1,220 research outputs found

    Grassland carbon sequestration and emissions following cultivation in a mixed crop rotation

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    Grasslands are potential carbon sinks to reduce unprecedented increase in atmospheric CO2. Effect of age (1 to 4-yr-old) and management (slurry, grazing multispecies mixture) of a grass phase mixed crop rotation on carbon sequestration and emissions upon cultivation was compared with 17-yr-old grassland and a pea field as reference. Aboveground and root biomass were determined and soils were incubated to study CO2 emissions after soil disturbance. Aboveground biomass was highest in 1-yr-old grassland with slurry application and lowest in 4-yr-old grassland without slurry application. Root biomass was highest in 4-yr-old grassland, but all 1 to 4-yr-old grasslands were in between the pea field (0.81±0.094 g kg-1 soil) and the 17-yr-old grassland (3.17±0.22 g kg-1 soil). Grazed grasslands had significantly higher root biomass than cut grasslands. There was no significant difference in the CO2 emissions within 1 to 4-yr-old grasslands. Only the 17-yr-old grassland showed markedly higher CO2 emissions (4.9 ± 1.1 g CO2 kg-1 soil). Differences in aboveground and root biomass did not affect CO2 emissions, and slurry application did not either. The substantial increase in root biomass with age but indifference in CO2 emissions across the age and management in temporary grasslands, thus, indicates potential for long-term sequestration of soil C

    Type IIA Orientifold Limit of M-Theory on Compact Joyce 8-Manifold of Spin(7)-Holonomy

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    We show that M-theory compactified on a compact Joyce 8-manifold of Spin(7)Spin(7)-holonomy, which yields an effective theory in D=3D = 3 with N\N = 1 supersymmetry, admits at some special points in it moduli space a description in terms of type IIA theory on an orientifold of compact Joyce 7-manifold of G2G_2-holonomy. We find the evidence in favour of this duality by computing the massless spectra on both M-thory side and type IIA side. For the latter, we compute the massless spectra by going to the orbifold limit of the Joyce 7-manifold.Comment: 26 pages, 2 eps figures, Latex file, two references and one footnote added, corrected some typo

    Sitting on the Domain Walls of N=1 Super Yang-Mills

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    In pure N=1 supersymmetric Yang-Mills with gauge group SU(N), the domain walls which separate the N vacua have been argued, on the basis of string theory realizations, to be D-branes for the confining string. In a certain limit, this means that a configuration of k parallel domain walls is described by a 2+1-dimensional U(k) gauge theory. This theory has been identified by Acharya and Vafa as the U(k) gauge theory with 4 supercharges broken by a Chern-Simons term of level N in such a way that 2 supercharges are preserved. We argue further that the gauge coupling of the domain wall gauge theory goes like g^2 ~ Lambda/N, for large N. In the case of two domain walls, we show that the U(2) world-volume theory generates a quadratic potential on the Coulomb branch at two loops in perturbation theory which is consistent with there being a supersymmetric bound state of the two wall system. A mass gap of order Lambda/N is generated around the supersymmetric minimum and we estimate the size of the bound-state to be order Lambda/ \sqrt N. At large distance the potential reaches a constant that can qualitatively account for the binding energy of the two walls even though stringy effects are not, strictly speaking, decoupled.Comment: 18 pages, LaTex. 6 figure

    The Baryon-Dark Matter Ratio Via Moduli Decay After Affleck-Dine Baryogenesis

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    Low-scale supersymmetry breaking in string motivated theories implies the presence of O(100) TeV scale moduli, which generically lead to a significant modification of the history of the universe prior to Big Bang Nucleosynthesis. Such an approach implies a non-thermal origin for dark matter resulting from scalar decay, where the lightest supersymmetric particle can account for the observed dark matter relic density. We study the further effect of the decay on the baryon asymmetry of the universe, and find that this can satisfactorily address the problem of the over-production of the baryon asymmetry by the Affleck-Dine mechanism in the MSSM. Remarkably, there is a natural connection between the baryon and dark matter abundances today, which leads to a solution of the `Cosmic Coincidence Problem'.Comment: 12 pages, no figure. v2: references adde

    On Mirror Symmetry for Manifolds of Exceptional Holonomy

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    We consider Type II string theories on Tn/Z2m{\bf T^n}/{{\bf Z_2}^m} Joyce orbifolds. This class contains orbifolds which can be desingularised to give manifolds of G2G_2 (n({\bf n}==7)7) and Spin(7)Spin(7) holonomy (n({\bf n}==8)8). In the G2G_2 holonomy case we present two types of TT-duality transformation which are clearly generalisations of the TT-duality/mirror transformation in Calabi-Yau spaces. The first maps Type IIA theory on one such space from this class to Type IIB theory on another such space. The second maps Type IIA (IIB) to Type IIA (IIB). In the case of Spin(7)Spin(7) holonomy we present a TT-duality transformation which maps Type IIA (IIB) theory on one such space to Type IIA (IIB) on another such space. As orbifold conformal field theories these TT-dual target spaces are related via the inclusion/exclusion of discrete torsion and the TT-duality is proven to genus gg in string perturbation theory. We then apply a Strominger, Yau, Zaslow type argument which suggests that manifolds of G2G_2 holonomy which have a ``mirror'' of the first (second) type admit supersymmetric T3{\bf T^3} (T4{\bf T^4}) fibrations and that manifolds of Spin(7)Spin(7) holonomy for which a mirror exists admit fibration by supersymmetric 44-tori. Further evidence for this suggestion is given by examining the moduli space structure of wrapped D-branes.Comment: 20 Pages, Late

    Rotating membranes on G_2 manifolds, logarithmic anomalous dimensions and N=1 duality

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    We show that the ESlogSE-S \sim \log S behaviour found for long strings rotating on AdS5×S5AdS_5\times S^5 may be reproduced by membranes rotating on AdS4×S7AdS_4\times S^7 and on a warped AdS5AdS_5 M-theory solution. We go on to obtain rotating membrane configurations with the same EKlogKE-K \sim \log K relation on G2G_2 holonomy backgrounds that are dual to N=1{\mathcal{N}}=1 gauge theories in four dimensions. We study membrane configurations on G2G_2 holonomy backgrounds systematically, finding various other Energy-Charge relations. We end with some comments about strings rotating on warped backgrounds.Comment: 1+44 pages. Latex. No figures. Minor corrections to make all membrane configurations consistent. One configuration is now noncompac

    Features of deSitter Vacua in M-Theory

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    We compute the masses of all moduli in the unstable deSitter vacua arising in the toy model of cosmological M-theory flux compactifications on the G2 holonomy manifolds of [1]. The slow-roll parameters in the tachyonic directions are shown to be too large to be useful for conventional models of inflation. However, it appears that we can find fast roll regimes which could, under certain conditions, account for the current dark energy driven accelerated expansion of the universe.Comment: 14 pages, 1 figur

    Affleck-Dine baryogenesis in inflating curvaton scenario with O(1010210-10^2TeV) mass moduli curvaton

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    We study the Affleck-Dine (AD) baryogenesis in the inflating curvaton scenario, when the curvaton is a moduli field with O(1010210-10^2TeV) mass. A moduli field with such mass is known to be free from the Polonyi problem, and furthermore its decay products can explain the present cold dark matter abundance. In our scenario, it further explains the primordial curvature perturbation and the present baryon density all together. The current observational bound on the baryon isocurvature perturbation, which severely constrains the AD baryogenesis with the original oscillating moduli curvaton scenario, is shown to put practically negligible constraint if we replace the oscillating curvaton with the inflating curvaton.Comment: 1+21pages v2: minor correction v3: included short reviews, added refs, fixed typo

    Higher Dimensional Analogues of Donaldson-Witten Theory

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    We present a Donaldson-Witten type field theory in eight dimensions on manifolds with Spin(7)Spin(7) holonomy. We prove that the stress tensor is BRST exact for metric variations preserving the holonomy and we give the invariants for this class of variations. In six and seven dimensions we propose similar theories on Calabi-Yau threefolds and manifolds of G2G_2 holonomy respectively. We point out that these theories arise by considering supersymmetric Yang-Mills theory defined on such manifolds. The theories are invariant under metric variations preserving the holonomy structure without the need for twisting. This statement is a higher dimensional analogue of the fact that Donaldson-Witten field theory on hyper-K\"ahler 4-manifolds is topological without twisting. Higher dimensional analogues of Floer cohomology are briefly outlined. All of these theories arise naturally within the context of string theory.Comment: 23 Pages, Latex. Our statement that these theories are independent of the metric is corrected to the statement that the theories are invariant under deformations that preserve the holonomy structure of the manifold. We also include more details of the construction of a higher dimensional analogue of Floer theory. Three references are adde

    Scherk-Schwarz reduction of M-theory on G2-manifolds with fluxes

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    We analyse the 4-dimensional effective supergravity theories obtained from the Scherk--Schwarz reduction of M-theory on twisted 7-tori in the presence of 4-form fluxes. We implement the appropriate orbifold projection that preserves a G2-structure on the internal 7-manifold and truncates the effective field theory to an N=1, D=4 supergravity. We provide a detailed account of the effective supergravity with explicit expressions for the Kaehler potential and the superpotential in terms of the fluxes and of the geometrical data of the internal manifold. Subsequently, we explore the landscape of vacua of M-theory compactifications on twisted tori, where we emphasize the role of geometric fluxes and discuss the validity of the bottom-up approach. Finally, by reducing along isometries of the internal 7-manifold, we obtain superpotentials for the corresponding type IIA backgrounds.Comment: 43 pages, Latex; v3 typos corrected, one reference added, JHEP versio
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