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Register a new userHierarchical Quark and Lepton Masses with Sequential U(1) Gauge Symmetry
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Ernest Ma
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Instead of right-handed neutrino singlets, the standard model is extended to include lepton triplets $(Sigma^+, Sigma^0, Sigma^-)$. Each quark and lepton family may now transform under an anomaly-free $U(1)_X$ gauge symmetry, known already for many years. A new sequential application is presented, using just the one Higgs doublet of the standard model, together with two $U(1)_X$ Higgs singlets. The resulting structure has hierarchical quark and lepton masses, as well as a viable seesaw neutrino mass matrix.
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We revisit our previous model proposed in Ref. cite{Okada:2013iba}, in which lepton masses except the tauon mass are generated at the one-loop level in a TeV scale physics. Although in the previous work, rather large Yukawa couplings constants; i.e., greater than about 3, are required to reproduce the muon mass, we do not need to introduce such a large but ${cal O}$(1) couplings. In our model, masses for neutrinos (charged-leptons) are generated by a dimension five effective operator with two isospin triplet (singlet and doublet) scalar fields. Thus, the mass hierarchy between neutrinos and charged-leptons can be naturally described by the difference in the number of vacuum expectation values (VEVs) of the triplet fields which must be much smaller than the VEV of the doublet field due to the constraint from the electroweak rho parameter. Furthermore, the discrepancy in the measured muon anomalous magnetic moment ($g-2$) from the prediction in the standard model are explained by one-loop contributions from vector-like extra charged-leptons which are necessary to obtain the radiative generation of the lepton masses. We study the decay property of the extra leptons by taking into account the masses of muon, neutrinos, muon $g-2$ and dark matter physics. We find that the extra leptons can mainly decay into the mono-muon, dark matter with or without $Z$ bosons in the favored parameter regions.
General Two Higgs Doublet Models (2HDM) are popular Standard Model extensions but feature flavor changing interactions and lack neutrino masses. We discuss a 2HDM where neutrino masses are generated via type I seesaw and propose an extension where neutrino masses are generated via a type II seesaw mechanism with flavor changing interactions being absent via the presence of a U(1) gauge symmetry. After considering a variety of bounds such as those rising from collider and electroweak precision we show that our proposal stands as a UV complete 2HDM with a dark photon where neutrino masses and flavor changing interactions are addressed. A possible dark matter realization is also discussed.
We show that in a large class of models based on anomalous U(1) symmetry which addresses the fermion mass hierarchy problem, leptonic flavor changing processes are induced that are in the experimentally interesting range. The flavor violation occurs through the renormalization group evolution of the soft SUSY breaking parameters between the string scale and the U(1)_A breaking scale. We derive general expressions for the evolution of these parameters in the presence of higher dimensional operators. Several sources for the flavor violation are identified: flavor-dependent contributions to the soft masses from the U(1)_A gaugino, scalar mass corrections proportional to the trace of U(1)_A charge, non-proportional A-terms from vertex corrections, and the U(1)_A D-term. Quantitative estimates for the decays mu -> e gamma and tau -> mu gamma are presented in supergravity models which accommodate the relic abundance of neutralino dark matter.
We propose a radiative lepton model, in which the charged lepton masses are generated at one-loop level, and the neutrino masses are induced at two-loop level. On the other hand, tau mass is derived at tree level since it is too heavy to generate radiatively. Then we discuss muon anomalous magnetic moment together with the constraint of lepton flavor violation. A large muon magnetic moment is derived due to the vector like charged fermions which are newly added to the standard model. In addition, considering a scalar dark matter in our model, a strong gamma-ray signal is produced by dark matter annihilation via internal bremsstrahlung. We can also obtain the effective neutrino number by the dark radiation of the Goldstone boson coming from the imposed global $U(1)$ symmetry.
We propose a model with the left-handed and right-handed continuous Abelian gauge symmetry; $U(1)_Ltimes U(1)_R$. Then three right-handed neutrinos are naturally required to achieve $U(1)_R$ anomaly cancellations, while several mirror fermions are also needed to do $U(1)_L$ anomaly cancellations. Then we formulate the model, and discuss its testability of the new gauge interactions at collider physics such as the large hadron collider (LHC) and the international linear collider (ILC). In particular, we can investigate chiral structure of the interactions by the analysis of forward-backward asymmetry based on polarized beam at the ILC.
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