= Vector decay into identical spin-zero mesons
A spin-one parent cannot decay into two identical spin-zero particles in the same internal state while preserving rotational <symmetry> and Bose exchange <symmetry>. Their final total <angular momentum> is orbital $L=1$, which is antisymmetric under interchange. Bose <symmetry> requires even $L$ instead. An energetically allowed decay with matching <parity> can therefore remain forbidden independently of the interaction's coupling strength.
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