Power-flow study - Revision history

en>Wtshymanski: whups, already linked missed piped form

2015-01-10T20:37:03Z

whups, already linked missed piped form

← Older revision		Revision as of 22:37, 10 January 2015
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	<br><br>[http://www.google.de/url?url=https://www.facebook.com/~~HostgatorCoupons2015~~&rct=j&q=&esrc=s&sa=U&ei=~~tbPoVMviLJT7avHhguAE~~&ved=~~0CE8QFjAH~~&usg=~~AFQjCNGMfXBtFKtagCQBonkpSw115XIY_Q~~ google.de]~~I'm~~ a ~~45 years old~~ and ~~work at the~~ high ~~school ([http://www~~.~~express.Co.uk/search/Integrated+International/ Integrated International] Studies)~~.<br>~~In my spare time I try~~ to ~~learn French~~. ~~I've been there and look forward to returning sometime near future~~. ~~I like~~ to ~~read~~, ~~preferably~~ on ~~my kindle~~. ~~I like~~ to ~~watch Arrested Development~~ and ~~2 Broke Girls as well as documentaries about nature~~. ~~I like Conlanging~~.<br><br>~~Also visit my blog~~ ... [http://jeregselljechhb.wordpress.com/ Hostgator Discount Coupons]		Let's have a look on world's hosting business: Thousands and hundreds of webhosting spread worldwide and their company purpose is basic - to obtain acknowledged and make earnings. With a lot noise around the internet hosting industry, it is a tough task for us to get the right hosting. It's not too difficult for me to identify Hostgator - a hosting service that stood out from the rest with impressive attributes. Exactly what I am going to do in this post is to assess Hostgator hosting as well as disclosing the key of Hostgator success.<br><br><br><br>[http://www.google.de/url?url=https://www.facebook.com/Hostgator1CentCoupon&rct=j&q=&esrc=s&sa=U&ei=YrPoVIffDcjlaPK7gqAH&ved=0CDcQFjAD&usg=AFQjCNEaF1oaQ2ZM4hyK8cdEgpIbe3kxug google.de]In any internet company, we rely on excellent host to offer stable and trustworthy webhosting services. Hostgator gives timely and promising qualities. They invested a lot of cash for its servers which each of them using Dual Xeon servers with 4GB memory and IDE hard disk drives. These high rate servers provide high receptive uptime of up to 99.9 % without failure.<br><br>Hostgator offers a lot of packages to consumers. Virtually all the bundles offered are affordable. For example, Hostgator shared hosting are charged $4.95 monthly for the standard shared hosting packaged. At fees which begin from $9.95 yearly, you can take pleasure in much more compact packages which really come with a bunch of stuffs. There still have a lot bundles which providing more affordable rates, however if you begin to study and attempt Hostgator, you will feel that every dollar and cent you invested is simply not wasted. Do your own research on the features consisted of in every bundles Hostgator providing, then you can differentiate the distinctions with others packages provided by various other webhosting.<br><br>For exaple, Hostgator helps you to back up the web sites immediately and securely. You have the choice to host limitless domains, sub domains and FTP accounts. Of source, the attribute which mentioned simply now will not be offered if you are the basic hosting bundle subscriber.<br><br>Hostgator offers control panel. Out of so numerous internet hosts around the world, Hostgator's cpanel can be said winning the top position among them.<br><br>In regard to customer supports, Hostgator has a really strong consumer care group which working 24/7 to assist you deal with all types of problems pertinent to their items. You can either contact them through phone or live chat with them with internet. You can also email your issues to them. If you cherished this article and you would like to be given more info concerning [http://jeregselljechhb.wordpress.com/ Hostgator Discount Coupons] generously visit the website. They will feedback quickly without taking any fees. This is why previously, Hostgator still the finest choice for customers.<br><br>A final words for those who are starting - don't be scare by exactly what you are reviewing as developing a good site is not that hard. The work is in truth rather easy and direct as long as you're getting the right information. To get begun, you'll first require a domain name and a dependable hosting service.

83.110.73.175: /* Load flow */

2014-02-17T13:16:10Z

Load flow

← Older revision		Revision as of 15:16, 17 February 2014
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	~~{{Quantum field theory\|cTopic=Some models}}~~		<br><br>[http://www.google.de/url?url=https://www.facebook.com/HostgatorCoupons2015&rct=j&q=&esrc=s&sa=U&ei=tbPoVMviLJT7avHhguAE&ved=0CE8QFjAH&usg=AFQjCNGMfXBtFKtagCQBonkpSw115XIY_Q google.de]I'm a 45 years old and work at the high school ([http://www.express.Co.uk/search/Integrated+International/ Integrated International] Studies).<br>In my spare time I try to learn French. I've been there and look forward to returning sometime near future. I like to read, preferably on my kindle. I like to watch Arrested Development and 2 Broke Girls as well as documentaries about nature. I like Conlanging.<br><br>Also visit my blog ... [http://jeregselljechhb.wordpress.com/ Hostgator Discount Coupons]
	In [[physics]], '''Faddeev–Popov ghosts''' (also called '''ghost fields''') are additional [[field (physics)\|fields]] which are introduced into [[gauge theories\|gauge]] [[quantum field theory\|quantum field theories]] to maintain the consistency of the [[path integral formulation]]. They are named after [[Ludvig Faddeev]] and [[Victor Popov]].<~~ref~~>~~W. F. Chen.~~ [http://~~arxiv~~.~~org~~/~~abs~~/~~0803~~.~~1340v2 Quantum Field Theory and Differential Geometry]<~~/~~ref>~~

	There is also a more general meaning of the word "'''ghost'''" in [[theoretical physics]], which is discussed below (see ''[[#General ghosts in theoretical physics\|general ghosts in theoretical physics]]'').

	==~~Overcounting in Feynman path integrals=~~=
	The necessity for Faddeev–Popov ghosts follows from the requirement that in the [[path integral formulation]], [[quantum field theory\|quantum field theories]] should yield unambiguous, non-singular solutions. This is not possible when a [[gauge symmetry]] is present since there is no procedure for selecting any one solution from a range of physically equivalent solutions, all related by a gauge transformation. The problem stems from the path integrals overcounting field configurations related by gauge symmetries, since those correspond to the same physical state; the [[measure (mathematics)\|measure]] of the path integrals contains a factor which does not allow obtaining various results directly from the original [[Action (physics)\|action]] using the regular methods (e.g., [[Feynman diagram]]s). It is possible, however, to modify the action, such that the regular methods will be applicable by adding some additional fields, which break the gauge symmetry, which are called the ''ghost fields''. This technique is called the "Faddeev–Popov procedure" (see also [[BRST quantization]]). The ghost fields are a computational tool in that they do not correspond to any real particles in external states: they ''only'' appear as [[virtual particle]]s in Feynman diagrams – or as the ''absence'' of some gauge configurations. However they are necessary to preserve [[unitarity (physics)\|unitarity]].

	The exact form or formulation of ghosts is dependent on the particular [[Gauge fixing\|gauge]] chosen, although the same physical results are obtained with all the gauges. The [[Gauge fixing\|Feynman-'t Hooft gauge]] is usually the simplest gauge for this purpose, and is assumed for the rest of this article.

	==~~Spin-statistics relation violated~~==
	~~The Faddeev–Popov ghosts violate the [[spin-statistics relation]], which is another reason why they are often regarded as "non-physical" particles.~~

	For example, in [[Yang–Mills theory\|Yang–Mills theories]] (such as [[quantum chromodynamics]]) the ghosts are [[complex number\|complex]] [[scalar field theory\|scalar fields]] ([[spin (physics)\|spin]] 0), but they [[anticommutativity\|anti-commute]] (like [[fermions]]).

	~~In general, [[anticommutativity\|anti-commuting]] ghosts are associated with [[fermion]]ic symmetries, while [[commutativity\|commuting]] ghosts are associated with [[boson]]ic symmetries~~.

	~~==Gauge fields and associated ghost fields==~~
	~~Every gauge field has an associated ghost, and where the gauge field acquires a mass via the [[Higgs mechanism]~~]~~, the associated ghost field acquires the same mass (in the Feynman-~~'~~t Hooft gauge only, not true for other gauges).~~

	~~==Appearance in Feynman diagrams==~~
	~~In [[Feynman diagram]]s the ghosts appear as closed loops wholly composed of 3-vertices, attached to the rest of the diagram via~~ a ~~gauge particle~~ at ~~each 3-vertex. Their contribution to~~ the ~~[[S matrix\|S-matrix]] is exactly cancelled~~ (~~in the~~ [~~[Feynman gauge\|Feynman-'t Hooft gauge]]) by a contribution from a similar loop of gauge particles with only 3-vertex couplings or gauge attachments to the rest of the diagram~~. ~~(A loop of gauge particles not wholly composed of 3-vertex couplings is not cancelled by ghosts~~.~~) The opposite sign of the contribution of the ghost and gauge loops is due to them having opposite fermionic~~/~~bosonic natures. (Closed fermion loops have an extra −1 associated with them; bosonic loops don't.)~~

	~~==Ghost field Lagrangian==~~
	~~The Lagrangian for the ghost fields <math>c^a(x)\,<~~/~~math> in [[Yang–Mills theory\|Yang–Mills theories]] (where <math>a<~~/~~math> is an index in the adjoint representation of the [[gauge group]~~]) ~~is given by~~
	~~:<math>\mathcal{L}_\mathrm{ghost} = \partial_\mu \overline{c}^a\partial^\mu c^a + g f^{abc}(\partial^\mu\overline{c}^a) A_\mu^b c^c~~. <~~/math~~>
	~~The first term is a kinetic term like for regular complex scalar fields, and the second term describes the interaction with the [[gauge field]]s~~. ~~Note that in~~ '~~'abelian'' gauge theories (such as [[quantum electrodynamics]]) the ghosts do not have any effect since <math>f^{abc} = 0</math>~~ and~~, consequently, the ghost particles do not interact with the gauge fields~~.

	~~==General ghosts in theoretical physics==~~
	~~The Faddeev–Popov ghosts are sometimes referred~~ to ~~as "good ghosts". The "bad ghosts" represent another~~, more general meaning of the word "ghost" in [[theoretical physics]]: states of negative norm—or fields with the wrong sign of the kinetic term, such as [[Pauli–Villars regularization\|Pauli–Villars ghosts]]—whose existence allows [[Negative probability\|the probabilities to be negative]] thus violating [[Unitarity (physics)\|unitarity]].

	~~== Changing the symmetry ==~~
	Ghost particles could obtain the symmetry or break it in gauge fields. The "good ghost" particles actually obtain the symmetry by unchanging the "gauge fixing lagrangian" in a gauge transformation, while bad ghost particles break the symmetry by bringing in the non-abelian G-matrix which does change the symmetry, and this was the main reason to ~~introduce the Gauge covariant~~ and ~~contravariant derivatives~~.

	~~==References==~~
	~~{{reflist}}~~
	* L.~~D. Faddeev and V.N~~. ~~Popov, Feynman Diagrams for the Yang-Mills Field, Phys~~. ~~Lett~~. ~~B25 (1967) 29.~~

	~~==External links==~~
	* [http://~~www.scholarpedia.org/article/Faddeev-Popov_ghosts Scholarpedia]~~
	* {{cite web\|last=Copeland\|first=Ed\|title=Ghost Particles\|url=http://www.~~sixtysymbols~~.com/~~videos/ghost_particles.htm\|work=Sixty Symbols\|publisher=[[Brady Haran]] for the [[University of Nottingham]]\|coauthors=Padilla, Antonio (Tony)}}~~

	~~{{particles}}~~

	~~{{DEFAULTSORT:Faddeev-Popov ghost}}~~
	~~[[Category:Quantum field theory]]~~
	~~[[Category:Quantum chromodynamics]~~]

en>Wikispaghetti: lay-out: removed unnecessary return

2014-01-11T23:20:32Z

lay-out: removed unnecessary return

New page

{{Quantum field theory|cTopic=Some models}}
In [[physics]], '''Faddeev–Popov ghosts''' (also called '''ghost fields''') are additional [[field (physics)|fields]] which are introduced into [[gauge theories|gauge]] [[quantum field theory|quantum field theories]] to maintain the consistency of the [[path integral formulation]]. They are named after [[Ludvig Faddeev]] and [[Victor Popov]].<ref>W. F. Chen. [http://arxiv.org/abs/0803.1340v2 Quantum Field Theory and Differential Geometry]</ref>

There is also a more general meaning of the word "'''ghost'''" in [[theoretical physics]], which is discussed below (see ''[[#General ghosts in theoretical physics|general ghosts in theoretical physics]]'').

==Overcounting in Feynman path integrals==
The necessity for Faddeev–Popov ghosts follows from the requirement that in the [[path integral formulation]], [[quantum field theory|quantum field theories]] should yield unambiguous, non-singular solutions. This is not possible when a [[gauge symmetry]] is present since there is no procedure for selecting any one solution from a range of physically equivalent solutions, all related by a gauge transformation. The problem stems from the path integrals overcounting field configurations related by gauge symmetries, since those correspond to the same physical state; the [[measure (mathematics)|measure]] of the path integrals contains a factor which does not allow obtaining various results directly from the original [[Action (physics)|action]] using the regular methods (e.g., [[Feynman diagram]]s). It is possible, however, to modify the action, such that the regular methods will be applicable by adding some additional fields, which break the gauge symmetry, which are called the ''ghost fields''. This technique is called the "Faddeev–Popov procedure" (see also [[BRST quantization]]). The ghost fields are a computational tool in that they do not correspond to any real particles in external states: they ''only'' appear as [[virtual particle]]s in Feynman diagrams – or as the ''absence'' of some gauge configurations. However they are necessary to preserve [[unitarity (physics)|unitarity]].

The exact form or formulation of ghosts is dependent on the particular [[Gauge fixing|gauge]] chosen, although the same physical results are obtained with all the gauges. The [[Gauge fixing|Feynman-'t Hooft gauge]] is usually the simplest gauge for this purpose, and is assumed for the rest of this article.

==Spin-statistics relation violated==
The Faddeev–Popov ghosts violate the [[spin-statistics relation]], which is another reason why they are often regarded as "non-physical" particles.

For example, in [[Yang–Mills theory|Yang–Mills theories]] (such as [[quantum chromodynamics]]) the ghosts are [[complex number|complex]] [[scalar field theory|scalar fields]] ([[spin (physics)|spin]] 0), but they [[anticommutativity|anti-commute]] (like [[fermions]]).

In general, [[anticommutativity|anti-commuting]] ghosts are associated with [[fermion]]ic symmetries, while [[commutativity|commuting]] ghosts are associated with [[boson]]ic symmetries.

==Gauge fields and associated ghost fields==
Every gauge field has an associated ghost, and where the gauge field acquires a mass via the [[Higgs mechanism]], the associated ghost field acquires the same mass (in the Feynman-'t Hooft gauge only, not true for other gauges).

==Appearance in Feynman diagrams==
In [[Feynman diagram]]s the ghosts appear as closed loops wholly composed of 3-vertices, attached to the rest of the diagram via a gauge particle at each 3-vertex. Their contribution to the [[S matrix|S-matrix]] is exactly cancelled (in the [[Feynman gauge|Feynman-'t Hooft gauge]]) by a contribution from a similar loop of gauge particles with only 3-vertex couplings or gauge attachments to the rest of the diagram. (A loop of gauge particles not wholly composed of 3-vertex couplings is not cancelled by ghosts.) The opposite sign of the contribution of the ghost and gauge loops is due to them having opposite fermionic/bosonic natures. (Closed fermion loops have an extra −1 associated with them; bosonic loops don't.)

==Ghost field Lagrangian==
The Lagrangian for the ghost fields <math>c^a(x)\,</math> in [[Yang–Mills theory|Yang–Mills theories]] (where <math>a</math> is an index in the adjoint representation of the [[gauge group]]) is given by
:<math>\mathcal{L}_\mathrm{ghost} = \partial_\mu \overline{c}^a\partial^\mu c^a + g f^{abc}(\partial^\mu\overline{c}^a) A_\mu^b c^c. </math>
The first term is a kinetic term like for regular complex scalar fields, and the second term describes the interaction with the [[gauge field]]s. Note that in ''abelian'' gauge theories (such as [[quantum electrodynamics]]) the ghosts do not have any effect since <math>f^{abc} = 0</math> and, consequently, the ghost particles do not interact with the gauge fields.

==General ghosts in theoretical physics==
The Faddeev–Popov ghosts are sometimes referred to as "good ghosts". The "bad ghosts" represent another, more general meaning of the word "ghost" in [[theoretical physics]]: states of negative norm—or fields with the wrong sign of the kinetic term, such as [[Pauli–Villars regularization|Pauli–Villars ghosts]]—whose existence allows [[Negative probability|the probabilities to be negative]] thus violating [[Unitarity (physics)|unitarity]].

== Changing the symmetry ==
Ghost particles could obtain the symmetry or break it in gauge fields. The "good ghost" particles actually obtain the symmetry by unchanging the "gauge fixing lagrangian" in a gauge transformation, while bad ghost particles break the symmetry by bringing in the non-abelian G-matrix which does change the symmetry, and this was the main reason to introduce the Gauge covariant and contravariant derivatives.

==References==
{{reflist}}
* L.D. Faddeev and V.N. Popov, Feynman Diagrams for the Yang-Mills Field, Phys. Lett. B25 (1967) 29.

==External links==
* [http://www.scholarpedia.org/article/Faddeev-Popov_ghosts Scholarpedia]
* {{cite web|last=Copeland|first=Ed|title=Ghost Particles|url=http://www.sixtysymbols.com/videos/ghost_particles.htm|work=Sixty Symbols|publisher=[[Brady Haran]] for the [[University of Nottingham]]|coauthors=Padilla, Antonio (Tony)}}

{{particles}}

{{DEFAULTSORT:Faddeev-Popov ghost}}
[[Category:Quantum field theory]]
[[Category:Quantum chromodynamics]]