Consider two massless representations of the connected Poincare group $ISO\_0(1,3)$ with helicities $s$ and $t$. What is the decomposition of their tensor product into irreducibles?


Massless representations with helicity s are defined in [Wigner's classification](https://en.wikipedia.org/wiki/Wigner%27s_classification) of irreducible unitary representations of the connected Poincare group, the semidirect product $ISO\_0(1,3)$ of the connected Lorentz group $SO\_0(1,3)$ and the 4-dimensional translation group. 



tensor product of massless Poincare representations
I think the answer is given in the paper <https://aip.scitation.org/doi/10.1063/1.1703659> (Decomposition of Direct Products of Representations of the Inhomogeneous Lorentz Group, by J. S. Lomont).


