Differences in the QBO response to stratospheric aerosol modification depending on injection strategy and species

A known adverse side effect of stratospheric aerosol modification (SAM) is the modification of the quasi-biennial oscillation (QBO), which is caused by the stratospheric heating associated with an artificial aerosol layer. Multiple studies found the QBO to slow down or even completely vanish for point-like injections of SO2 at the equator. The cause for this was found to be a modification of the thermal wind balance and a stronger tropical upwelling. For other injection strategies, different responses of the QBO have been observed. It has not yet been presented a theory which is able to explain those differences in a comprehensive manner, which is further complicated by the fact that the simulated QBO response is highly sensitive to the used model even under identical boundary conditions. Therefore, within this study we investigate the response of the QBO to SAM for three different injection strategies (point-like injection at the equator, point-like injection at 30° N and 30° S simultaneously, and areal injection into a 60° wide belt along the equator). Our simulations confirm that the QBO response significantly depends on the injection location. Based on the thermal wind balance, we demonstrate that this dependency is explained by differences in the meridional structure of the aerosol-induced stratospheric warming, i.e. the location and meridional extension of the maximum warming. Additionally, we also tested two different injection species (SO2 and H2SO4). The QBO response is qualitatively similar for both investigated injection species. Comparing the results to corresponding results of a second model, we further demonstrate the generality of our theory as well as the importance of an interactive treatment of stratospheric ozone for the simulated QBO response

Singular del Pezzo surfaces that are equivariant compactifications

We determine which singular del Pezzo surfaces are equivariant compactifications of G_a^2, to assist with proofs of Manin's conjecture for such surfaces. Additionally, we give an example of a singular quartic del Pezzo surface that is an equivariant compactification of a semidirect product of G_a and G_m.Comment: 14 pages, main result extended to non-closed ground field

Collider signals from slow decays in supersymmetric models with an intermediate-scale solution to the mu problem

The problem of the origin of the mu parameter in the Minimal Supersymmetric Standard Model can be solved by introducing singlet supermultiplets with non-renormalizable couplings to the ordinary Higgs supermultiplets. The Peccei-Quinn symmetry is broken at a scale which is the geometric mean between the weak scale and the Planck scale, yielding a mu term of the right order of magnitude and an invisible axion. These models also predict one or more singlet fermions which have electroweak-scale masses and suppressed couplings to MSSM states. I consider the case that such a singlet fermion, containing the axino as an admixture, is the lightest supersymmetric particle. I work out the relevant couplings in several of the simplest models of this type, and compute the partial decay widths of the next-to-lightest supersymmetric particle involving leptons or jets. Although these decays will have an average proper decay length which is most likely much larger than a typical collider detector, they can occasionally occur within the detector, providing a striking signal. With a large sample of supersymmetric events, there will be an opportunity to observe these decays, and so gain direct information about physics at very high energy scales.Comment: 24 pages, LaTeX, 4 figure

Possibility of spontaneous CP violation in the nonminimal supersymmetric standard model with two neutral Higgs singlets

A supersymmetric standard model with two Higgs doublets and two Higgs singlets is investigated if it can accommodate the possibility of spontaneous CP violation. Assuming the degeneracy of the scalar quark masses of the third generation, we find that spontaneous CP violation in the Higgs sector is viable in our model. In the case of spontaneous CP violation, the masses of the lightest two neutral Higgs bosons are estimated to be 80 and 125 GeV for some parameter values in our model, which, are consistent with LEP2 data.Comment: 18 pages, 3figure

Real-space anisotropy of the superconducting gap in the charge-density wave material 2H-NbSe2

We present a scanning tunneling microscopy (STM) and ab-initio study of the anisotropic superconductivity of 2H-NbSe2 in the charge-density-wave (CDW) phase. Differential-conductance spectra show a clear double-peak structure, which is well reproduced by density functional theory simulations enabling full k- and real-space resolution of the superconducting gap. The hollow-centered (HC) and chalcogen-centered (CC) CDW patterns observed in the experiment are mapped onto separate van der Waals layers with different electronic properties. We identify the CC layer as the high-gap region responsible for the main STM peak. Remarkably, this region belongs to the same Fermi surface sheet that is broken by the CDW gap opening. Simulations reveal a highly anisotropic distribution of the superconducting gap within single Fermi sheets, setting aside the proposed scenario of a two-gap superconductivity. Our results point to a spatially localized competition between superconductivity and CDW involving the HC regions of the crystal

An interactive stratospheric aerosol model intercomparison of solar geoengineering by stratospheric injection of SO2 or accumulation-mode sulfuric acid aerosols

Studies of stratospheric solar geoengineering have tended to focus on modification of the sulfuric acid aerosol layer, and almost all climate model experiments that mechanistically increase the sulfuric acid aerosol burden assume injection of SO2. A key finding from these model studies is that the radiative forcing would increase sublinearly with increasing SO2 injection because most of the added sulfur increases the mass of existing particles, resulting in shorter aerosol residence times and aerosols that are above the optimal size for scattering. Injection of SO3 or H2SO4 from an aircraft in stratospheric flight is expected to produce particles predominantly in the accumulation-mode size range following microphysical processing within an expanding plume, and such injection may result in a smaller average stratospheric particle size, allowing a given injection of sulfur to produce more radiative forcing. We report the first multi-model intercomparison to evaluate this approach, which we label AM-H2SO4 injection. A coordinated multi-model experiment designed to represent this SO3- or H2SO4-driven geoengineering scenario was carried out with three interactive stratospheric aerosol microphysics models: the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM2) with the Whole Atmosphere Community Climate Model (WACCM) atmospheric configuration, the Max-Planck Institute's middle atmosphere version of ECHAM5 with the HAM microphysical module (MAECHAM5-HAM) and ETH's SOlar Climate Ozone Links with AER microphysics (SOCOL-AER) coordinated as a test-bed experiment within the Geoengineering Model Intercomparison Project (GeoMIP). The intercomparison explores how the injection of new accumulation-mode particles changes the large-scale particle size distribution and thus the overall radiative and dynamical response to stratospheric sulfur injection. Each model used the same injection scenarios testing AM-H2SO4 and SO2 injections at 5 and 25 Tg(S) yr-1 to test linearity and climate response sensitivity. All three models find that AM-H2SO4 injection increases the radiative efficacy, defined as the radiative forcing per unit of sulfur injected, relative to SO2 injection. Increased radiative efficacy means that when compared to the use of SO2 to produce the same radiative forcing, AM-H2SO4 emissions would reduce side effects of sulfuric acid aerosol geoengineering that are proportional to mass burden. The model studies were carried out with two different idealized geographical distributions of injection mass representing deployment scenarios with different objectives, one designed to force mainly the midlatitudes by injecting into two grid points at 30° N and 30° S, and the other designed to maximize aerosol residence time by injecting uniformly in the region between 30° S and 30° N. Analysis of aerosol size distributions in the perturbed stratosphere of the models shows that particle sizes evolve differently in response to concentrated versus dispersed injections depending on the form of the injected sulfur (SO2 gas or AM-H2SO4 particulate) and suggests that prior model results for concentrated injection of SO2 may be strongly dependent on model resolution. Differences among models arise from differences in aerosol formulation and differences in model dynamics, factors whose interplay cannot be easily untangled by this intercomparison. Copyright © 2022 Debra K. Weisenstein et al

Difficult Scenarios for NMSSM Higgs Discovery at the LHC

We identify scenarios not ruled out by LEP data in which NMSSM Higgs detection at the LHC will be particularly challenging. We first review the `no-lose' theorem for Higgs discovery at the LHC that applies if Higgs bosons do not decay to other Higgs bosons - namely, with L=300 fb^-1, there is always one or more `standard' Higgs detection channel with at least a 5 sigma signal. However, we provide examples of no-Higgs-to-Higgs cases for which all the standard signals are no larger than 7 sigma implying that if the available L is smaller or the simulations performed by ATLAS and CMS turn out to be overly optimistic, all standard Higgs signals could fall below 5 sigma even in the no-Higgs-to-Higgs part of NMSSM parameter space. In the vast bulk of NMSSM parameter space, there will be Higgs-to-Higgs decays. We show that when such decays are present it is possible for all the standard detection channels to have very small significance. In most such cases, the only strongly produced Higgs boson is one with fairly SM-like couplings that decays to two lighter Higgs bosons (either a pair of the lightest CP-even Higgs bosons, or, in the largest part of parameter space, a pair of the lightest CP-odd Higgs bosons). A number of representative bench-mark scenarios of this type are delineated in detail and implications for Higgs discovery at various colliders are discussed.Comment: 31 pages, 5 figure

Structure, dielectric relaxation and electrical conductivity of 2,3,7,8-Tetramethoxychalcogenanthrene-2,3-dichloro-5,6-dicyano-1,4-benzoquinone 1:1 charger-transfer complexes

[EN] 2,3,7,8-Tetramethoxychalcogenanthrenes (5,10-chalcogena-cyclo-diveratrylenes, 'Vn(2)E(2)', E = S, Se) form isotypical 1:1 charge-transfer (CT) complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). X-ray analysis of Vn(2)S(2) . DDQ shows the compound to have a columnar structure with segregated stacks of donors and acceptors. The donors are virtually planar in accordance with a formulation of [Vn(2)E(2)](+)[DDQ](-). Donor cations and acceptor anions are equidistant in their respective stacks, but in each case they inclined to the stacking axis, nevertheless guaranteeing an optimum overlap of the half-filled frontier orbitals which are of pi-type character according to MNDO calculations. Dielectric ac measurements of permittivity epsilon' and loss factor E '' clearly reveal two processes, a dielectric one at low temperatures and a conductive one at high temperatures. The dielectric process can be described by the Havriliak-Negami (HN) and the Kohlrausch-Williams-Watts (KWW) model, and the conductive process by a Debye-type plot. Using these methods, the relevant parameters are evaluated. The de conductivities of polycrystalline samples moulded at 10(8) Pa show a temperature dependence in the plots of ln sigma vs. T-1, which is typical of semiconductors. Two slopes are found; that in the low-temperature region (<285 K) is explained by an easy-path model (intragrain conductivity with low activation energies), whereas in the high-temperature region conduction across the grain boundaries (with higher activation energies) is becoming predominant. The activation energies for the intrinsic conductivities obtained by the ac and de measurements are similar. Despite the columnar structure with segregated stacks, due to stoichiometric oxidation states of the components, the absolute values of conductivity are low ten. 10(-6) S cm(-1) at 293 K), though higher (by a factor of ca. 10(3)) than those of compounds like Vn(2)E(2) . TCNQ with stacks in which donor and acceptor molecules alternate.Behrens, U.; Díaz Calleja, R.; Dötze, M.; Franke, U.; Gunsser, W.; Klar, G.; Kudnig, J.... (1996). Structure, dielectric relaxation and electrical conductivity of 2,3,7,8-Tetramethoxychalcogenanthrene-2,3-dichloro-5,6-dicyano-1,4-benzoquinone 1:1 charger-transfer complexes. Journal of Materials Chemistry. 6(4):547-553. https://doi.org/10.1039/JM9960600547S54755364Behrens, J., Hinrichs, W., Link, T., Schiffling, C., & Klar, G. (1995). SELFSTACKING SYSTEMS, PART 6.1HOST LATTICE FUNCTION OF 2,3,8,9-TETRAMETHOXYDIBENZO[c,e][1,2]-DICHALCOGENINS IN THEIR ELECTRICALLY CONDUCTING IODINE COMPLEXES. Phosphorus, Sulfur, and Silicon and the Related Elements, 101(1-4), 235-244. doi:10.1080/10426509508042522Berges, P., Kudnig, J., Klar, G., Martínez, E. S., & Calleja, R. D. (1989). Elementorganische Verbindungen mit o-Phenylenresten, XVI . 2:1-Komplexe von 2,3,7,8-Tetramethoxychalcogenanthrenen mit Tetracyanethen / Organometallic Compounds with o-Phenylene Substituents, Part XVI 2:1-Complexes of 2,3,7,8-Tetramethoxychalcogenanthrenes with Tetracyanoethene. Zeitschrift für Naturforschung B, 44(2), 211-219. doi:10.1515/znb-1989-0219Hinrichs, W., Berges, P., Klar, G., Sánchez-Martínez, E., & Gunsser, W. (1987). Structure and electrical conductivity of TCNQ-2,3,7,8-tetramethoxychalcogenanthrene complexes. Synthetic Metals, 20(3), 357-364. doi:10.1016/0379-6779(87)90832-0Sánchez Martínez, E., Díaz Calleja, R., Gunsser, W., Berges, P., & Klar, G. (1989). Structure and dielectric relaxation of 2,3,7,8-tetramethoxychalcogenanthrene-TCNQ complexes. Synthetic Metals, 30(1), 67-78. doi:10.1016/0379-6779(89)90642-5Gunßer, W., Henning, J. H., Klar, G., & Martínez, E. S. (1989). Spin Density and Magnetic Susceptibility of Charge-Transfer Complexes with Chalkogenanthrene Donors. Berichte der Bunsengesellschaft für physikalische Chemie, 93(11), 1370-1373. doi:10.1002/bbpc.19890931148G. M. Sheldrick , SHELXTL-PLUS, Release 4.21/0, Siemens Analytical X-Ray Instruments, 1990.Bock, H., Rauschenbach, A., Näther, C., Havlas, Z., Gavezzotti, A., & Filippini, G. (1995). Orthorhombisches und monoklines 2,3,7,8-Tetramethoxythianthren: kleiner Strukturunterschied – große Gitteränderung. Angewandte Chemie, 107(1), 120-122. doi:10.1002/ange.19951070132Bock, H., Rauschenbach, A., Näther, C., Havlas, Z., Gavezzotti, A., & Filippini, G. (1995). Orthorhombic and Monoclinic 2,3,7,8-Tetramethoxythianthrene: Small Structural Difference–Large Lattice Change. Angewandte Chemie International Edition in English, 34(1), 76-78. doi:10.1002/anie.199500761Hinrichs, W., Berges, P., & Klar, G. (1987). Selbststapelnde Systeme, IV 2,3,7,8-Tetramethoxythianthreniumsalze/Selfstacking Systems, Part IV 2.3.7.8-Tetramethoxythianthrenium Salts. Zeitschrift für Naturforschung B, 42(2), 169-176. doi:10.1515/znb-1987-0209Peover, M. E. (1962). 879. A polarographic investigation into the redox behaviour of quinones: the roles of electron affinity and solvent. Journal of the Chemical Society (Resumed), 4540. doi:10.1039/jr9620004540Wheland, R. C., & Gillson, J. L. (1976). Synthesis of electrically conductive organic solids. Journal of the American Chemical Society, 98(13), 3916-3925. doi:10.1021/ja00429a030Zanotti, G., Del Pra, A., & Bozio, R. (1982). Structure of tetraethylammonium–2,3-dichloro-5,6-dicyano-p-benzoquinone. Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 38(4), 1225-1229. doi:10.1107/s0567740882005330Zanotti, G., Bardi, R., & Del Pra, A. (1980). Structure of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 36(1), 168-171. doi:10.1107/s0567740880002750Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Cleveland, OH, 1977–1978, 58th edn., p. D–178.Sánchez Martínez, E., Díaz Calleja, R., Berges, P., Kudnig, J., & Klar, G. (1989). Structure, electrical conductivity and dielectric relaxation of a 1,2-dimethoxybenzene-tetracyanoethene 1:1 complex. Synthetic Metals, 32(1), 79-89. doi:10.1016/0379-6779(89)90831-xÅsbrink, L., Fridh, C., & Lindholm, E. (1977). HAM/3, a semi-empirical MO theory. I. The SCF method. Chemical Physics Letters, 52(1), 63-68. doi:10.1016/0009-2614(77)85121-xÅsbrink, L., Fridh, C., & Lindholm, E. (1977). HAM/3, a semi-empirical MO theory. III. Unoccupied orbitals. Chemical Physics Letters, 52(1), 72-75. doi:10.1016/0009-2614(77)85123-3Dewar, M. J. S., & Thiel, W. (1977). Ground states of molecules. 38. The MNDO method. Approximations and parameters. Journal of the American Chemical Society, 99(15), 4899-4907. doi:10.1021/ja00457a004Dewar, M. J. S., & Thiel, W. (1977). Ground states of molecules. 39. MNDO results for molecules containing hydrogen, carbon, nitrogen, and oxygen. Journal of the American Chemical Society, 99(15), 4907-4917. doi:10.1021/ja00457a005Åsbrink, L., Fridh, C., & Lindholm, E. (1978). Valence excitation of linear molecules.I. Excitation and UV spectra of N2, Co, acetylene and HCN. Chemical Physics, 27(2), 159-168. doi:10.1016/0301-0104(78)88001-xFridh, C., Åsbrink, L., & Lindholm, E. (1978). Valence excitation of linear molecules. II. Excitation and UV spectra of C2N2, CO2 and N2O. Chemical Physics, 27(2), 169-181. doi:10.1016/0301-0104(78)88002-1Lindholm, E., Bieri, G., Åsbrink, L., & Fridh, C. (1978). 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Production and Decay of Neutralinos in the Next-To-Minimal Supersymmetric Standard Model

Within the framework of the Next-To-Minimal Supersymmetric Standard Model (NMSSM) we study neutralino production $e^+e^- \longrightarrow \tilde{\chi}^0_i \tilde{\chi}^0_j$ ($i,j=1,\ldots ,5$) at center-of-mass energies between 100 and 600 GeV and the decays of the heavier neutralinos into the LSP plus a fermion pair, a photon or a Higgs boson. For representative gaugino/higgsino mixing scenarios, where the light neutralinos have significant singlet components, we find some striking differences between the NMSSM and the minimal supersymmetric model. Since in the NMSSM neutralino and Higgs sector are strongly correlated, the decay of the second lightest neutralino into a Higgs boson and the LSP often is kinematically possible and even dominant in a large parameter region of typical NMSSM scenarios. Also, the decay rates into final states with a photon may be enhanced.Comment: 36 pages, latex, 10 uuendcoded figures, complete ps file available at ftp://ftp.physik.uni-wuerzburg.de/pub/preprint/WUE-ITP-95-021.ps.g