Three-body weak-decay mass correction
= Three-body weak-decay mass correction
{title2=$f(r)=1-8r+8r^3-r^4-12r^2\ln r$}
For a tree-level left-handed three-body decay with one massive final <fermion> and two massless ones, the integrated width relative to the all-massless result includes $f(r)=1-8r+8r^3-r^4-12r^2\ln r$, where $r$ is the squared final-to-parent <mass> ratio. It satisfies $f(0)=1$ and $f(1)=0$. It is not a universal factor for channels with several massive daughters.