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| {{more references|date=December 2009}} | |||
| {{expert needed|1=Physics|date=August 2017|reason=The article needs wikilove. Global and ] articles needs wikihelp and don't have much activity. Merging might be a better idea. Subjects are notable}} | |||
| In physics, a '''global symmetry''' is a ] that holds at all points in the ] under consideration, as opposed to a ] which varies from point to point. | |||
| Global symmetries require ]s, but not ], in physics. | |||
| An example of a global symmetry is the action of the <math>U(1)=e^{i\theta}</math> (for <math>\theta</math> a constant – making it a global transformation) group on the Dirac Lagrangian: | |||
| ::<math>\mathcal{L}_D = \bar{\psi}\left(i\gamma^\mu \partial_\mu-m\right)\psi</math> | |||
| Under this transformation the fermionic field changes as <math>\psi\rightarrow e^{i\theta}\psi</math> and <math>\bar{\psi}\rightarrow e^{-i\theta}\bar{\psi}</math><ref>http://www.damtp.cam.ac.uk/user/tong/qft.html</ref> and so: | |||
| ::<math>\mathcal{L}\rightarrow\bar{\mathcal{L}}=e^{-i\theta}\bar{\psi}\left(i\gamma^\mu \partial_\mu-m\right)e^{i\theta}\psi=e^{-i\theta}e^{i\theta}\bar{\psi}\left(i\gamma^\mu \partial_\mu-m\right)\psi=\mathcal{L}</math> | |||
| ==See also== | |||
| ⚫ | |||
| *] | |||
| *] | |||
| ==References== | |||
| <references /> | |||
| {{DEFAULTSORT:Global Symmetry}} | |||
| ] | |||
| ] | |||
| {{Physics-stub}} | |||
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