 Cubic anomaly coefficient

For a representation $R$ of $SU(N)$ with $N\ge 3$, choose the Hermitian quantum generator convention and normalize the cubic anomaly coefficient byHere the anticommutator symmetrizes the last two generators; cyclic property of the trace makes the whole tensor symmetric. This coefficient multiplies the local four-dimensional gauge anomaly from a chiral fermion in $R$. It adds under direct sums.

The conjugate representation has generators $-(T^a{)}^T$, so transposition and the three minus signs give $A(\overline{R})=-A(R)$. Hence a real representation or pseudoreal representation has zero cubic anomaly coefficient. For $SU(3)$, the two-index antisymmetric representation is the conjugate triplet and has coefficient $-1$. For $SU(2)$ the symmetric cubic invariant itself vanishes, so normalization to a nonzero fundamental cubic coefficient is unavailable; this statement concerns the local cubic anomaly and does not settle global anomalies.^[ref]