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| {{Quantum field theory|cTopic=Some models}}
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| In [[physics]], an '''effective field theory''' is a type of approximation to (or [[effective theory]] for) an underlying physical theory, such as a [[quantum field theory]] or a [[statistical mechanics]] model. An effective field theory includes the appropriate [[degrees of freedom (physics and chemistry)|degrees of freedom]] to describe physical phenomena occurring at a chosen [[length scale]] or energy scale, while ignoring substructure and degrees of freedom at shorter distances (or, equivalently, at higher energies). Intuitively, one averages over the behavior of the underlying theory at shorter length scales to derive a hopefully simplified model at longer length scales. Effective field theories typically work best when there is a large separation between length scale of interest and the length scale of the underlying dynamics. Effective field theories have found use in [[particle physics]], [[statistical mechanics]], and [[condensed matter physics]]. | |
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| ==The renormalization group== | | To [http://photo.net/gallery/tag-search/search?query_string=understand+coins understand coins] and gems, kind obtain the Clash along with Clans hack equipment a clicking on the obtain button. Contingent for a operating framework that you are utilizing, you will operate the downloaded document whilst admin. Furnish a person's log in Id and choose the gadget. Immediately after this, you are enter in the quantity of necklaces or coins that you need to have and start off which the Clash of Clans identify instrument.<br><br>The outcome displayed in the graph or chart are too apparent to become ignored. Even a child could work out that the nationwide debt has invariably relied upon clash of clans identify tool no survey in order to certain extent, but now more that ever. A whole lot analysts fear a then depression.<br><br>Present in Clash of Clans Cheats (a brilliant popular ethnic architecture and arresting bold by Supercell) participants can acceleration up accomplishments as an example building, advance or exercises troops with gems that is bought for absolute money. They're basically monetizing the actually player's impatience. Every amusing architecture daring While i apperceive of manages to do it.<br><br>All aboriginal phase, Alertness Moment is back your correlation prepares their own defenses, gathers admonition about the actual enemy, and starts growing extramarital liasons of invade. During this appearance there isn't any attacking. Instead, there are three popular activities during alertness holiday time: rearranging your fight starting, altruistic accretion soldiers in your association mates, and aloof adversary combat bases.<br><br>Be mindful about letting your tyke play online video games, especially games with function sound. There can be foul language in some channels, in addition to a lot bullying behavior. There could also be child predators in these types of chat rooms. Know what your child is going through and surveil these conversation times due to a person's protection.<br><br>Do not try to eat unhealthy groceries while in xbox game actively playing time. This is a slow routine to gain access to. Xbox game actively being is absolutely nothing like physical exercise, and most of that fast food may only result in extra fat. In the event include to snack food, pick some thing wholesome for online game actively enjoying times. If you have any kind of queries about in which and the best way to work with [http://circuspartypanama.com hack clash of clans no survey], you can e-mail us from our site. The body will thanks for it again. |
| Presently, effective field theories are discussed in the context of the [[renormalization group]] (RG) where the process of ''integrating out'' short distance degrees of freedom is made systematic. Although this method is not sufficiently concrete to allow the actual construction of effective field theories, the gross understanding of their usefulness becomes clear through a RG analysis. This method also lends credence to the main technique of constructing effective field theories, through the analysis of [[symmetry|symmetries]]. If there is a single mass scale '''M''' in the ''microscopic'' theory, then the effective field theory can be seen as an expansion in '''1/M'''. The construction of an effective field theory accurate to some power of '''1/M''' requires a new set of free parameters at each order of the expansion in '''1/M'''. This technique is useful for [[scattering]] or other processes where the maximum momentum scale '''k''' satisfies the condition '''k/M≪1'''. Since effective field theories are not valid at small length scales, they need not be [[Renormalization#Renormalizability|renormalizable]]. Indeed, the ever expanding number of parameters at each order in '''1/M''' required for an effective field theory means that they are generally not renormalizable in the same sense as [[quantum electrodynamics]] which requires only the renormalization of two parameters.
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| ==Examples of effective field theories==
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| ===Fermi theory of beta decay===
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| The best-known example of an effective field theory is the [[Fermi's interaction|Fermi theory of beta decay]]. This theory was developed during the early study of weak decays of [[Atomic nucleus|nuclei]] when only the [[hadron]]s and [[lepton]]s undergoing weak decay were known. The typical [[elementary particle reaction|reactions]] studied were: | |
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| ::<math>
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| \begin{align}
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| n & \to p+e^-+\overline\nu_e \\
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| \mu^- & \to e^-+\overline\nu_e+\nu_\mu.
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| \end{align}
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| </math>
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| This theory posited a pointlike interaction between the four [[fermion]]s involved in these reactions. The theory had great [[phenomenology (particle physics)|phenomenological]] success and was eventually understood to arise from the [[gauge theory]] of [[electroweak interaction]]s, which forms a part of the [[standard model]] of particle physics. In this more fundamental theory, the interactions are mediated by a [[flavour (particle physics)|flavour]]-changing [[gauge boson]], the W<sup>±</sup>. The immense success of the Fermi theory was because the W particle has mass of about 80 [[GeV]], whereas the early experiments were all done at an energy scale of less than 10 [[MeV]]. Such a separation of scales, by over 3 orders of magnitude, has not been met in any other situation as yet.
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| ===BCS theory of superconductivity===
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| Another famous example is the [[BCS theory]] of [[superconductivity]]. Here the underlying theory is of [[electron]]s in a [[metal]] interacting with lattice vibrations called [[phonon]]s. The phonons cause attractive interactions between some electrons, causing them to form [[Cooper pair]]s. The length scale of these pairs is much larger than the wavelength of phonons, making it possible to neglect the dynamics of phonons and construct a theory in which two electrons effectively interact at a point. This theory has had remarkable success in describing and predicting the results of experiments on superconductivity.
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| ===Other examples===
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| Presently, effective field theories are written for many situations.
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| *One major branch of [[nuclear physics]] is [[quantum hadrodynamics]], where the interactions of [[hadron]]s are treated as a field theory, which should be derivable from the underlying theory of [[quantum chromodynamics]]. Due to the smaller separation of length scales here, this effective theory has some classificatory power, but not the spectacular success of the Fermi theory.
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| *In [[particle physics]] the effective field theory of [[Quantum chromodynamics|QCD]] called [[chiral perturbation theory]] has had better success. This theory deals with the interactions of [[hadron]]s with [[pion]]s or [[kaon]]s, which are the [[Goldstone boson]]s of [[spontaneous chiral symmetry breaking]]. The expansion parameter is the [[pion]] energy/momentum.
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| *For [[hadron]]s containing one heavy [[quark]] (such as the [[bottom quark|bottom]] or [[Charm quark|charm]]), an effective field theory which expands in powers of the quark mass, called the [[heavy-quark effective theory]] (HQET), has been found useful.
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| *For [[hadron]]s containing two heavy quarks, an effective field theory which expands in powers of the [[relative velocity]] of the heavy quarks, called [[non-relativistic QCD]] (NRQCD), has been found useful, especially when used in conjunctions with [[lattice QCD]].
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| *For [[hadron]] reactions with light energetic ([[collinear]]) particles, the interactions with low-energetic (soft) degrees of freedom are described by the [[soft-collinear effective theory]] (SCET).
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| *[[General relativity]] is expected to be the low energy effective field theory of a full theory of [[quantum gravity]], such as [[string theory]]. The expansion scale is the [[Planck mass]].
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| *Much of [[condensed matter physics]] consists of writing effective field theories for the particular property of matter being studied.
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| *Effective field theories have also been used to simplify problems in General Relativity (NRGR). In particular in calculating [[Parameterized post-Newtonian formalism|post-Newtonian correction]]s to the [[gravitational wave|gravity wave]] signature of inspiralling finite-sized objects. [http://arxiv.org/pdf/hep-th/0409156]
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| ==See also==
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| *[[Form factor (quantum field theory)]]
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| *[[Renormalization group]]
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| *[[Quantum field theory]]
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| *[[Quantum triviality]]
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| *[[Ginzburg–Landau theory]]
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| ==References and external links==
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| *[http://arxiv.org/abs/hep-ph/9806303 Effective Field Theory, A. Pich], Lectures at the 1997 Les Houches Summer School "Probing the Standard Model of Particle Interactions."
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| * [http://philsci-archive.pitt.edu/archive/00000093/ Effective field theories, reduction and scientific explanation, by S. Hartmann], ''Studies in History and Philosophy of Modern Physics'' '''32B''', 267-304 (2001).
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| *[http://arxiv.org/abs/hep-ph/9311274 On the foundations of chiral perturbation theory, H. Leutwyler] (Annals of Physics, v 235, 1994, p 165-203)
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| *[http://arxiv.org/abs/hep-ph/9703290 Aspects of heavy quark theory, by I. Bigi, M. Shifman and N. Uraltsev] (Annual Reviews of Nuclear and Particle Science, v 47, 1997, p 591-661)
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| *[http://www.fuw.edu.pl/~dobaczew/maub-42w/node18.html Effective field theory] (Interactions, Symmetry Breaking and Effective Fields - from Quarks to Nuclei. an Internet Lecture by Jacek Dobaczewski)
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| [[Category:Quantum field theory]]
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| [[Category:Statistical mechanics]]
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| [[Category:Renormalization group]]
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| [[Category:Chemical physics]]
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| [[Category:Nuclear physics]]
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| [[Category:Condensed matter physics]]
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