# $SU(5)$ model and flipped $SU(5)$ model

It seems that both $$SU(5)$$ model and flipped $$SU(5)$$ model are legal grand unified theories (GUT) for the standard model gauge group. In Wikipedia, it says that:

The flipped $$SU(5)$$ model has a gauge group breaking down $$(SU(5) × U(1)_ χ )/ Z_5 \to (SU(3) × SU(2) × U(1)_Y )/ Z_6$$ The flipped $$SU(5)$$ model representation branchings (very different from $$SU(5)$$ model): $$\bar{5}_{-3}\to (\bar{3},1)_{-\frac{2}{3}}\oplus (1,2)_{-\frac{1}{2}}$$ ($$u_c$$ and $$l$$) $$10_{1}\to (3,2)_{\frac{1}{6}}\oplus (\bar{3},1)_{\frac{1}{3}}\oplus (1,1)_0$$ ($$q$$, $$d_c$$ and $$ν_c$$) $$1_{5}\to (1,1)_1$$ ($$e_c$$)

My question is that:

• do we still have the $$B-L$$ or $$5(B-L)-2Y$$ global symmetry for the flipped $$SU(5)$$ model?

• Does the proton decay still happens in the flipped $$SU(5)$$ model?

• What are the pros and cons of $$SU(5)$$ model versus flipped $$SU(5)$$ model?