Massless p-form gauge field
= Massless p-form gauge field
{title2=$n_p(D)=\binom{D-2}{p}$}
A massless Abelian $p$-form in $D$-dimensional flat spacetime transforms on shell as an antisymmetric rank-$p$ tensor of the rotational <little group> $SO(D-2)$. Its physical state count is $\binom{D-2}{p}$. A compatible real self-duality constraint halves this count. A four-dimensional three-form has no local propagating polarization.