Representation of $SU(4)$

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I am trying to understand explicit description of spinors in dimension $6$. Now one can explain positive spinors in terms of the usual $4$-dimensional representation of $SU(4)\hookrightarrow GL(4).$ Now what's the corresponding representation for the negative spinors? Is this the only $4$-dimensional representation of $SU(4)$ up to isomorphism? What about the dual representation?

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We know that $\mathrm{SU}(4)\simeq \mathrm{Spin}(6)$. If we identify their root systems, the positive spinor representation of $\mathrm{Spin}(6)$ corresponds to the usual $4$-dimensional representation $V$ of $\mathrm{SU}(4)$, the natural $6$-dimensional representation of $\mathrm{Spin}(6)$ corresponds to the wedge product $\wedge^{2}V$ and the negative spinor representation corresponds to $\wedge^{3}V$. This can be verified easily by checking their highest weight. I think this is an explicit description of the negative spinor. The dual of the positive spinor representation is the negative spin representation.