Wednesday, September 9, 2015

conventions - Index of representation of SU(N) fundamental and adjoint


Im getting crazy trying to derive this simple expression.


Say fabc are structure constants of a Lie algebra of SU(N) with [Ta,Tb]=ifabcTc. Then chosing normalization such that



c,dfacdfbcd=Nδab


Show that for fundamental rep of SU(N): tr(TaTb)=12δab


And for adjoint rep: tr(TaTb)=Nδab


Let me know if you have any suggestions, all much appreciated.


EDIT: Adjoint representation case is simply a matter of definition (Taadj)bc=ifabc


tr(TaTb)=famnfbnm=famnfbmn=Nδab




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