gauge invariance - help asap? | Page 1 | The Physics and Mathematics Guild | Guild Forums

xsparkledovex

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Posted: Wed May 23, 2007 2:07 am

How do I prove that something's gauge invariant? local and global symmetry right? I just dont know how to apply it confused

like ...
hopefully this link works
http://www.tcd.ie/Local/Exam_Papers/2006/XM/XMA4441.pdf
in question 1
and http://www.tcd.ie/Local/Exam_Papers/2005/XM/XMA4441.pdf
like in the last link where phi -> phi + da do i just stick phi + da into the L equation and see what happens? confused what do I want to happen?

(anyone knows anything about gamma matrices stuff as well, that'd be appreciated)

Posted: Wed May 23, 2007 5:20 pm

Normally you want the Lagranigian density to remain the same if you introduce a local and global gauge.

I can be more help with the gamma matrices. Remember whether two adjacent matrices commute or anticommute. Aim to get two matrices next to each other so that you can cancel them into the identity matrix.

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xsparkledovex

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Posted: Tue May 29, 2007 2:36 am

A Lost Iguana

Normally you want the Lagranigian density to remain the same if you introduce a local and global gauge.

I can be more help with the gamma matrices. Remember whether two adjacent matrices commute or anticommute. Aim to get two matrices next to each other so that you can cancel them into the identity matrix.

I tried reading my notes instead of panicing and realised that gamma matrices are really easy
so that's one question I can do
stupid exam is 8 questions do 6 stare

ok I want it the same, thanks... we did this stuff way back in november so I forget

Posted: Wed May 30, 2007 1:36 am

Don't forget to exploit the cyclic-symmetry of traces if you need to show a trace property [these are essential when calculating matrix elements for Feynman diagrams].

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xsparkledovex

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Posted: Wed May 30, 2007 11:33 pm

A Lost Iguana

Don't forget to exploit the cyclic-symmetry of traces if you need to show a trace property [these are essential when calculating matrix elements for Feynman diagrams].

3nodding

do you know, perchance, what the answer to q3 is on those papers?
as in, why does the lorentz trans coulomb gauge thingy transform that way, and how do you find lambda?

Posted: Fri Jun 01, 2007 9:35 am

well, i had the answer
since he asked it every year
but this year he didnt
git
stare

xsparkledovex

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