Building Momentum Kernel from Shapovalov Form

These notes are an extended version of the talks given by the authors at the XIV International Workshop on Lie Theory and Its Applications in Physics, Sofia, Bulgaria, 20-26 June 2021. The concise version published in the proceedings of the workshop contains additional discussions for the $q$-deformed scenario: \noindent\href{https://link.springer.com/chapter/10.1007/978-981-19-4751-3_23}{https://link.springer.com/chapter/10.1007/978-981-19-4751-3\_23}. In these notes we identify KLT kernel with the Shapovalov form on Verma module with its highest/lowest weight given by the reference momentum and rest of the momenta as roots. We then take a step forward and show how the Feynman diagrams emerge naturally as the Shapovalov duals of the Verma module basis vectors. We show such algebraic construct offers a compact expression for the BCJ numerators. Explicit examples are shown for the nonlinear sigma model and the HEFT pre-numerators.