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Search Results: 1 - 10 of 298782 matches for " J. Andersen "
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The Free Energy in Scalar Electrodynamics at High Temperature
J. O. Andersen
Physics , 1997,
Abstract: Massless scalar electrodynamics is studied at high temperature and zero chemical potential. I derive the free energy to order $\lambda^2$, $\lambda e^2$ and $e^4$ by effective field theory methods. The first step consists of the construction of an effective three-dimensional field theory that is valid on distance scales $R\gg 1/T$ and whose parameters can be written as power series in $\lambda$ and $e^2$. These coupling constants encode the contribution to physical quantities from the scale $T$. The second step is the use of the effective Lagrangian and perturbative calculations yield the contributions to the free energy from the scale $eT\sim\sqrt{\lambda}T$.
On Effective Field Theories at Finite Temperature
J. O. Andersen
Physics , 1997,
Abstract: Chapter one is devoted to a study of fermions and bosons in two spatial dimensions in external electromagnetic fields. The effectve action is calculated by integrating out the matter fields. In chapter two, I investigate the resummation program of Braaten and Pisarski. I calculate the screening mass squared and the free energy in Yukwava theory to two and three-loop order, respectively, in resummed perturbation theory. The main part of the present work is on effective field theories at finite temperature. I discuss the concepts of dimensional reduction, modern renormalization theory, and renormalizable field theories (``fundamental theories'') versus non-renormalizable theories (``effective theories''). Two methods for constructing effective three dimensional field theories are discussed. The first is based on the effective potential, and is applied to field theory with $N$ charged U(N) symmetric scalar coupled to an Abelian gauge field. The second method is an effective field theory approach based on diagrammatical methods, recently developed by Braaten and Nieto. I apply the methods to various problems in spinor and scalar QED.
The Screening Mass Squared in Hot Scalar Theory to Order $g^5$ Using Effective Field Theory
J. O. Andersen
Physics , 1997, DOI: 10.1103/PhysRevD.57.5004
Abstract: We study massless $g^2\Phi^4$-theory at high temperature and with zero chemical potential. Using modern effective field theory methods,% recently developed by Braaten and Nieto, we derive the screening mass squared to order $g^5$. It is demonstrated that the result is renormalization group invariant to this order in the coupling constant. Renormalization group methods are used to sum up leading logarithms of $g$.
Predicting Failure using Conditioning on Damage History: Demonstration on Percolation and Hierarchical Fiber Bundles
J. Andersen,D. Sornette
Physics , 2005, DOI: 10.1103/PhysRevE.72.056124
Abstract: We formulate the problem of probabilistic predictions of global failure in the simplest possible model based on site percolation and on one of the simplest model of time-dependent rupture, a hierarchical fiber bundle model. We show that conditioning the predictions on the knowledge of the current degree of damage (occupancy density $p$ or number and size of cracks) and on some information on the largest cluster improves significantly the prediction accuracy, in particular by allowing to identify those realizations which have anomalously low or large clusters (cracks). We quantify the prediction gains using two measures, the relative specific information gain (which is the variation of entropy obtained by adding new information) and the root-mean-square of the prediction errors over a large ensemble of realizations. The bulk of our simulations have been obtained with the two-dimensional site percolation model on a lattice of size $L \times L=20 \times 20$ and hold true for other lattice sizes. For the hierarchical fiber bundle model, conditioning the measures of damage on the information of the location and size of the largest crack extends significantly the critical region and the prediction skills. These examples illustrate how on-going damage can be used as a revelation of both the realization-dependent pre-existing heterogeneity and the damage scenario undertaken by each specific sample.
The Witten-Reshetikhin-Turaev invariants of finite order mapping tori I
J?rgen Ellegaard Andersen
Mathematics , 2011,
Abstract: We formulate the Asymptotic Expansion Conjecture for the Witten-Reshetikhin-Turaev quantum invariants of closed oriented three manifolds. For finite order mapping tori, we study these quantum invariants via the geometric gauge theory approach to the corresponding quantum representations and prove, using a version of the Lefschetz-Riemann-Roch Theorem due to Baum, Fulton, MacPherson and Quart, that the quantum invariants can be expressed as a sum over the components of the moduli space of flat connections on the mapping torus. Moreover, we show that the term corresponding to a component is a polynomial in the level $k$, weighted by a complex phase, which is $k$ times the Chern-Simons invariant corresponding to the component. We express the coefficients of these polynomials in terms of cohomological pairings on the fixed point set of the moduli space of flat connections on the surface. We explicitly describe the fixed point set in terms of moduli spaces of the quotient orbifold Riemann surface and for the smooth components we express the aforementioned coefficients in terms of the known generators of the cohomology ring. We provide an explicit formula in terms of the Seifert invariants of the mapping torus for the contributions from each of the smooth components. We further establish that the Asymptotic Expansion Conjecture and the Growth Rate Conjecture for these finite order mapping tori.
Mapping class group invariant unitarity of the Hitchin connection over Teichmüller space
J?rgen Ellegaard Andersen
Mathematics , 2012,
Abstract: We provide a geometric construction of the unitary structure which is projectively preserved by the Hitchin connection. We analyze the asymptotic behavior of it and we establish that it is uniformly in the level equivalent to the Hermitian structure induced by the L2 inner product on smooth sections.
A geometric formula for the Witten-Reshetikhin-Turaev Quantum Invariants and some applications
J?rgen Ellegaard Andersen
Mathematics , 2012,
Abstract: We provide a geometric construction of the boundary states for handlebodies which we in turn use to give a geometric formula for the Witten-Reshetikhin-Turaev quantum invariants. We then analyze the asymptotics of this invariant in the special case of a three manifold given by 1-surgery on a knot and we show that if the knot has an irreducible representation of its fundamental group into SU(2), then its quantum invariant cannot equal those of the three sphere. From this we conclude that if a knot has the same colored Jones polynomials as the unknot, it must be the unknot.
Pressens pr sidenter - fra Satan til Messias
Hanne J?rndrup,Dorte Andersen
Journalistica : Tidskrift f?r Forskning i Journalistik , 2010,
Abstract: Journalistikken og historiefaget er i egen selvforst else discipliner, der beskriver verden, som den er. Journalister rapporterer fra nutiden, mens historikere fort ller os, hvordan fortiden var. Artiklen s tter sp rgsm lstegn ved denne arbejdsdeling, idet begge fag g r hinanden i bedene og langt ud over den blotte afrapportering fra verden. Trods forestillingen om et neutralt udgangspunkt har begge fag til tider overordentlig stor indflydelse p s vel samtidens som fremtidens politik. Artiklen diskuterer problemerne gennem pressens billeder af tre pr sidenter – Hussein, Milosevic og Obama. Form let er, at illustrere muligheden af kritisk refleksion i historieskrivning med en ny og bedre kobling af journalistikken og historiefaget.
Der lautlose Weg zur Walküre: von Nibelungenlied zu Prosaedda
Peter Hvilsh?j Andersen Vinilandicu
Brathair , 2009,
Abstract: Mit Ausgangspunkt in zwei Schriftlichkeitspostulaten wird die Nibelungensage einer extgenetischen Analyse unterzogen, die den Waltharius, das Nibelungenlied, die Prosaeedda und die Heldenlieder des Codex Regius berücksichtigt. Die Untersuchung konzentriert sich auf die Brynhildfigur. Es wird dafür argumentiert, dass alle vier Versionen in chronologischer Reihenfolge voneinander abh ngig sind. Geraldus schrieb am Ende des 9. Jahrhunderts eine Fabel von Burgunds Eingliederung in den westlichen Teil des Frankenreichs. Karl der Kahle und Ludwig der Deutsche dienten als Vorbilder für Waltharius und dessen Gegner Guntharius. Ein sterreichischer Dichter, vermutlich Konrad von Fu esbrunnen, schrieb eine Fortsetzung des Waltharius und gab Guntharius eine Ehefrau, in der die westgotische Prinzessin Brunechild mit der sizilianischen Normannenk nigin Konstanze zusammenschmolz. Er machte sie zu einer isl ndischen K nigin und gab ihr einen symbolischen Namen mit drei Konnotationen: Prüfen“, Brünne“ und Brunnen“. Unter dem eindeutigen Namen Brynhild wurde sie von Snorri zur Walküre erhoben. Snorris kurze Prosabearbeitung des Nibelungenlieds bildete die Grundlage der Heldenlieder.
Two-Loop Calculations in phi^4 Light-Front Field Theory
F. Antonuccio,J. O. Andersen
Physics , 1999,
Abstract: We perform a two-loop calculation in light-front phi^4 theory to determine the effective mass renormalization of the light-front Hamiltonian. The renormalization scheme adopted here is manifestly boost invariant, and yields results that are in perfect agreement with the explicitly covariant Feynman diagram approach.
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