Off-shell N=(4,4) supersymmetry for new (2,2) vector multiplets

We discuss the conditions for extra supersymmetry of the N=(2,2) supersymmetric vector multiplets described in arXiv:0705.3201 [hep-th] and in arXiv:0808.1535 [hep-th]. We find (4,4) supersymmetry for the semichiral vector multiplet but not for the Large Vector Multiplet.Comment: 15 page

Sigma models with off-shell N=(4,4) supersymmetry and noncommuting complex structures

We describe the conditions for extra supersymmetry in N=(2,2) supersymmetric nonlinear sigma models written in terms of semichiral superfields. We find that some of these models have additional off-shell supersymmetry. The (4,4) supersymmetry introduces geometrical structures on the target-space which are conveniently described in terms of Yano f-structures and Magri-Morosi concomitants. On-shell, we relate the new structures to the known bi-hypercomplex structures.Comment: 20 pages; v2: significant corrections, clarifications, and reorganization; v3: discussion of supersymmetry vs twisted supersymmetry added, relevant signs corrected

The clumped-isotope geochemistry of exhumed marbles from Naxos, Greece

Exhumation and accompanying retrograde metamorphism alter the compositions and textures of metamorphic rocks through deformation, mineral–mineral reactions, water–rock reactions, and diffusion-controlled intra- and inter-mineral atomic mobility. Here, we demonstrate that these processes are recorded in the clumped- and single-isotope (δ^(13)C and δ^(18)O) compositions of marbles, which can be used to constrain retrograde metamorphic histories. We collected 27 calcite and dolomite marbles along a transect from the rim to the center of the metamorphic core-complex of Naxos (Greece), and analyzed their carbonate single- and clumped-isotope compositions. The majority of Δ_(47) values of whole-rock samples are consistent with exhumation- controlled cooling of the metamorphic complex. However, the data also reveal that water–rock interaction, deformation driven recrystallization and thermal shock associated with hydrothermal alteration may considerably impact the overall distribution of Δ_(47) values. We analyzed specific carbonate fabrics influenced by deformation and fluid–rock reaction to study how these processes register in the carbonate clumped-isotope system. Δ_(47) values of domains drilled from a calcite marble show a bimodal distribution. Low Δ_(47_ values correspond to an apparent temperature of 260 °C and are common in static fabrics; high Δ_(47) values correspond to an apparent temperature of 200 °C and are common in dynamically recrystallized fabrics. We suggest that the low Δ_(47) values reflect diffusion-controlled isotopic reordering during cooling, whereas high Δ_(47) values reflect isotopic reordering driven by dynamic recrystallization. We further studied the mechanism by which dynamic recrystallization may alter Δ_(47) values by controlled heating experiments. Results show no significant difference between laboratory reactions rates in the static and dynamic fabrics, consistent with a mineral-extrinsic mechanism, in which slip along crystal planes was associated with atomic-scale isotopic reordering in the calcite lattice. An intrinsic mechanism (enhanced isotopic reordering rate in deformed minerals) is contraindicated by these experiments. We suggest that Δ_(47) values of dynamically recrystallized fabrics that form below the diffusion-controlled blocking-temperature for calcite constrain the temperature of deformation. We find that Δ_(47)-based temperatures of static fabrics from Naxos marbles are ∼60–80 °C higher than commonly observed in slowly cooled metamorphic rocks, and would suggest cooling rates of ∼10^5°C Myr^(−1). A similar thermal history is inferred for dolomite marbles from the core vicinity, which preserve apparent temperatures up to 200 °C higher than a typical blocking temperature (∼300 °C). This finding could be explained by a hydrothermal event driving a brief thermal pulse and locally resetting Δ_(47) values. Rapid cooling of the core-complex region is consistent with a compilation of published cooling ages and a new apatite U–Th/He age, associating the thermal event with the emplacement of a granodiorite pluton at ∼12 Ma

T-duality and Generalized Kahler Geometry

We use newly discovered N = (2, 2) vector multiplets to clarify T-dualities for generalized Kahler geometries. Following the usual procedure, we gauge isometries of nonlinear sigma-models and introduce Lagrange multipliers that constrain the field-strengths of the gauge fields to vanish. Integrating out the Lagrange multipliers leads to the original action, whereas integrating out the vector multiplets gives the dual action. The description is given both in N = (2, 2) and N = (1, 1) superspace.Comment: 14 pages; published version: some conventions improved, minor clarification

Sources, Timing, Environmental and Tectonic Implications of Epigenetic Mineralization Along the Arabian‐African Plate Boundary

Abstract The formation of divergent plate boundaries involves the opening of continental basins and uplift of plate margins accompanied by seawater ingression and the reorganization of surface and groundwater drainage systems. These processes drive water‐rock reactions, resulting in the deposition of epigenetic minerals in the country rock adjacent to the plate boundary. Here, we study the isotopic geochemical record of epigenetic dolomite and ferric‐oxide minerals that occur along tectonic lines in the Negev (southern Israel), which border the Cenozoic rift system that developed between the African and Arabian plates. The observed ranges of new and published O, C, Sr, Mo, Fe, and Pb isotope compositions indicate mixing between the country rock, seawater and deep‐seated groundwater source‐solutions. We suggest that mineralization occurred as brines migrated from their marine source, mixed with groundwater in a deep siliciclastic aquifer environment, and subsequently upwelled along tectonic lines and reacted with the overlying carbonate rocks. Relative and U‐Pb dating of epigenetic minerals suggest that mineralization occurred at 31.4 ± 4.6 Ma in the central Negev sites and at 46 ± 12 Ma and again at 14.5 ± 2.3 Ma in the northeast Negev. The younger two ages overlap the timing of pre‐ Red Sea Rift doming of northeastern Africa and Arabia, driven by the Afar Plume, and lateral‐movement along the Dead Sea Transform (DST), respectively. We associate the youngest mineralization event with a time‐interval in which the DST already hosted a marine lagoon, while the transform's western margin has remained a low relief landscape

Styles and rates of long-term denudation in carbonate terrains under a Mediterranean to hyper-arid climatic gradient

Carbonate minerals, unlike silicates, have the potential to dissolve almost completely and with high efficiency. Thus, in carbonate terrains denudation rate and style (the governing process of denudation, mechanical or chemical) should be more sensitive to climatic forcing. Using 36Cl measurements in 39 carbonate bedrock and sediment samples, we calculate long-term denudation rates across a sharp climatic gradient from Mediterranean to hyper-arid conditions. Our samples were collected along the Arugot watershed, which drains the eastern flank of the Judea Range (central Israel) to the Dead Sea and is characterized by a pronounced rain shadow. Denudation rates of flat-lying bedrock outcrops sampled along interfluves differ by an order of magnitude from ∼20 mm ka−1 in the Mediterranean zone to 1–3 mm ka−1 in the hyper-arid zone. These rates are strongly correlated with precipitation, and thus reflect the importance of carbonate mineral dissolution in the overall denudation process. In contrast, denudation rates of steep bedrock surfaces depend on the hillslope gradient, but in the hyper-arid climate zone, indicating that mechanical processes dominate the overall hillslope denudation within this zone. The dominance of slope-dependent mechanical erosion in the hyper-arid zone is also reflected by an increase in spatially-average denudation rates from 17–19 mm ka−1 in the Mediterranean–semi-arid zones to 21–25 mm ka−1 in the hyper-arid zone. These higher rates are attributed to clast contribution from steep slopes under arid climate. This suggests an increased importance of mechanical processes to the overall denudation in the hyper-arid zone. We demonstrate that the transition between chemically-dominated denudation to mechanically-dominated denudation occurs between 100 and 200 mm of mean annual precipitation. Long-term denudation rates across the Judea Range indicate that between Mediterranean and hyper-arid climates, chemical weathering rates are limited by precipitation. Nevertheless, in more humid climates, ch