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Register a new userOn the LHC signatures of $SU(5)times U(1)$ F-theory motivated models
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We study low energy implications of F-theory GUT models based on $SU(5)$ extended by a $U(1)$ symmetry which couples non-universally to the three families of quarks and leptons. This gauge group arises naturally from the maximal exceptional gauge symmetry of an elliptically fibred internal space, at a single point of enhancement, $E_8supset SU(5)times SU(5)supset SU(5)times U(1)^4$. Rank-one fermion mass textures and a tree-level top quark coupling are guaranteed by imposing a $Z_2$ monodromy group which identifies two abelian factors of the above breaking sequence. The $U(1)$ factor of the gauge symmetry is an anomaly free linear combination of the three remaining abelian symmetries left over by $Z_2$. Several classes of models are obtained, distinguished with respect to the $U(1)$ charges of the representations, and possible extra zero modes coming in vector-like representations. The predictions of these models are investigated and are compared with the LHC results and other related experiments. Particular cases interpreting the B-meson anomalies observed in LHCb and BaBar experiments are also discussed.
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Signatures of the $SO(5)times U(1)$ gauge-Higgs unification at LHC and future colliders are explored. The Kaluza-Klein (KK) mass spectra of $gamma, Z, Z_R$ and the Higgs self-couplings obey universality relations with the Aharonov-Bohm (AB) phase $theta_H$ in the fifth dimension. The current data at low energies and at LHC indicate $theta_H <0.2$. Couplings of quarks and leptons to KK gauge bosons are determined. Three neutral gauge bosons, the first KK modes $Z_R^{(1)}$, $Z^{(1)}$, and $gamma^{(1)}$, appear as $Z$ bosons in dilepton events at LHC. For $theta_H = 0.114$, the mass and decay width of $Z_R^{(1)}$, $Z^{(1)}$, and $gamma^{(1)}$ are (5.73TeV, 482GeV), (6.07TeV, 342GeV), and (6.08TeV, 886GeV), respectively. For $theta_H = 0.073$ their masses are 8.00TeV$sim$8.61TeV. An excess of events in the dilepton invariant mass should be observed in the $Z$ search at the upgraded LHC at 14TeV.
Motivated by experimental measurements indicating deviations from the Standard Model predictions we discuss F-theory inspired models, which, in addition to the three chiral generations contain a vector-like complete fermion family. The analysis takes place in the context of $SU(5)times U(1)$ GUT embedded in an $E_8$ covering group which is associated with the (highest) geometric singularity of the elliptic fibration. In this context, the $U(1)$ is a linear combination of four abelian factors subjected to appropriate anomaly cancellation conditions. Furthermore, we require universal $U(1)$ charges for the three chiral families and different ones for the corresponding fields of the vector-like representations. Under the aforementioned assumptions, we find 192 such models which can be classified into five distinct categories with respect to their specific GUT properties. We exhibit representative examples for each such class and construct the superpotential couplings and the fermion mass matrices. We explore the implications of the vector-like states in low energy phenomenology including the predictions regarding the B-meson anomalies. The r^ole of R-parity violating terms appearing in some particular models of the above construction is also discussed.
We explore the low energy phenomenology of an F-theory based SU(5) model which, in addition to the known quarks and leptons, contains Standard Model singlets, and vector-like color triplets and SU(2) doublets. Depending on their masses and couplings, some of these new particles may be observed at the LHC and future colliders. We discuss the restrictions by CKM constraints on their mixing with the ordinary down quarks of the three chiral familes. The model is consistent with gauge coupling unification at the usual supersymmetric GUT scale, dimension five proton decay is adequately suppressed, while dimension-six decay mediated by the superheavy gauge bosons is enhanced by a factor of 5-7. The third generation charged fermion Yukawa couplings yield the corresponding low-energy masses in reasonable agreement with observations. The hierarchical nature of the masses of lighter generations is accounted for via non-renormalisable interactions, with the perturbative vacuum expectation values of the SM singlet fields playing an essential role.
$SO(5) times U(1) times SU(3)$ gauge-Higgs unification model inspired by $SO(11)$ gauge-Higgs grand unification is constructed in the Randall-Sundrum warped space. The 4D Higgs boson is identified with the Aharonov-Bohm phase in the fifth dimension. Fermion multiplets are introduced in the bulk in the spinor, vector and singlet representations of $SO(5)$ such that they are implemented in the spinor and vector representations of $SO(11)$. The mass spectrum of quarks and leptons in three generations is reproduced except for the down quark mass. The small neutrino masses are explained by the gauge-Higgs seesaw mechanism which takes the same form as in the inverse seesaw mechanism in grand unified theories in four dimensions.
In F-theory GUTs, threshold corrections from Kaluza-Klein massive modes arising from gauge and matter multiplets play an important role in the determination of the weak mixing angle and the strong gauge coupling of the effective low energy model. In this letter we further explore the induced modifications on the gauge couplings running and the GUT scale. In particular, we focus on the KK-contributions from matter curves and analyse the conditions on the chiral and Higgs matter spectrum which imply a GUT scale consistent with the minimal unification scenario. As an application, we present an explicit computation of these thresholds for matter fields residing on specific non-trivial Riemann surfaces.
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