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| {{Unreferenced|date=December 2009}}
| | Hi there. Allow me start by introducing the author, her title is Myrtle Cleary. North Dakota is her birth place but she will have to transfer one working day or an additional. For many years I've been working as a payroll clerk. To collect cash is what his family and him appreciate.<br><br>Here is my weblog: [http://www.ddaybeauty.com/node/14766 at home std testing] |
| {{expert|date=August 2012}}
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| In [[mathematical physics]], in particular in [[effective field theory]], a '''form factor''' is a [[function (mathematics)|function]] that gives the properties of a certain [[Fundamental interaction|particle interaction]] without including all of the underlying [[physics]]. It is measured experimentally when a theoretical calculation is unavailable or too difficult, see [[experimental particle physics]].
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| ==Photon-nucleon example==
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| For example, at low energies the interaction of a [[photon]] with a [[nucleon]] is a very complicated calculation involving interactions between the photon and a sea of [[quark]]s and [[gluon]]s, and often the calculation cannot be done. Often in this context, form factors are also called "structure functions", since they can be used to describe the structure of the nucleon. | |
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| However the general form of the interaction is known,
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| : <math>\varepsilon_\mu \bar{N}\left(\alpha(q^2) \gamma^\mu + \beta(q^2) q^\mu + \kappa(q^2) \sigma^{\mu \nu} q_\nu \right)N \, </math>
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| where <math>q^\mu</math> represents the photon [[momentum]] (equal to ''E''/''c'', where ''E'' is the energy of the photon). The three functions: <math> \alpha, \beta , \kappa </math> are the '''form factors''' for this interaction, they can be measured experimentally, and then the three effective vertices can be used to perform calculations that would otherwise be too difficult.
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| ==See also==
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| *[[Quantum field theory]]
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| *[[Standard model]]
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| *[[Quantum mechanics]]
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| *[[Special relativity]]
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| {{DEFAULTSORT:Form Factor (Quantum Field Theory)}}
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| [[Category:Quantum field theory]]
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Latest revision as of 14:02, 11 January 2015
Hi there. Allow me start by introducing the author, her title is Myrtle Cleary. North Dakota is her birth place but she will have to transfer one working day or an additional. For many years I've been working as a payroll clerk. To collect cash is what his family and him appreciate.
Here is my weblog: at home std testing