Flipped SU(5)

The Flipped SU(5) model is a Grand Unified Theory (GUT) theory first contemplated by Stephen Barr in 1982, and by Dimitri Nanopoulos and others in 1984. Ignatios Antoniadis, John Ellis, John Hagelin, and Nanopoulos developed the supersymmetric flipped SU(5), derived from the deeper-level superstring.

Current efforts to explain the theoretical underpinnings for observed neutrino masses are being developed in the context of supersymmetric flipped $SU(5)$ .

Flipped $SU(5)$ is not a fully unified model, because the $U(1) Y$ factor of the SM gauge group is within the $U(1)$ factor of the GUT group. The addition of states below Mx in this model, while solving certain threshold correction issues in string theory, makes the model merely descriptive, rather than predictive.

The flipped $SU(5)$ model states that the gauge group is:

Fermions form three families, each consisting of the representations

This assignment includes three right-handed neutrinos, which have never been observed, but are often postulated to explain the lightness of the observed neutrinos and neutrino oscillations. There is also a $101$ and/or $10 -1$ called the Higgs fields which acquire a VEV, yielding the spontaneous symmetry breaking

The $SU(5)$ representations transform under this subgroup as the reducible representation as follows:

The name "flipped" $SU(5)$ arose in comparison to the "standard" $SU(5)$ Georgi–Glashow model, in which $u c$ and $d c$ quark are respectively assigned to the $10$ and $5$ representation. In comparison with the standard $SU(5)$ , the flipped $SU(5)$ can accomplish the spontaneous symmetry breaking using Higgs fields of dimension 10, while the standard $SU(5)$ requires both a 5- and 45-dimensional Higgs.

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