Flipped SU(5) Predicts $\delta T\mathrm{/}T$

We discuss hybrid inflation in supersymmetric flipped SU(5) model such that the cosmic microwave anisotropy $\delta T\mathrm{/}T$ is essentially proportional to $(M /M_{P})^2$,where$M$denotesthesymmetrybreakingscaleand$M_{P}$($=2.4\times 10^{18}$GeV)isthereducedPlanckmass\mathrm{.}Themagnitudeof$M$determinedfrom$\delta T/T$ measurements can be consistent with the value inferred from the evolution of SU(3) and SU(2) gauge couplings. In other words, one could state that flipped SU(5) predicts (more precisely `postdicts’) $\delta T\mathrm{/}T$. The scalar spectral index $n_s=0.993\pm 0.007$, the scalar to tensor ratio satisfies $r\text{lapproxeq}{10}^{-6}$, while $dn_s/d{\rm ln}k \lapproxeq 4\times 10^{-4}$.