Unification and Phenomenology of F-Theory GUTs with U(1)_PQ

TL;DR

The paper investigates SU(5) F-theory GUTs augmented by a $U(1)_{PQ}$ symmetry, where hypercharge flux induces non-GUT exotics that affect gauge unification. It develops a framework incorporating 1-loop MSSM running, two-loop effects, and high- and low-scale threshold corrections, parametrizing exotics with $(M,N,K,L)$ and treating exotics as gauge-mediation messengers to generate a non-universal but consistent sparticle spectrum. The authors quantify how exotics and KK thresholds distort unification, argue about the (often limited) potential for cancellations, and demonstrate that unification can be preserved with order-one finite threshold parameters for certain flux choices. They then explore LHC phenomenology in high-scale GMSB scenarios with non-GUT messengers, presenting benchmark points and scanning the parameter space to show that the resulting MSSM spectra can be compressed or stretched by up to a factor of about three, depending on hypercharge flux, with distinctive non-universal gaugino masses that could distinguish these models from mGMSB via precision kinematic edges.

Abstract

We undertake a phenomenological study of SU(5) F-theory GUT models with an additional U(1)_{PQ} symmetry. In such models, breaking SU(5) with hypercharge flux leads to the presence of non-GUT multiplets in the spectrum. We study the effect these have on the unification of gauge couplings, including two-loop running as well as low- and high-scale threshold corrections. We use the requirement of unification to constrain the size of thresholds from KK modes of SU(5) gauge and matter fields. Assuming the non-GUT multiplets play the role of messengers of gauge mediation leads to controlled non-universalities in the sparticle spectrum while maintaining grand unification, and we study the LHC phenomenology of this scenario. We find that the MSSM spectrum may become compressed or stretched out {by up to a factor of three} depending on the distribution of hypercharge flux. We present a set of benchmark points whose production cross-sections and decays we investigate, and argue that precision kinematic edge measurements will allow the LHC to distinguish between our model and mGMSB.

Figures (5)

• Figure 1: This figure shows the effective mass scale $m_{SUSY}$ for low threshold corrections defined in the text in the $M_{\rm Mess}$ and $\Lambda$ plane. We have chosen the fluxes to be $(2,-1,0,0)$ so that $N-L=-1$, the same as for the benchmark point and scans discussed in Section \ref{['sec:phenomenology']}.
• Figure 2: Plots of $\Delta^{finite}$ in a parameter scan of (a) $(K,L,M,N)= (0,-2,1,0)$ and (b) $(3,2,0,0)$ parameter spaces.
• Figure 3: Plots of $\delta^{finite}_{M_U}$ in a parameter scan of (a) $(K,L,M,N)= (0,-2,1,0)$ and (b) $(3,2,0,0)$ parameter spaces.
• Figure 4: The left-hand plot (a) shows the viable parameter range in the $\log_{10}(M_{\rm Mess})-\log_{10}(\Lambda)$ plane for the flux choice $(2, -1, 0, 0)$, i.e. the model $\hbox{NonUniv}_{L=-1}^{\rm{SmallFlux}}$. It is coloured according to the values of $\tan\beta$ obtained at each viable point. The right hand plot (b) shows the mass of the lightest Higgs boson $h^0$. The contour line in this case is the exclusion limit from LEP, $m_h > 114.4$ GeV.
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