= Irrelevant coupling
In classical <power counting in quantum field theory>, an <irrelevant coupling> multiplies a <local operator> whose <mass dimension> $\Delta$ exceeds the <spacetime dimension> $d$. Since the <action> is dimensionless in <natural units>, $[g]=d-\Delta<0$. The dimensionless interaction strength scales as
$$
\widetilde g(E)=gE^{\Delta-d}.
$$
For example, $\phi^6$ in four-dimensional <scalar field theory> has coefficient $g/\Lambda^2$, giving suppression $g(E/\Lambda)^2$ at low <energy>. This explains the usefulness of <effective field theory> below its cutoff. At an interacting <renormalization-group fixed point>, relevance is determined by the full <scaling dimension>, including quantum corrections. <Quantum Field Theory by David Tong>[Chapter 3 opening discussion, equations 3.202–3.205 and quantum-correction qualification]{ref}
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