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Topic: Effective field theories

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Particle physics

	Effective field theory - Wikipedia, the free encyclopedia
		In physics, an effective field theory is an approximate theory (usually a quantum field theory) that contains the appropriate degrees of freedom to describe physical phenomena occurring at a chosen length scale, but ignores the substructure and the degrees of freedom at shorter distances (or, equivalently, higher energies).
		The theory had great phenomenological success and was eventually understood to arise from the gauge theory of electroweak interactions, which forms a part of the standard model of particle physics.
		One major branch of nuclear physics is quantum hadrodynamics, where the interactions of hadrons are treated as a field theory, which one hopes to derive from quantum chromodynamics, the true underlying theory, in the future.
	en.wikipedia.org /wiki/Effective_field_theory (777 words)

	Quantum field theory - Wikipedia, the free encyclopedia
		Non-relativistic quantum field theories are needed in condensed matter physics— for example in the BCS theory of superconductivity.
		Relativistic quantum field theories are indispensable in particle physics (see the standard model), although they are known to arise as effective field theories in condensed matter physics.
		Classical field theory is the same as classical mechanics of an infinite number of dynamical quantities (say, tiny elements of rubber on a rubber sheet).
	en.wikipedia.org /wiki/Quantum_field_theory (3491 words)

	Effective field theory -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-08)
		Nevertheless, this approximation is often good enough to understand all processes whose typical distance scale is longer than the scale of the effective field theory or whose exchanged energy is smaller than the chosen bound.
		More generally, the transition between different effective field theories and the dependence of its parameters on the length scale in particular is described by the (additional info and facts about renormalization group) renormalization group.
		The effective theory appropriate to this situation is the soft-collinear effective theory.
	www.absoluteastronomy.com /encyclopedia/e/ef/effective_field_theory.htm (216 words)

	Encyclopedia: Effective field theory (Site not responding. Last check: 2007-10-08)
		In physics, the adjective renormalizable refers to a theory (usually a quantum field theory) in which all ultraviolet divergences, infinities and other seemingly meaningless results can be cured by the process of renormalization.
		Chiral perturbation theory is an effective field theory constructed on a lagrangian consistent with the (approximate) chiral symmetry of quantum chromodynamics.
		Quantum gravity is the field of theoretical physics attempting to unify the theory of quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity.
	www.nationmaster.com /encyclopedia/Effective-field-theory (1773 words)

	GLOSSARY
		In quantum theory for example it is well known that you may change the phase of the wave functions by an arbitrary amount without altering any the physical content or structure of the theory, provided that you change the all wave functions in the same way, everywhere in space.
		This theory is called M theory (it is not even known what the M stands for!) and has 11 dimensional supergravity as its low energy effective theory.
		Sting theories (there are five consistent string theories known) are quantum theories where the underlying object is a one dimensional string in spacetime (as opposed to particles in quantum field theories).
	www.mth.kcl.ac.uk /~lambert/glossary0.html (1689 words)

	Symmetry and Symmetry Breaking
		That is, the effective Lagrangian obeys symmetries that are not symmetries of the underlying theory.
		The prototype case is the 1928 Heisenberg theory of the ferromagnet as an infinite array of spin 1/2 magnetic dipoles, with spin-spin interactions between nearest neighbours such that neighbouring dipoles tend to align.
		In such theories as the unified model of electroweak interactions, the SSB responsible (via the Higgs mechanism) for the masses of the gauge vector bosons is because of the symmetry-violating vacuum expectation values of scalar fields (the so-called Higgs fields) introduced ad hoc in the theory.
	plato.stanford.edu /entries/symmetry-breaking (9818 words)

	[No title] (Site not responding. Last check: 2007-10-08)
		The study of nonlinear optical pulse propagation using effective field equations, such as the nonlinear Schroedinger equation and the nonlinear coupled mode equations, has been an active area of research in 1D photonic crystals, or "gratings," for the past fifteen years.
		Unfortunately, while reasonably rigourous derivations of such effective field equations for structures with large variations in their linear optical properties have been performed, they are complicated and do not allow a simple understanding of the conservation laws that the final equations exhibit.
		This research field is full of challenges, both with respect to identifying the correct effective field equations and in characterizing their solutions.
	www.math.toronto.edu /appmath/AppMath_02_03/sipe.html (209 words)

	Effective field theories in nuclear and atomic physics (Site not responding. Last check: 2007-10-08)
		Effective field theories in nuclear and atomic physics
		Effective field theories allow to accurately and systematically analyze the properties of few-body systems.
		We calculate the forces between 2, 3, and 4 nucleons in chiral effective field theory and at low energies in the framework of pionless EFT, based on contact interactions.
	www.itkp.uni-bonn.de /eftka_e.html (136 words)

	Not Even Wrong » Blog Archive » Into the Swampland
		He gives various arguments for why certain effective field theories may not correspond to string theories, but most of these are just something like “the string theory constructions we have looked at so far can’t give this kind of effective field theory”.
		Most of the examples he gives of effective theories that may not be low energy limits of a string theory are gauge theories of high rank.
		If one understands the types of effective field theories string theory cannot produce, and shows that e.g., our universe is governed by an effective field theory that is not stringy, then we can move string theory entirely to the math.
	www.math.columbia.edu /~woit/wordpress/?p=265 (2632 words)

	Relativistic Mean-field Theories (Site not responding. Last check: 2007-10-08)
		High energy physicists have been trying for already a few dozen of years to apply the formalism of the quantum field theory to the problem of the atomic nucleus.
		It is certainly a paradox that some of the weaknesses of the RMF theory comes from its self-consistent character: this is due to the fact that many approximations are made, which can not be said to be kept under control.
		In rotating nuclei, the J1 and J2 moments of inertia as well as effective alignments between Yrast bands in the region of mass A=150 allowed to determine from the first time the amount of pairing which is necessary at high spins.
	ireswww.in2p3.fr /ires/recherche/theorie/en_node2.html (477 words)

	Renormalization of quantum field theories with periodic field variables (I.Nándori, J.Polonyi, and K. Sailer) (Site not responding. Last check: 2007-10-08)
		Our goal is to investigate the low-energy effective theory for a model in which the self-interaction is given by a periodic potential at the UV scale.
		Renormalization of field theories with periodic variables represents a double challenge.
		We have shown on the example of the two-dimensional Euclidean one-component scalar field theory with periodic self-interaction that in both phases of the theory the blocked potential flattens out to provide a constant effective potential in the IR limit [2].
	dtp.atomki.hu /HOME-PAGE/progr2002/node14.html (419 words)

	FIELD THEORIES IN SUMMARY
		In between the dynamic and relational types are the field theories of Mey and Mannheim, which view the field as a manifold of tensions, forces, and powers standing in momentary balance or equilibrium.
		A third observation regarding field theories is that those (Lewin, Brown, and Mey) who apply field conceptions developed at the psychological level to the sociocultural sphere do not make the transformation or transition form one level to another clear.
		That is, field theorists have been methodologically unsophisticated and have been particularly weak in the very multivariate methods, such as principal components analysis, that could be most integrated into the structure of their theories.
	www.hawaii.edu /powerkills/DPF.CHAP6.HTM (1919 words)

	Session CC - Nuclear Theory II.
		An alternative approach to the microscopic interpretation derives a mean field theory from the algebraic model.
		The states of the mean field theory are a single orbit of the collective motion group in Fock space.
		Specifically, the first and second moments of the effective interaction are estimated via random matrices and then used to generate a statistical effective interaction which approximates the exact effective interaction.
	flux.aps.org /meetings/YR97/BAPSDNP97/abs/S2300.html (1175 words)

	Effective Field Theories and Effective Interactions (Site not responding. Last check: 2007-10-08)
		The situation is salvaged by effective field theory, which provides a connection between conventional nuclear physics and QCD.
		It is quite conceivable that the coupling constants in a rigorous effective pion-nucleon theory could be determined from lattice QCD simulations.
		The purpose of this program is to bring together physicists in these three fields so that they can share their expertise in effective field theory and further its application to problems in nuclear physics.
	int.phys.washington.edu /PROGRAMS/INT-00-2program.html (315 words)

	EFFECTIVE FIELD THEORIES OF QCD, BAD HONNEF/GERMANY
		The aim of the workshop is to bring together theorists working on various aspects of effective field theories (EFT) of QCD.
		High precision calculations of chiral perturbation theory (CHPT) in the mesonic and one-baryon sector of low-energy QCD should be developed further (radiative corrections, bound states, strangeness, etc.).
		The aim is to apply EFT methods in the regime of extreme densities where there is an interplay between perturbative (asymptotic freedom) and non-perturbative (color-superconductivity) physics.
	www.fz-juelich.de /ikp/QCD_FirstAnnouncement.html (266 words)

	Re: Effective Field Theory
		In article <3AA63C59.29463CC3@unine.ch>, Bagnoud Maxime wrote: > Bill Hobba wrote: > > I have been going though Weinberg Quantum Theory of Fields > > > > I have noticed he uses the Effective Field Theory approach where the cutoff > > is not taken to infinity.
		Weinberg was probably the first to systematize the modern view of field theories as 'effective field theories', but various effective field theories were already in use in the 1930s.
		The Fermi theory of beta decay uses an effective four-fermion coupling based on the tree-level diagrams of an intermediate vector boson theory, as everyone knows.
	www.lns.cornell.edu /spr/2001-03/msg0031774.html (306 words)

	2nd Announcement: EFFECTIVE FIELD THEORIES 2004, BAD HONNEF/GERMANY (Site not responding. Last check: 2007-10-08)
		Effective Field Theories in Nuclear, Particle and Atomic Physics
		This workshop organized by the WE-Heraeus-Stiftung, the Helmholtz-Institut für Strahlen-und Kernphysik (Theory Department) of the Bonn University, and the Forschungszentrum Jülich, is a continuation and extension of a series of workshops started at Dobogókö/Hungary in 1991.
		The aim of the workshop is to bring together theorists working on various aspects of effective field theories (EFT) in Nuclear, Particle and Atomic Physics.
	www.itkp.uni-bonn.de /~eft04/EFT04_SecondAnnouncement.html (330 words)

	PhysicsWeb - Events - International School in "Applications of Effective Field Theories"
		The school is aimed at introducing PhD students and postdoctoral fellows to the basic tools in modern Effective Field Theories techniques and to a broad and rich overview of the applications of these techniques.
		Applications to several different physics fields will be discussed, ranging from high energy physics to condensed matter, from nuclear physics to string theory, from computational physics to quantum mechanics.
		The goal of the school is to give the students the necessary theoretical background and understanding of the current and new effective field theories techniques to be able to actively participate in the research in these fields and to have the tools to start new research of this type in their own field.
	physicsweb.org /events/2419 (186 words)

	Quantum Overview/2
		The heaviest of these was predicted by Stephen Weinberg in a theory which unites electromagnetism and the weak force in a single super-force in which three of the particles have gained a large rest mass by a process called symmetry-breaking, but are otherwise sister particles of the photon.
		In the case of electromagnetism this is the phase of the wave and in gravity it is the relativistic transformations of space-time.
		Supersymmetric theories are usually developed in higher dimensional spaces in the form of string theories, in which particles become harmonically excitable strings of perhaps 10 to 12 dimensions at very small distance scales.
	www.dhushara.com /book/quantcos/quant1/quantsb.htm (3102 words)

	Home page of Bira van Kolck
		is on Effective Field Theories (EFTs), in particular their applications to problems at the interface between particle and nuclear physics, and to problems in molecular physics.
		EFTs separate the energy scales in a physical system, and use their small ratios as parameters for controlled expansions of low-energy observables, even in the presence of strong interactions among many bodies.
		: Nuclear Physics with Effective Field Theory, held at Caltech in February 1998, and Nuclear Physics with Effective Field Theory: 1999, held at the INT in February 1999.
	www.physics.arizona.edu /~vankolck (992 words)

	PhilSci Archive - Reductionism, Emergence, and Effective Field Theories (Site not responding. Last check: 2007-10-08)
		Castellani, Elena (2000) Reductionism, Emergence, and Effective Field Theories.
		In recent years, a change in attitude in particle physics has led to our understanding current quantum field theories as effective field theories (EFTs).
		In particular, it is a purpose of this paper to clarify how EFTs may provide an interesting case-study in current philosophical discussion on reduction, emergence and inter-level relationships in general.
	philsci-archive.pitt.edu /archive/00000106 (120 words)

	[No title]
		Methods will be discussed how to compute an effective low energy action from a given fundamental action, either analytically or numerically, or by a combination of both methods.
		The blockspin need not be a field of the same type as one of the fundamental fields, and it may be composite.
		Numerical methods are applicable to obtain actions of effective theories on lattices of finite volume.
	casper.cs.yale.edu /mgnet/www/mgnet/digests/V2N06 (1073 words)

	[No title] (Site not responding. Last check: 2007-10-08)
		Effective field theories have proven invaluable in controlling these uncertainties.
		However, canonical effective field theories are often insufficient in cases where experimental cuts, necessary to remove backgrounds, force theory into corners of phase space.
		In such, cases we must design an effective field theory which is particular to the case under study.
	www-physics.lbl.gov /seminars/old/rothstein.html (141 words)

	Seminar Abstract (Site not responding. Last check: 2007-10-08)
		Effective field theories explore a separation of scales in order to describe low-energy phenomena, using the ratios of small-to-large scales as controlled expansion parameters, even if no small coupling constants exist.
		Particularly interesting are systems ---such as nucleons or 4He atoms--- where two particles form a (real or virtual) bound state ---such as the deuteron or the 4He dimer--- that is much larger than the range of the interaction.
		We discuss the surprising properties of effective field theories applicable to this class of systems, in particular the limit-cycle behavior of three-body forces.
	www.public.iastate.edu /~npthy/seminar/abs_kolck.html (130 words)

	Solving RGEs in Effective Field Theories [Kristjan Kannike] (Site not responding. Last check: 2007-10-08)
		At a threshold, parameters of the theories below and above it are matched.
		Between thresholds, the dependence of parameters such as couplings, masses, or mixing angles is described by renormalization group equations (RGEs).
		Solving RGEs in EFTs version 1.5 as a Mathematica 5 notebook (freely available under the GNU General Public License).
	www.physic.ut.ee /~kkannike/english/science/physics/RGE_run_EFT/index.html (771 words)

	Sub Pages (Site not responding. Last check: 2007-10-08)
		Their nonlinear properties will therefore be characterized by soliton and solitary-wave like effects, should be of interest from the fundamental perspective of nonlinear dynamics, and may be of use in switching operations for telecommunication applications.
		Despite the fact that the index contrast of the constituent materials in these structures can be quite large, and varies on the order of the wavelength of light, realistic effective field theories for these materials can be developed for the propagation of pulses of light whose length is many times the lattice period.
		We describe one approach to constructing such theories, based on a canonical description of the electromagnetic field, that allows for an easy construction of conserved quantities and their relation to the symmetries of the system.
	www.math.utah.edu /etopim/text/abstracts/sipe.html (222 words)

	Effective Field Theories (ResearchIndex) (Site not responding. Last check: 2007-10-08)
		Abstract: Effective field theories encode the predictions of a quantum field theory at low energy.
		As a result, loop corrections are small, at least if the effective action contains a term which is quadratic in the fields, and physical predictions can be read straight from the effective Lagrangean.
		Methods will be discussed how to compute an effective low energy action from a given fundamental action, either analytically or numerically, or by a...
	citeseer.csail.mit.edu /203069.html (459 words)

	Gauge Field Theories (Cambridge Monographs on Mathematical Physics)
		Beginning with a new chapter giving a systematic introduction to classical field theories and a short discussion of their canonical quantization and the discrete symmetries C, P and T, the book provides a brief exposition of perturbation theory, the renormalization programme, and the use of the renormalization group equation.
		His treatment of functional integrals is one of the best I've seem in a field theory textbook and he does a better job of deriving the Feynman rules for QCD than I have seen elsewhere.
		If i taught field theory i think this would be an ideal second semester book, first semester something more mundane.
	www.literacyconnections.com /0_0521478162.html (427 words)

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