Spinorial cohomology and maximally supersymmetric theories

Fields in supersymmetric gauge theories may be seen as elements in a spinorial cohomology. We elaborate on this subject, specialising to maximally supersymmetric theories, where the superspace Bianchi identities, after suitable conventional constraints are imposed, put the theories on shell. In these cases, the spinorial cohomologies describe in a unified manner gauge transformations, fields and possible deformations of the models, e.g. string-related corrections in an alpha' expansion. Explicit cohomologies are calculated for super-Yang-Mills theory in D=10, for the N=(2,0) tensor multiplet in D=6 and for supergravity in D=11, in the latter case from the point of view of both the super-vielbein and the super-3-form potential. The techniques may shed light on some questions concerning the alpha'-corrected effective theories, and result in better understanding of the role of the 3-form in D=11 supergravity.Comment: 23 pp, plain tex. v2: Minor changes, references adde

Manifestly supersymmetric M-theory

In this paper, the low-energy effective dynamics of M-theory, eleven-dimensional supergravity, is taken off-shell in a manifestly supersymmetric formulation. We show that a previously proposed relaxation of the superspace torsion constraints does indeed accommodate a current supermultiplet which lifts the equations of motion corresponding to the ordinary second order derivative supergravity lagrangian. Whether the auxiliary fields obtained this way can be used to construct an off-shell lagrangian is not yet known. We comment on the relation and application of this completely general formalism to higher-derivative (R^4) corrections. Some details of the calculation are saved for a later publication.Comment: 13 pages, plain tex. v2: minor changes, one ref. adde

Chiral surfaces self-assembling in one-component systems with isotropic interactions

We show that chiral symmetry can be broken spontaneously in one-component systems with isotropic interactions, i.e. many-particle systems having maximal a priori symmetry. This is achieved by designing isotropic potentials that lead to self-assembly of chiral surfaces. We demonstrate the principle on a simple chiral lattice and on a more complex lattice with chiral super-cells. In addition we show that the complex lattice has interesting melting behavior with multiple morphologically distinct phases that we argue can be qualitatively predicted from the design of the interaction.Comment: 4 pages, 4 figure

Timelike self-similar spherically symmetric perfect-fluid models

Einstein's field equations for timelike self-similar spherically symmetric perfect-fluid models are investigated. The field equations are rewritten as a first-order system of autonomous differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system is reduced as far as possible and so that the reduced phase space becomes compact and regular. The system is subsequently analysed qualitatively using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure

X-ray fluorescence spectra of metals excited below threshold

X-ray scattering spectra of Cu and Ni metals have been measured using monochromatic synchrotron radiation tuned from far above to more than 10 eV below threshold. Energy conservation in the scattering process is found to be sufficient to explain the modulation of the spectral shape, neglecting momentum conservation and channel interference. At excitation energies close to and above threshold, the emission spectra map the occupied local partial density of states. For the sub-threshold excitations, the high-energy flank of the inelastic scattering exhibits a Raman-type linear dispersion, and an asymmetric low energy tail develops. For excitation far below threshold the emission spectra are proportional to a convolution of the occupied and unoccuppied local partial densities of states.Comment: 10 pages, 3 figures, http://link.aps.org/doi/10.1103/PhysRevB.68.04511

Aerosol formation over the Boreal forest in Hyytiälä, Finland: monthly frequency and annual cycles ? the roles of air mass characteristics and synoptic scale meteorology

International audienceNew atmospheric particles with diameters of 3?10 nm and their subsequent growth to cloud condensation nucleus have been observed at various places in the European boundary layer. These events have been observed simultaneously within wide geographical areas (over 1000 km) in connection to specific weather systems, the cold air behind cyclones. Here we show that atmospheric aerosol formation (i.e. nucleation and initial growth) is favoured by the outbreak of cold Arctic air over northern Europe. Aerosol formation was about twice as common in Arctic air as in sub-Polar air, and even more so compared to other air masses. The most important general factor favouring aerosol formation in Arctic air and marine air was weaker competing condensational sink (CS) for the precursor gases (less pre-existing aerosols), while high CS prevented aerosol formation in heated sub-Polar air and mid-latitude air. High SO2 levels favoured nucleation in continental air and high UV-B radiation in sub-tropical air. The critical factor that determined if aerosol formation would start on a day with Arctic air was the UV-B radiation. The same applied to sub-Polar air and continental air, while increased SO2 concentration could trigger formation in heated sub-Polar and mid-latitude air, and reduced CS could cause formation in mid-latitude, marine or mixed/transient air. We speculate that strong emissions of volatile organic compounds from the Boreal forest and strong boundary layer dynamics may have caused aerosol formation in sub-Polar air masses and air in transition from a marine to a continental character. The monthly frequency of Arctic air masses and the probability for photo-chemically driven aerosol formation explains the observed annual cycle in monthly particle formation frequency as well as much of the inter annual variability. The same cyclones that transport cold, clean air from the Arctic to Europe will also transport warm polluted air in the other direction, which help cause the Arctic Haze phenomena. The cyclones have a key role for the atmospheric aerosol life cycle in mid to high latitudes. Due to the observed growth to the size of CCN in one to two days, there is a potential feed back from the effects on the CCN population and cloud albedo even within the same weather system, but also on the climatic time scale

Kinetic modelling of runaway electron avalanches in tokamak plasmas

Runaway electrons (REs) can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force due to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate REs mainly through knock-on collisions, where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of REs. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3-D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. A bounce-averaged knock-on source term is derived. The generation of REs from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3-D linearized bounce-averaged relativistic electron Fokker-Planck equation, through the calculation of the response of the electron distribution function to a constant parallel electric field. This work shows that the avalanche effect can be important even in non-disruptive scenarios. RE formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons cannot contribute to the RE population. The relative importance of the avalanche mechanism is investigated as a function of the key parameters for RE formation; the plasma temperature and the electric field strength. In agreement with theoretical predictions, the simulations show that in low temperature and E-field knock-on collisions are the dominant source of REs and can play a significant role for RE generation, including in non-disruptive scenarios.Comment: 23 pages, 12 figure

Cap Management for LULUCF Options: An economic mechanism design to preserve the environmental and social integrity of forest related LULUCF activities under the Kyoto Protocol

In this paper we identify four main problems that arise from a quantitative cap on land use, land-use change and forestry activities discussed at OP 6. These problems relate to environmental integrity and economic efficiency. First, in stark contrast to the wording of the United Nations Framework Convention for Climate Change and the Kyoto Protocol the proposed provisions for land use, land use change and forestry activities are only about carbon accounting and are devoid of sustainability criteria. This deficiency would make climate actions inconsistent with other international agreements and policy processes. Second, due to lower costs of sequestration activities a quantitative cap produces possibilities for arbitrage in the greenhouse gas market. Third, in a situation of oversupply a fair allocation of highly profitable sequestration projects is unlikely. Fourth, negotiators are overwhelmed by the complexity of the land use, land-use change and forestry issue. The currently proposed mechanisms, such as adaptation levies or discounted crediting of flexibilities, do not provide adequate solutions. In order to solve these problems we propose a tender auction mechanism that could already be applied today for forest sinks. We distinguish between two information components in this economic mechanism. First, a qualifier component in the form of certification for sustainable forest management practices, which is already in use by market actors worldwide. Second, a competitive trait in the form of carbon sequestration intensities per greenhouse gas emission credit. Under such a regime, negotiators simply need to determine a quantitative cap (as they already started to negotiate at COP 6), while an efficient market mechanism guarantees integrity with respect to sustainability and economic efficiency criteria. The complexity of the issues surrounding land use, land use change and forestry activities is transferred to a decentralized decision making process. The proposed mechanism can also serve as a template for clean development mechanism projects and other international flexible mechanisms or subsidy programs