Ghosh, P., Lara, I., Lopez-Fogliani, D. E., Muñoz, C., & Ruiz de Austri, R. (2018). Searching for left sneutrino LSP at the LHC. Int. J. Mod. Phys. A, 33(18-19), 1850110–62pp.
Abstract: We analyze relevant signals expected at the LHC for a left sneutrino as the lightest supersymmetric particle (LSP). The discussion is carried out in the “mu from nu” supersymmetric standard model (mu nu SSM), where the presence of R-parity breaking couplings involving right-handed neutrinos solves the μproblem and reproduces neutrino data. The sneutrinos are pair produced via a virtual W, Z or gamma in the s channel. From the prompt decay of a pair of left sneutrinos LSPs of any family, a significant diphoton signal plus missing transverse energy (MET) from neutrinos can be present in the mass range 118-132 GeV, with 13 TeV center-of-mass energy and an integrated luminosity of 100 fb(-1). In addition, in the case of a pair of tau left sneutrinos LSPs, given the large value of the tau Yukawa coupling diphoton plus leptons and/or multileptons can appear. We find that the number of expected events for the multilepton signal, together with properly adopted search strategies, is sufficient to give a significant evidence for a sneutrino of mass in the range 130-310 GeV, even with the integrated luminosity of 20 fb(-1). In the case of the signal producing diphoton plus leptons, an integrated luminosity of 100 fb(-1) is needed to give a significant evidence in the mass range 95-145 GeV. Finally, we discuss briefly the presence of displaced vertices and the associated range of masses.
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Feruglio, F., Gherardi, V., Romanino, A., & Titov, A. (2021). Modular invariant dynamics and fermion mass hierarchies around tau = i. J. High Energy Phys., 05(5), 242–26pp.
Abstract: We discuss fermion mass hierarchies within modular invariant flavour models. We analyse the neighbourhood of the self-dual point tau = i, where modular invariant theories possess a residual Z(4) invariance. In this region the breaking of Z(4) can be fully described by the spurion epsilon approximate to tau – i, that flips its sign under Z(4). Degeneracies or vanishing eigenvalues of fermion mass matrices, forced by the Z(4) symmetry at tau = i, are removed by slightly deviating from the self-dual point. Relevant mass ratios are controlled by powers of vertical bar epsilon vertical bar. We present examples where this mechanism is a key ingredient to successfully implement an hierarchical spectrum in the lepton sector, even in the presence of a non-minimal Kahler potential.
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Beneke, M., Hellmann, C., & Ruiz-Femenia, P. (2015). Heavy neutralino relic abundance with Sommerfeld enhancements – a study of pMSSM scenarios. J. High Energy Phys., 03(3), 162–37pp.
Abstract: We present a detailed discussion of Sommerfeld enhancements in neutralino dark matter relic abundance calculations for several popular benchmark scenarios in the general MSSM. Our analysis is focused on models with heavy wino- and higgsino-like neutralino LSI' and models interpolating between these two scenarios. This work is the first phenomenological application of effective field theory methods that we have developed in earlier work and that allow for the consistent study of Sommerfeld enhancements in nonrelativistic neutralino and chargino co-annihilation reactions within the general MSSM, away from the pure-wino and pure-higgsino limits.
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Lopez-Ibañez, M. L., Melis, A., Jay Perez, M., & Vives, O. (2017). Slepton non-universality in the flavor-effective MSSM. J. High Energy Phys., 11(11), 162–27pp.
Abstract: Supersymmetric theories supplemented by an underlying flavor-symmetry G(f) provide a rich playground for model building aimed at explaining the flavor structure of the Standard Model. In the case where supersymmetry breaking is mediated by gravity, the soft-breaking Lagrangian typically exhibits large tree-level flavor violating e ff ects, even if it stems from an ultraviolet flavor-conserving origin. Building on previous work, we continue our phenomenological analysis of these models with a particular emphasis on leptonicflavor observables. We consider three representative models which aim to explain the flavor structure of the lepton sector, with symmetry groups G(f) = Delta (27), A(4); and S-3.
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Beneke, M., Hellmann, C., & Ruiz-Femenia, P. (2013). Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos I. General framework and S-wave annihilation. J. High Energy Phys., 03(3), 148–48pp.
Abstract: We compute analytically the tree-level annihilation rates of a collection of non-relativistic neutralino and chargino two-particle states in the general MSSM, including the previously unknown off-diagonal rates. The results are prerequisites to the calculation of the Sommerfeld enhancement in the MSSM, which will be presented in subsequent work. They can also be used to obtain concise analytic expressions for MSSM dark matter pair annihilation in the present Universe for a large number of exclusive two-particle final states.
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Bustamante, M., Gago, A. M., & Jones Perez, J. (2011). SUSY renormalization group effects in ultra high energy neutrinos. J. High Energy Phys., 05(5), 133–26pp.
Abstract: We have explored the question of whether the renormalization group running of the neutrino mixing parameters in the Minimal Supersymmetric Standard Model is detectable with ultra-high energy neutrinos from active galactic nuclei (AGN). We use as observables the ratios of neutrino fluxes produced at the AGN, focusing on four different neutrino production models: (Phi(0)(v epsilon+(v) over bar epsilon) : Phi(0)(v mu+(v) over bar mu) : Phi(0)(v tau+(v) over bar tau)) = (1 : 2 : 0), (0 : 1 : 0), (1 : 0 : 0), and (1 : 1 : 0). The prospects for observing deviations experimentally are taken into consideration, and we find out that it is necessary to impose a cut-off on the transferred momentum of Q(2) >= 10(7) GeV(2). However, this condition, together with the expected low value of the diffuse AGN neutrino flux, yields a negligible event rate at a km-scale. Cerenkov detector such as IceCube.
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Cabrera, M. E., Casas, J. A., Mitsou, V. A., Ruiz de Austri, R., & Terron, J. (2012). Histogram comparison tools for the search of new physics at LHC. Application to the CMSSM. J. High Energy Phys., 04(4), 133–27pp.
Abstract: We propose a rigorous and effective way to compare experimental and theoretical histograms, incorporating the different sources of statistical and systematic uncertainties. This is a useful tool to extract as much information as possible from the comparison between experimental data with theoretical simulations, optimizing the chances of identifying New Physics at the LHC. We illustrate this by showing how a search in the CMSSM parameter space, using Bayesian techniques, can effectively find the correct values of the CMSSM parameters by comparing histograms of events with multijets + missing transverse momentum displayed in the effective-mass variable. The procedure is in fact very efficient to identify the true supersymmetric model, in the case supersymmetry is really there and accessible to the LHC.
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Beneke, M., Hellmann, C., & Ruiz-Femenia, P. (2015). Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos III. Computation of the Sommerfeld enhancements. J. High Energy Phys., 05(5), 115–57pp.
Abstract: This paper concludes the presentation of the non-relativistic effective field theory formalism designed to calculate the radiative corrections that enhance the pair-annihilation cross sections of slowly moving neutralinos and charginos within the general minimal supersymmetric standard model (MSSM). While papers I and II focused on the computation of the tree-level annihilation rates that feed into the short-distance part, here we describe in detail the method to obtain the Sommerfeld factors that contain the enhanced long-distance corrections. This includes the computation of the potential interactions in the MSSM, which are provided in compact analytic form, and a novel solution of the multi-state Schrodinger equation that is free from the numerical instabilities generated by large mass splittings between the scattering states. Our results allow for a precise computation of the MSSM neutralino dark matter relic abundance and pair-annihilation rates in the present Universe, when Sommerfeld enhancements are important.
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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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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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