Dirac gauginos and unification in F-theory

TL;DR

This paper explores how Dirac gaugino masses can be realized in F-theory models, examining their impact on gauge unification, the necessary geometric conditions, and the role of R-symmetry for viable supersymmetric models.

Contribution

It demonstrates the realization of Dirac gauginos in F-theory, analyzes their effects on gauge unification, and discusses geometric and flux conditions for consistent model building.

Findings

Viable gauge unification at the Planck scale with extra leptons.

Conditions for geometry and flux in F-theory models with Dirac gauginos.

A model with R-symmetry and adjoint multiplets compatible with SU(5) breaking.

Abstract

Supersymmetric models in which the gauginos acquire Dirac masses, rather than Majorana masses, offer an appealing alternative to the minimal supersymmetric standard model, especially in the light of the bounds set on superpartner masses by the 2011 LHC data. Dirac gauginos require the presence of chiral multiplets in the adjoint representation of the gauge group, and the realisation of such scenarios in F-theory is the subject of this paper. The chiral adjoints drastically alter the usual picture of gauge coupling unification, but this is disturbed anyway in F-theory models with non-trivial hypercharge flux. The interplay between these two factors is explored, and it is found for example that viable F-theory unification can be achieved at around the reduced Planck scale, if there is an extra vector-like pair of singlet leptons with TeV-scale mass. I then discuss the conditions which must be satisfied by the geometry and hypercharge flux of an F-theory model with Dirac gauginos. One nice possibility is for the visible sector to be localised on a K3 surface, and this is discussed in some detail. Finally, I describe how to achieve an unbroken discrete R-symmetry in such compactifications, which is an important ingredient in many models with Dirac gauginos, and write down a simple example which has adjoint chiral multiplets, an appropriate R-symmetry, and allows for viable breaking of SU(5) by hypercharge flux.