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Register a new userConstraining a general U(1)$^prime$ inverse seesaw model from vacuum stability, dark matter and collider
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We consider a class of gauged $U(1)$ extensions of the Standard Model (SM), where the light neutrino masses are generated by an inverse seesaw mechanism. In addition to the three right handed neutrinos, we add three singlet fermions and demand an extra $Z_2$ symmetry under which, the third generations of both of the neutral fermions are odd, which in turn gives us a stable dark matter candidate. We express the $U(1)$ charges of all the fermions in terms of the U(1) charges of the standard model Higgs and the new complex scalar. We study the bounds on the parameters of the model from vacuum stability, perturbative unitarity, dark matter relic density and direct detection constraints. We also obtain the collider constraints on the $Z$ mass and the $U(1)$ gauge coupling. Finally we compare all the bounds on the $Z$ mass versus the $U(1)$ gauge coupling plane.
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We study a class of general U$(1)^prime$ models to explain the observed dark matter relic abundance and light neutrino masses. The model contains three right handed neutrinos and three gauge singlet Majorana fermions to generate the light neutrino mass via the inverse seesaw mechanism. We assign one pair of degenerate sterile neutrinos to be the dark matter candidate whose relic density is generated by the freeze-in mechanism. We consider different regimes of the masses of the dark matter particle and the ${Z^prime}$ gauge boson. The production of the dark matter can occur at different reheating temperatures in various scenarios depending on the masses of the ${Z^prime}$ boson and the dark matter candidate. We also note that if the mass of the sterile neutrino dark matter is $gtrsim 1 rm{MeV}$ and if the $Z^prime$ is heavier than the dark matter, the decay of the dark matter candidate into positrons can explain the long standing puzzle of the galactic $511rm{keV}$ line in the Milky Way center observed by the INTEGRAL satellite. We constrain the model parameters from the dark matter analysis, vacuum stability and the collider searches of heavy ${Z^prime}$ at the LHC. For the case with light $Z^prime$, we also compare how far the parameter space allowed from dark matter relic density can be probed by the future lifetime frontier experiments SHiP and FASERs in the special case of $U(1)_{B-L}$ model.
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 analyse supersymmetric models augmented by an extra $U(1)$ gauge group. To avoid anomalies in these models without introducing exotics, we allow for family-dependent $U(1)^prime$ charges, and choose a simple form for these, dependent on one $U(1)^prime$ charge parameter only. With this choice, $Z^prime$ decays into di-taus but not di-leptons, weakening considerably the constraints on its mass. In the supersymmetric sector, the effect is to lower the singlino mass, allowing it to be the dark matter candidate. We investigate the dark matter constraints and collider implications of such models, with mostly singlino, or mostly higgsinos, or a mixture of the two as lightest supersymmetric particles. In these scenarios, $Z^prime$ decays significantly into chargino or neutralino pairs, and thus indirectly into final state leptons. We devise benchmarks which, with adequate cuts, can yield signals visible at the high-luminosity LHC.
In a novel standard model extension it has been suggested that, even in the absence of right-handed neutrinos and type-I seesaw, purely triplet leptogenesis leading to baryon asymmetry of the universe can be realised by two heavy Higgs triplets which also provide type-II seesaw ansatz for neutrino masses. In this work we discuss this model for hierarchical neutrino masses in concordance with recently determined cosmologocal bounds and oscillation data including $theta_{23}$ in the second octant and large Dirac CP phases. We also address the issues on dark matter and vacuum stability of the scalar potential in a minimal extension of this model. We find that for both normal and inverted orderings the model fits the oscillation data with the sum of the three neutrino masses consistent with cosmological bounds determined from Planck satellite data. In addition using this model ansatz for CP-asymmetry and solutions of Boltzmann equations, we also show how successful prediction of baryon asymmetry emerges in the cases of both unflavoured and two-flavoured leptogeneses. With additional $Z_2$ discrete symmetry, a minimal extension of this model is shown to be capable of predicting a scalar singlet WIMP dark matter in agreement with direct and indirect observations. Whereas in the original model, the renormalization group running of the scalar potential renders it negatve leading to vacuum instability, the presence of the dark matter in the minimally extended model ensures stability. Although the combined constraints due to relic density and direct detection cross section allow this scalar singlet dark matter mass to be $m_{xi}=750$ GeV, the additional vacuum stability constraint pushes this limiting value to $m_{xi}=1.3$ TeV which is verifiable by ongoing experiments. We also dicuss constraint on the model parameters for the radiative stability of the standard Higgs mass.
We analyze the prospects for light neutralino dark matter in the minimal supersymmetric model extended by a $U(1)$ gauge group. We allow the neutralino to be an arbitrary admixture of singlet and doublet higgsinos, as well as of the three gauginos, and we require agreement with the data from the direct and indirect dark matter detection experiments, while maintaining consistency of the model with the relic density and with the recent Higgs data from the LHC. The constraints have implications for the structure of the lightest neutralino as a dark matter candidate, indicating that it is largely singlino, and its mass can be as light as $sim 20 $ GeV.
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