= Effective operator
{title2=$C_i\mathcal O_i/M^{\Delta_i-4}$}
An effective operator is a local interaction built from the retained fields in an <effective field theory>. Its <coefficient> records effects of heavier degrees of freedom, and allowed operators respect the relevant <symmetries>. In four dimensions an operator of <mass dimension> $\Delta_i$ has the displayed coefficient for dimensionless $C_i$ and a heavy <mass> scale $M$. For example a dimension-six <proton-decay operator> has a coefficient proportional to $M^{-2}$.
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