= Proton-lifetime bound on a product of R-parity-violating couplings
{title2=$|\lambda\prime\lambda\prime\prime|<M^2(c_h\tau_{\min}m_p^5)^{-1/2}$}
Exchanging a down-type <squark> of mass $M$ between $LQD$ and $UDD$ vertices produces a dimension-six <effective operator> with coefficient $C\sim\lambda'\lambda''/M^2$. <Dimensional analysis> then gives a <proton decay> width $\Gamma_p=c_h|\lambda'\lambda''|^2m_p^5/M^4$, with a dimensionless factor $c_h$ containing hadronic matrix elements and phase space. A lifetime bound $\tau_p>\tau_{\min}$ implies $|\lambda'\lambda''|<M^2/\sqrt{c_h\tau_{\min}m_p^5}$. The bound is on the relevant flavour product and depends on the exchanged mass; <dimensional analysis> alone does not determine $c_h$.
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