8,896 research outputs found

    Spectrum of the Laplace-Beltrami Operator and the Phase Structure of Causal Dynamical Triangulation

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    We propose a new method to characterize the different phases observed in the non-perturbative numerical approach to quantum gravity known as Causal Dynamical Triangulation. The method is based on the analysis of the eigenvalues and the eigenvectors of the Laplace-Beltrami operator computed on the triangulations: it generalizes previous works based on the analysis of diffusive processes and proves capable of providing more detailed information on the geometric properties of the triangulations. In particular, we apply the method to the analysis of spatial slices, showing that the different phases can be characterized by a new order parameter related to the presence or absence of a gap in the spectrum of the Laplace-Beltrami operator, and deriving an effective dimensionality of the slices at the different scales. We also propose quantities derived from the spectrum that could be used to monitor the running to the continuum limit around a suitable critical point in the phase diagram, if any is found.Comment: 21 pages, 26 figures, 2 table

    Feynman rules for Gauss's law

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    I work on a set of Feynman rules that were derived in order to incorporate the constraint of Gauss's law in the perturbation expansion of gauge field theories and calculate the interaction energy of two static sources. The constraint is implemented via a Lagrange multiplier field, λ\lambda, which, in the case of the non-Abelian theory, develops a radiatively generated effective potential term. After analysing the contributions of various solutions for λ\lambda, the confining properties and the various phases of the theory are discussed.Comment: 18 pages, 10 figure

    Low-Dimensional Long-Range Topological Charge Structure in the QCD Vacuum

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    While sign-coherent 4-dimensional structures cannot dominate topological charge fluctuations in the QCD vacuum at all scales due to reflection positivity, it is possible that enhanced coherence exists over extended space-time regions of lower dimension. Using the overlap Dirac operator to calculate topological charge density, we present evidence for such structure in pure-glue SU(3) lattice gauge theory. It is found that a typical equilibrium configuration is dominated by two oppositely-charged sign-coherent connected structures (``sheets'') covering about 80% of space-time. Each sheet is built from elementary 3-d cubes connected through 2-d faces, and approximates a low-dimensional curved manifold (or possibly a fractal structure) embedded in the 4-d space. At the heart of the sheet is a ``skeleton'' formed by about 18% of the most intense space-time points organized into a global long-range structure, involving connected parts spreading over maximal possible distances. We find that the skeleton is locally 1-dimensional and propose that its geometrical properties might be relevant for understanding the possible role of topological charge fluctuations in the physics of chiral symmetry breaking.Comment: 4 pages RevTeX, 4 figures; v2: 6 pages, 5 figures, more explanations provided, figure and references added, published versio

    Center vortices as rigid strings

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    It is shown that the action associated with center vortices in SU(2) lattice gauge theory is strongly correlated with extrinsic and internal curvatures of the vortex surface and that this correlation persists in the continuum limit. Thus a good approximation for the effective vortex action is the action of rigid strings, which can reproduce some of the observed geometric properties of center vortices. It is conjectured that rigidity may be induced by some fields localized on vortices, and a model-independent test of localization is performed. Monopoles detected in the Abelian projection are discussed as natural candidates for such two-dimensional fields.Comment: 7 pages, 8 figures, RevTeX

    Geometry of percolating monopole clusters

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    We perform detailed measurements of the geometrical characteristics of the percolating cluster of the magnetic monopole currents in the confining phase of the lattice SU(2) gluodynamics. The Maximal Abelian projection is used to define the monopoles. The use of the geometrical language is motivated by recent observations that the full non-Abelian action associated with the monopoles corresponds to point-like particles on the currently available lattices. Scaling behavior of various quantities is observed.Comment: 3 pages, 4 figures, Lattice2002(topology

    Hadron Deformation and Form Factors from Lattice QCD

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    We review the current status of lattice QCD studies of the nucleon system. In particular, we focus on the determination of the shape of the nucleon by probing its wave function as well as by evaluating the N to Delta transition form factors.Comment: 14 pages, 8 figures. Talk presented at the Workshop "The Shape of Hadrons", Athens, Greece, 27-30 April 200

    Universality of Mixed Action Extrapolation Formulae

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    Mixed action theories with chirally symmetric valence fermions exhibit very desirable features both at the level of the lattice calculations as well as in the construction and implementation of the low energy mixed action effective field theory. In this work we show that when such a mixed action effective field theory is projected onto the valence sector, both the Lagrangian and the extrapolation formulae become universal in form through next to leading order, for all variants of discretization methods used for the sea fermions. Our conclusion relies on the chiral nature of the valence quarks. The result implies that for all sea quark methods which are in the same universality class as QCD, the numerical values of the physical coefficients in the various mixed action chiral Lagrangians will be the same up to lattice spacing dependent corrections. This allows us to construct a prescription to determine the mixed action extrapolation formulae for a large class of hadronic correlation functions computed in partially quenched chiral perturbation theory at the one-loop level. For specific examples, we apply this prescription to the nucleon twist--2 matrix elements and the nucleon--nucleon system. In addition, we determine the mixed action extrapolation formula for the neutron EDM as this provides a nice example of a theta-dependent observable; these observables are exceptions to our prescription.Comment: 36 pages, appendix on twisted mass sea fermions added, expanded discussion of NLO operators, version published in JHEP; typographical errors corrected in Eqs. (68) and (69

    Iterative Universal Rigidity

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    A bar framework determined by a finite graph GG and configuration p\bf p in dd space is universally rigid if it is rigid in any RD⊃Rd{\mathbb R}^D \supset {\mathbb R}^d. We provide a characterization of universally rigidity for any graph GG and any configuration p{\bf p} in terms of a sequence of affine subsets of the space of configurations. This corresponds to a facial reduction process for closed finite dimensional convex cones.Comment: 41 pages, 12 figure
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