Thursday, July 27, 2017

lagrangian formalism - Variation of gamma and Christoffel


I am trying to experiment with Lagrangian densities and came across a term similar to γiΓjikAk

where the γ are the gamma matrices, Γ are the Christoffel Symbols and A are the field components.


In the variation of the term my question is somewhat twofold: is there any "nice" way to compute δδglmγa, knowing the relation {γi,γj}=2gijI?






Secondly, from what I have seen δΓijk=Γjklδgil+gilδΓjkl, commonly rewritten in a different form. The question Variation of the Christoffel symbols with respect to gμν does not seem to have a satisfactory answer for my purpose; it seems like the variation terms will stay in the field equation so it does not make sense to leave variations in the expression. Is it valid to naively assume that δδglmΓjik=Γjkl?





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