2,166 research outputs found

    Wilson loops, geometric operators and fermions in 3d group field theory

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    Group field theories whose Feynman diagrams describe 3d gravity with a varying configuration of Wilson loop observables and 3d gravity with volume observables at each vertex are defined. The volume observables are created by the usual spin network grasping operators which require the introduction of vector fields on the group. We then use this to define group field theories that give a previously defined spin foam model for fermion fields coupled to gravity, and the simpler quenched approximation, by using tensor fields on the group. The group field theory naturally includes the sum over fermionic loops at each order of the perturbation theory.Comment: 13 pages, many figures, uses psfra

    Early Ceramics in Anatolia: Implications for the Production and Use of the Earliest Pottery. The Evidence from Boncuklu Höyük

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    Fragments of possible fired clay found at Boncuklu Höyük, central Turkey, appear to derive from rudimentary vessels, despite the later ninth- and early eighth-millennium cal. bc and thus ‘Aceramic’ dates for the site. This paper will examine the evidence for such fired clay vessels at Boncuklu and consider their implications as examples of some of the earliest pottery in Anatolia. The discussion will examine contextual evidence for the role of these fragments and consider their relative rarity at the site and the implications for the marked widespread adoption of pottery in southwest Asia c. 7000–6700 cal. bc

    Environmental Stress and Aroma Production During Wine Fermentation

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    The sensory description of wine uses the widest range of descriptive terminology of all food products, reflecting the complex nature of a product whose character depends on the balance of hundreds of individual flavour-active compounds. There are many tools that can influence flavour profiles or wine styles, one of which is the choice of a specific yeast strain. Yeasts contribute to wine flavour by producing volatile metabolites with different flavour profiles. The impact of changing environmental conditions on the production of flavour compounds by yeast strains remains largely unexplored. This is the first study investigating the impact of two mild fermentation stresses, hyperosmotic and temperature stress, on aroma production in synthetic must by commercial Saccharomyces cerevisiae wine strains. Hyperosmotic stress was imposed by cultivation of the yeast for 21 days in the must containing either 0.3 or 0.5 M sorbitol. The transient temperature stresses were applied for 16 h at 8° or 37°C for either two or eight days after commencement of the fermentation. Greater glycerol and acetic acid levels were produced by most yeasts when only hyperosmotic stress was applied. Hyperosmotic and temperature stress conditions produced a limited number of significant changes to the profile of the esters, higher alcohols and volatile fatty acids. These changes differed significantly for each strain and stress treatment, suggesting that the fermentation conditions can significantly alter the aromatic profile of a wine, although these stress impacts cannot be predicted in general. The changes to the aromatic profile are specific to each individual wine yeast strain

    Observables in 3d spinfoam quantum gravity with fermions

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    We study expectation values of observables in three-dimensional spinfoam quantum gravity coupled to Dirac fermions. We revisit the model introduced by one of the authors and extend it to the case of massless fermionic fields. We introduce observables, analyse their symmetries and the corresponding proper gauge fixing. The Berezin integral over the fermionic fields is performed and the fermionic observables are expanded in open paths and closed loops associated to pure quantum gravity observables. We obtain the vertex amplitudes for gauge-invariant observables, while the expectation values of gauge-variant observables, such as the fermion propagator, are given by the evaluation of particular spin networks.Comment: 32 pages, many diagrams, uses psfrag

    3d Spinfoam Quantum Gravity: Matter as a Phase of the Group Field Theory

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    An effective field theory for matter coupled to three-dimensional quantum gravity was recently derived in the context of spinfoam models in hep-th/0512113. In this paper, we show how this relates to group field theories and generalized matrix models. In the first part, we realize that the effective field theory can be recasted as a matrix model where couplings between matrices of different sizes can occur. In a second part, we provide a family of classical solutions to the three-dimensional group field theory. By studying perturbations around these solutions, we generate the dynamics of the effective field theory. We identify a particular case which leads to the action of hep-th/0512113 for a massive field living in a flat non-commutative space-time. The most general solutions lead to field theories with non-linear redefinitions of the momentum which we propose to interpret as living on curved space-times. We conclude by discussing the possible extension to four-dimensional spinfoam models.Comment: 17 pages, revtex4, 1 figur

    Photon-axion mixing and ultra-high-energy cosmic rays from BL Lac type objects -- Shining light through the Universe

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    Photons may convert into axion like particles and back in the magnetic field of various astrophysical objects, including active galaxies, clusters of galaxies, intergalactic space and the Milky Way. This is a potential explanation for the candidate neutral ultra-high-energy (E>10^18 eV) particles from distant BL Lac type objects which have been observed by the High Resolution Fly's Eye experiment. Axions of the same mass and coupling may explain also TeV photons detected from distant blazars.Comment: Revtex 10 pages, 6 figures. V.2: QED dispersion effects taken into account; principal results unchanged. V3: misprints and sqrt(4*pi) factors in Gauss to eV conversion corrected; conclusions unchange

    Emergent non-commutative matter fields from Group Field Theory models of quantum spacetime

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    We offer a perspective on some recent results obtained in the context of the group field theory approach to quantum gravity, on top of reviewing them briefly. These concern a natural mechanism for the emergence of non-commutative field theories for matter directly from the GFT action, in both 3 and 4 dimensions and in both Riemannian and Lorentzian signatures. As such they represent an important step, we argue, in bridging the gap between a quantum, discrete picture of a pre-geometric spacetime and the effective continuum geometric physics of gravity and matter, using ideas and tools from field theory and condensed matter analog gravity models, applied directly at the GFT level.Comment: 13 pages, no figures; uses JPConf style; contribution to the proceedings of the D.I.C.E. 2008 worksho

    Coupling gauge theory to spinfoam 3d quantum gravity

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    We construct a spinfoam model for Yang-Mills theory coupled to quantum gravity in three dimensional riemannian spacetime. We define the partition function of the coupled system as a power series in g_0^2 G that can be evaluated order by order using grasping rules and the recoupling theory. With respect to previous attempts in the literature, this model assigns the dynamical variables of gravity and Yang-Mills theory to the same simplices of the spinfoam, and it thus provides transition amplitudes for the spin network states of the canonical theory. For SU(2) Yang-Mills theory we show explicitly that the partition function has a semiclassical limit given by the Regge discretization of the classical Yang-Mills action.Comment: 18 page
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