Effects of the Variation of SUSY Breaking Scale on Yukawa and Gauge Couplings Unification

The present analysis addresses an interesting primary question on how do the gauge and Yukawa couplings unification scales vary with varying SUSY breaking scales m_s, assuming a single scale for all supersymmetric particles. It is observed that the gauge coupling unification scale increases with m_s whereas third-generation Yukawa couplings unification scale decreases with m_s. The rising of the unification scale and also the mass of the color triplet multiplets is necessary to increase the proton decay lifetime; the analysis is carried out with two-loop RGEs for the gauge and Yukawa couplings within the minimal supersymmetric SU(5) model, while ignoring for simplicity the threshold effects of the heavy particles, which could be as large as a few percentages