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Register a new userMa-xion: Majoron as QCD axion in a radiative seesaw model
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The smallness of neutrino mass, the strong CP problem, and the existence of dark matter are explained in an economical way. The neutrino mass is generated by the colored version of a radiative seesaw mechanism by using color adjoint mediators. The Majorana mass term of the adjoint fermion, which carries lepton number U(1)_L, is induced by its spontaneous breaking, resulting in a Majoron which doubles as the QCD (quantum chromodynamics) axion, thereby solving the strong CP problem. The breaking of U(1)_L sets simultaneously the seesaw scale for neutrino mass and the Peccei-Quinn breaking scale. This axion is a good candidate for dark matter as usually assumed.
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The generation of neutrino masses by inverse seesaw mechanisms has advantages over other seesaw models since the potential new physics can be produced at the TeV scale. We propose a model that generates the inverse seesaw mechanism via spontaneous breaking of the lepton number, by extending the Standard Model with two scalar singlets and two fermion singlets both charged under lepton number. The model gives rise to a massless Majoron and a massive pseudoscalar which we dub as massive Majoron, which corresponds to the Nambu-Goldstone boson of the breaking of lepton number. If the massive Majoron is stable in cosmological time, it might play the role of a suitable Dark Matter candidate. In this scenario, we examine the model with a massive Majoron in the keV range. In this regime, its decay mode to neutrinos is sensitive to the ratio between the vevs of the new scalars ($omega$), and it vanishes when $ omega simeq sqrt{2/3}$, which is valid within a large region in the parameter space. On the other hand, the cosmological lifetime for the Dark Matter candidate places constraints on its mass via scalar decays. In addition, simple mechanisms that explain the Dark Matter relic abundance within this context and plausible modifications to the proposed setup are briefly discussed.
We propose an attractive model that excess of electron recoil events around 1-5 keV reported by the XENON1T collaboration nicely links to the tiny neutrino masses based on a radiative seesaw scenario. Our dark matter(DM) is an isospin singlet inert boson that plays an role in generating non-vanishing neutrino mass at one-loop level, and this DM inelastically interacts with a pair of electrons at one-loop level that is required to explain the XENON1T anomaly. It is also demanded that the mass difference between an excited DM and DM has to be of the order keV. Interestingly, the small mass difference $sim$keV is proportional to the neutrino masses. It suggests that we have double suppressions through the tiny mass difference and the one-loop effect. Then, we show some benchmark points to explain the XENON1T anomaly, satisfying all the constraints such as the event ratio of electrons of XENON1T, a long lived particle be longer than the age of Universe, and relic density in addition to the neutrino oscillation data and lepton flavor violations(LFVs).
We investigate a possibility for explaining the recently announced 750,GeV diphoton excess by the ATLAS and the CMS experiments at the CERN LHC in a model with multiple doubly charged particles, which was originally suggested for explaining tiny neutrino masses through a three-loop effect in a natural way. The enhanced radiatively generated effective coupling of a new singlet scalar $S$ with diphoton with multiple charged particles in the loop enlarges the production rate of $S$ in $ppto S+X$ via photon fusion process and also the decay width $Gamma(Sto gammagamma)$ even without assuming a tree level production mechanism. We provide detailed analysis on the cases with or without allowing the mixing between $S$ and the standard model Higgs doublet.
The lepton flavour violating charged lepton decays mu to e + gamma and thermal leptogenesis are analysed in the minimal supersymmetric standard model with see-saw mechanism of neutrino mass generation and soft supersymmetry breaking terms with universal boundary conditions. Hierarchical spectrum of heavy Majorana neutrino masses, M_1 << M_2 << M_3, is considered. In this scenario, the requirement of successful thermal leptogenesis implies a lower bound on M_1. For the natural GUT values of the heaviest right-handed Majorana neutrino mass, M_3 > 5 times 10^{13} GeV, and supersymmetry particle masses in the few times 100 GeV range, the predicted mu to e + gamma decay rate exceeds by few order of magnitude the experimental upper limit. This problem is avoided if the matrix of neutrino Yukawa couplings has a specific structure. The latter leads to a correlation between the baryon asymmetry of the Universe predicted by leptogenesis, BR(mu to e + gamma) and the effective Majorana mass in neutrinoless double beta decay.
The singlet majoron model of seesaw neutrino mass is appended by one dark Majorana fermion singlet $chi$ with $L=2$ and one dark complex scalar singlet $zeta$ with $L=1$. This simple setup allows $chi$ to obtain a small radiative mass anchored by the same heavy right-handed neutrinos, whereas the one-loop decay of the standard-model Higgs boson to $chi chi + bar{chi} bar{chi}$ provides the freeze-in mechanism for $chi$ to be the light dark matter of the Universe.
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