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Quantum Field Theory (quantum + field_theory)
Selected AbstractsAlmost-anywhere theories: Reductionism and universality of emergenceCOMPLEXITY, Issue 6 2010Ignazio Licata Abstract Here, we aim to show that reductionism and emergence play a complementary role in understanding natural processes and in the dynamics of science explanation. In particular, we will show that the renormalization group,one of the most refined tools of Theoretical Physics,allows to understand the importance of emergent processes' role in Nature identifying them as universal organization processes, that is, they are scale independent. We can use the syntaxes of Quantum Field Theory and the processes of Spontaneous Symmetry Breaking as a trans-disciplinary theoretical scenario for many other forms of complexity, especially the biological and cognitive ones. © 2010 Wiley Periodicals, Inc. Complexity, 2010 [source] Quantum field theories coupled to supergravityFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 3 2008J. Große Abstract This article is devoted to the investigation of the interplay of supersymmetric Yang,Mills theories (SYM) and supergravity (SUGRA). The topic is studied from two points of view: Firstly from the point of view of AdS/CFT correspondence, which realises the coupling of four dimensional superconformal ,, = 4 SYM theory and ten dimensional type IIB SUGRA in a holographic way. In order to arrive at theories that resemble quantum chromodynamics (QCD) more closely, fundamental fields are introduced using probe D7-branes and non-trivial background configuration are considered. In particular supergravity solutions that are only asymptotically anti-de Sitter and break supersymmetry are used. This allows the description of spontaneous chiral symmetry breaking. The meson spectrum is calculated and the existence of an associated Goldstone mode is demonstrated. Moreover it is shown that highly radially excited mesons are not degenerate. Additionally instanton configurations on the D7-branes are investigated, which lead to a holographic description of the dual field theory's Higgs branch. Finally a holographic description of heavy-light mesons is developed, which are mesons consisting of quarks with a large mass difference, such that a treatment of B mesons can be achieved The second approach is the technique of so-called space-time dependent couplings (also known as "local couplings"), where coupling constants are promoted to external sources. This allows to explore the conformal anomaly of quantum field theories coupled to a classical gravity background. The technique is extended to the superfield description of ,, = 1 supergravity, a complete basis for the anomaly is given and the consistency conditions that arise from a cohomological treatment are calculated. Possible implications for an extension of Zamolodchikov's c -theorem to four dimensional supersymmetric quantum field theories are discussed. [source] Dynamical adjustment of propagators in Renormalization Group flowsANNALEN DER PHYSIK, Issue 3 2007M. Salmhofer Abstract A class of continuous renormalization group flows with a dynamical adjustment of the propagator is introduced and studied theoretically for fermionic and bosonic quantum field theories. The adjustment allows to include self,energy effects nontrivially in the denominator of the propagator and to adapt the scale decomposition to a moving singularity, and hence to define flows of Fermi surfaces in a natural way. These flows require no counterterms, but the counterterms used in earlier treatments can be constructed using them. The influence of propagator adjustment on the strong,coupling behaviour of flows is examined for a simple example, and some conclusions about the strong coupling behaviour of renormalization group flows are drawn. [source] Beyond Dialogue: The Role of Science Within TheologyDIALOG, Issue 3 2007Ernest L. Simmons Abstract:, The purpose of this article is to provide background overview and contemporary context for the theme of this issue of Dialog, the role of science within theology. Over the last fifty years, this role has primarily involved dialogue and the drive to mutual understanding. That discussion has now reached a new stage seeking to move beyond dialogue toward what some are referring to as hypothetical consonance. One of the most serious constructive proposals moving beyond dialogue is Creative Mutual Interaction (CMI), proposed by Robert John Russell. The first five ways he discusses in CMI specifically address the role of science in theological reflection. It is argued that these five ways will assist the reader in contextualing the discussion found in the articles in this issue. Elaboration of each way is given, concluding with a constructive theological example of the heuristic use of scientific concepts found in quantum field theory. [source] Field theory for biogeography: a spatially explicit model for predicting patterns of biodiversityECOLOGY LETTERS, Issue 1 2010James P. O'Dwyer Abstract Predicting the variation of biodiversity across the surface of the Earth is a fundamental issue in ecology, and in this article we focus on one of the most widely studied spatial biodiversity patterns: the species,area relationship (SAR). The SAR is a central tool in conservation, being used to predict species loss following global climate change, and is striking in its universality throughout different geographical regions and across the tree of life. In this article we draw upon the methods of quantum field theory and the foundation of neutral community ecology to derive the first spatially explicit neutral prediction for the SAR. We find that the SAR has three phases, with a power law increase at intermediate scales, consistent with decades of documented empirical patterns. Our model also provides a building block for incorporating non-neutral biological variation, with the potential to bridge the gap between neutral and niche-based approaches to community assembly. Ecology Letters (2010) 13: 87,95 [source] The graviton propagator with a non-conserved external generating sourceFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 11-12 2007E.B. Manoukian Abstract A novel general expression is obtained for the graviton propagator from Lagrangian field theory by taking into account the necessary fact that in the functional differential approach of quantum field theory, in order to generate non-linearities in gravitation and interactions with matter, the external source T,,, coupled to the gravitational field, should a priori not be conserved ,,T,,, 0, so variations with respect to its ten components may be varied independently. The resulting propagator is the one which arises in the functional approach and does not coincide with the corresponding time-ordered product of two fields and it includes so-called Schwinger terms. The quantization is carried out in a gauge corresponding to physical states with two polarization states to ensure positivity in quantum applications. [source] Linking physiological mechanisms of coherent cellular behaviour with more general physical approaches towards the coherence of lifeIUBMB LIFE, Issue 11 2006Laurent Jaeken Abstract Schrödinger pointed out that one of the most fundamental properties of life is its coherent behaviour. This property has been approached from a physiological point of view by Ling in his 'association-induction hypothesis' and extended by Pollack (gel-sol theory), by Chaplin and by Kaivarainen (detailed studies of cellular water). The question of coherence has also been attacked from general physics in three independent approaches: from non-linear thermodynamics (Fröhlich), from quantum field theory (Del Giudice and his group) and from quantum mechanics (Davydov). In this paper all these approaches are unified. The emerging picture constitutes a new paradigm of life. iubmb Life, 58: 642 - 646, 2006 [source] Clifford geometric parameterization of inequivalent vacuaMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 12 2001Bertfried Fauser Abstract We propose a geometric method to parameterize inequivalent vacua by dynamical data. Introducing quantum Clifford algebras with arbitrary bilinear forms we distinguish isomorphic algebras,as Clifford algebras,by different filtrations (resp. induced gradings). The idea of a vacuum is introduced as the unique algebraic projection on the base field embedded in the Clifford algebra, which is however equivalent to the term vacuum in axiomatic quantum field theory and the GNS construction in C* -algebras. This approach is shown to be equivalent to the usual picture which fixes one product but employs a variety of GNS states. The most striking novelty of the geometric approach is the fact that dynamical data fix uniquely the vacuum and that positivity is not required. The usual concept of a statistical quantum state can be generalized to geometric meaningful but non-statistical, non-definite, situations. Furthermore, an algebraization of states takes place. An application to physics is provided by an U (2)-symmetry producing a gap equation which governs a phase transition. The parameterization of all vacua is explicitly calculated from propagator matrix elements. A discussion of the relation to BCS theory and Bogoliubov,Valatin transformations is given. Copyright © 2001 John Wiley & Sons, Ltd. [source] Stripe fractionalization: the quantum spin nematic and the Abrikosov latticePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003J. Zaanen The cover picture of physica status solidi (b), taken from the Editor's Choice of this issue, shows a scheme of construction of the spin nematic ordered state and the topological interaction between spatially disconnected gauge defects. The gauge symmetry is broken by applying an external field B. The theory described in the paper [1] offers a potential explanation for recent observations of magnetic field induced antiferromagnetism in La1.9Sr0.1CuO4. The first author, Jan Zaanen, is Professor of Physics at the Instituut-Lorentz in Leiden where he works on quantum field theory in condensed matter physics, concentrating on problems in high- TC superconductivity, quantum magnetism, quantum liquid crystals, doped Mott insulators, and strongly correlated electron systems. This paper is an invited presentation from the European Conference Physics of Magnetism (PM'02), held in Pozna,, Poland, 1,5 July 2002. The proceedings of this conference are published in two parts: in the present issue of phys. stat. sol. (b) and in phys. stat. sol. (a) 196, No. 1 (2003). [source] | ||||||||||||||||