Renormalization group evolution ofR-parity-violating Yukawa couplings

We study the evolution of $R$-parity-violating (RPV) couplings in the minimum supersymmetric standard model, between the electroweak and grand unification scales, assuming a family hierarchy for these coupling strengths. Particular attention is given to solutions where both the $R$-conserving and $R$-violating top-quark Yukawa couplings simultaneously approach infrared fixed points; these we analyze both algebraically and with numerical solutions of the evolution equations at the one-loop level. We identify constraints on these couplings at the GUT scale, arising from lower limits on the top-quark mass. We show that fixed points offer a new source of bounds on RPV couplings at the electroweak scale. We derive evolution equations for the CKM matrix, and show that RPV couplings affect the scaling of the unitarity triangle. The fixed-point behavior is compatible with all present experimental constraints. However, fixed-point values of RPV top-quark couplings would require the corresponding sleptons or squarks to have a mass $\gtrsim m_t$ to suppress strong new top-quark decays to sparticles.