions. Both left-right and (B-L) symmetries are broken at an energy scale close to, but significantly below the GUT scale. Neutrino data is explained via a seesaw mechanism. We calculate the RGEs for superpotential and soft parameters complete at 2-loop order. At low energies lepton flavour violation (LFV) and small, but potentially measurable mass splittings in the charged scalar lepton sector appear, due to the RGE running. Different from the supersymmetric “pure seesaw” models, both, LFV and slepton mass splittings, occur not only in the left-but also in the right slepton sector. Especially, ratios of LFV slepton decays, such as Br((tau) over bar (R) -> μchi(0)(1))/Br((tau) over bar (L) -> μchi(0)(1)) are sensitive to the ratio of (B-L) and left-right symmetry breaking scales. Also the model predicts a polarization asymmetry of the outgoing positrons in the decay mu(+) -> e(+)gamma, A similar to [0, 1], which differs from the pure seesaw “prediction” A = 1. Observation of any of these signals allows to distinguish this model from any of the three standard, pure (mSugra) seesaw setups.
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Hirsch, M., Morisi, S., Peinado, E., & Valle, J. W. F. (2010). Discrete dark matter. Phys. Rev. D, 82(11), 116003–5pp.
Abstract: We propose a new motivation for the stability of dark matter (DM). We suggest that the same non-Abelian discrete flavor symmetry which accounts for the observed pattern of neutrino oscillations, spontaneously breaks to a Z(2) subgroup which renders DM stable. The simplest scheme leads to a scalar doublet DM potentially detectable in nuclear recoil experiments, inverse neutrino mass hierarchy, hence a neutrinoless double beta decay rate accessible to upcoming searches, while theta(13) = 0 gives no CP violation in neutrino oscillations.
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de Campos, F., Eboli, O. J. P., Hirsch, M., Magro, M. B., Porod, W., Restrepo, D., et al. (2010). Probing neutrino oscillations in supersymmetric models at the Large Hadron Collider. Phys. Rev. D, 82(7), 075002–8pp.
Abstract: The lightest supersymmetric particle may decay with branching ratios that correlate with neutrino oscillation parameters. In this case the CERN Large Hadron Collider (LHC) has the potential to probe the atmospheric neutrino mixing angle with sensitivity competitive to its low-energy determination by underground experiments. Under realistic detection assumptions, we identify the necessary conditions for the experiments at CERN's LHC to probe the simplest scenario for neutrino masses induced by minimal supergravity with bilinear R parity violation.
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Hirsch, M., Kernreiter, T., Romao, J. C., & del Moral, A. V. (2010). Minimal supersymmetric inverse seesaw: neutrino masses, lepton flavour violation and LHC phenomenology. J. High Energy Phys., 01(1), 103–21pp.
Abstract: We study neutrino masses in the framework of the supersymmetric inverse seesaw model. Different from the non-supersymmetric version a minimal realization with just one pair of singlets is sufficient to explain all neutrino data. We compute the neutrino mass matrix up to 1-loop order and show how neutrino data can be described in terms of the model parameters. We then calculate rates for lepton flavour violating (LFV) processes, such as μ-> e gamma and chargino decays to singlet scalar neutrinos. The latter decays are potentially observable at the LHC and show a characteristic decay pattern dictated by the same parameters which generate the observed large neutrino angles.
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