Monday, January 18, 2016

differential geometry - Inconsistency between dA=d+Awedge and dA=d(..)+[A,..]?


I am confused by something basic stated in this https://physics.stackexchange.com/a/429947/42982 by @ACuriousMind and some fact I knew of. Here dA is covariant derivative.




  1. dAA=F --- @ACuriousMind says "The field strength is the covariant derivative of the gauge field."




  2. The Bianchi identity is dAF=0.








  • In the 1st case, we need to define



dA=d+A



So dAA=(d+A)A=dA+AA




  • In the 2nd case, we need to define



dA=d(..)+[A,..]



So we get a correct Bianchi identity which easily can be checked to be true dAF=dF+[A,F]=d(dA+AA)+[A,dA+AA]=0


However, eq (1) and (2) look different.


e.g. if we use eq(2) for "The field strength is the covariant derivative of the gauge field.", we get a wrong result


dAA=dA+[A,A]=dAF!!!!


e.g. if we use eq(1) for "Bianchi identity", we get the wrong result we get dAF=dF+AF0




my puzzle: How to resolve def (1) and (2)?


Could it be that for the p-form dAω=dω+,

where depends on the p of the p-form? How precisely?





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