Search

In this paper, we consider the sterile neutrino portal dark matter with $Z_3$ symmetry. This model further extends the canonical type-I seesaw with a fermion singlet $\chi$ and a scalar singlet $\phi$. Under the $Z_3$ symmetry, the dark sector transforms as $\chi\to e^{i2\pi/3}\chi, \phi\to e^{i2\pi/3}\phi$, while the standard model particles and the sterile neutrino $N$ transform trivially. Besides the interactions as $y_{N} \phi \bar{\chi}N$ and $\lambda_{H\phi} (H^\dag H) (\phi^\dag \phi)$ allowed in the $Z_2$ symmetry, the $Z_3$ symmetry also introduces two new terms, i.e., $y_\chi \phi \overline{\chi^{c}} \chi$ and $\mu\phi^3/2$. These new interactions induce additional semi-annihilation processes as $\chi\chi\to N\chi$ and $\phi\phi\to h\phi$ for WIMP dark matter. We then perform a comprehensive analysis of the phenomenology of this $Z_3$ symmetric model. Viable parameter space is explored under the constraints from dark matter relic density, Higgs invisible decay, indirect and direct detection for both fermion and scalar dark matter. We find that the semi-annihilation channels $\chi\chi\to N\chi$ and $\phi\phi\to N\chi$ can lead to quite different phenomena from the $Z_2$ symmetric model, which provides a viable pathway to distinguish these two kinds of model., Comment: 23 pages, 10 figures

Provided the dark sector consisted of a dark scalar $\phi$ and a dark fermion $\chi$ under an exact $Z_2$ symmetry, the sterile neutrino $N$ can act as the messenger between the dark sector and standard model via the Yukawa coupling $\lambda_{ds} \bar{\chi}\phi N$. In this paper, we focus on the specific scenario $m_N>m_\phi+m_\chi$ with $\chi$ being a FIMP dark matter. The decay width of dark scalar $\phi$ is doubly suppressed by the smallness of Yukawa coupling $\lambda_{ds}$ and mixing angle $\theta$. The delayed decay $\phi\to\chi\nu$ will have a great impact on cosmological observables such as the Big Bang Nucleosynthesis, the Cosmic Microwave Background anisotropy power spectra, the effective number of relativistic neutrino species $N_{\rm eff}$ and the energetic neutrino flux. Meanwhile, the sterile neutrino can generate displaced vertex signature at colliders when $m_N, Comment: 18 pages,8 figures

In this paper, we propose the sterile neutrino portal dark matter in $ν$THDM. This model can naturally generate tiny neutrino mass with the neutrinophilic scalar doublet $Φ_ν$ and sterile neutrinos $N$ around TeV scale. Charged under a $Z_2$ symmetry, one Dirac fermion singlet $χ$ and one scalar singlet $ϕ$ are further introduced in the dark sector. The sterile neutrinos $N$ are the mediators between the DM and SM. Depending on the coupling strength, the DM can be either WIMP or FIMP. For the WIMP scenario, pair annihilation of DM into $NN$ is the key channel to satisfy various bounds, which could be tested at indirect detection experiments. For the FIMP scenario, besides the direct production of DM from freeze-in mechanism, contributions from late decay of NLSP is also important. When sterile neutrinos are heavier than the dark sector, NLSP is long-lived due to tiny mixing angle between sterile and light neutrinos. Constrains from free-streaming length, CMB, BBN and neutrino experiments are considered., 27 pages, 14 figures

In this paper, we propose a scotogenic model of neutrino masses with flavor-dependent $U(1)_{B-3L_��}(��=e, ��, ��)$ gauge symmetry, in which neutrinos are generated at one-loop level and a fermion dark matter is naturally accommodated. In this model, three one-zero-texture structures of neutrino mass matrix, denoted as patterns A, B and C, are successfully realized by appropriate charge assignment for inert fermions and scalar fields. For each predicted textures, a detailed numerical analysis is carried out to find the allowed regions of neutrino mixing and masses. We find three scenarios (A for normal mass hierarchy, and B and C for inverted mass hierarchy) favored by the latest data of neutrino oscillation experiments and Planck 2018 limit on the sum of neutrino masses. Other phenomenologies such as lepton flavor violation, dark matter and collider signatures are also discussed.

We study the gauged $U(1)_{L_��-L_��}$ scotogenic model with emphasis on latest measurement of LHCb $R_{K^{(*)}}$ anomaly and AMS-02 positron excess. In this model, neutrino masses are induced at one-loop level with $Z_2$-odd particles, i.e., right-handed neutrinos $N_\ell(\ell=e,��,��)$ and inert scalar doublet $��$ inside the loop. Meanwhile, the gauged $U(1)_{L_��-L_��}$ symmetry is broken spontaneously by the scalar singlet $S$, resulting to the massive gauge boson $Z'$. Provided certain couplings to quarks induced by heavy vector-like quarks, the gauge boson $Z'$ would contribute to the transition $b\to s ��^+��^-$, hence explain the $R_{K^{(*)}}$ anomaly. As for the Majorana fermion DM $N$, the gauge boson $Z'$ and the singlet Higgs $H_0$ will generate various annihilation channels, among which the $NN\to Z'Z'$ and $NN\to Z'H_0(\to Z'Z')$ channel could be used to interpret the AMS-02 positron excess. We give a comprehensive analysis on model parameter space with consider various current constraints. The combined analysis shows that the $R_{K^{(*)}}$ anomaly and AMS-02 positron excess can be explained simultaneously.

In this paper, we perform a detail analysis on the phenomenology of $Z'$ portal scalar and Dirac fermion dark matter in $B-L$ scotogenic Dirac model. Unconventional $B-L$ charge $Q$ is assigned to the right-handed neutrino $\nu_R$ in order to realise scotogenic Dirac neutrino mass at one-loop level, where three typical value $Q=-\frac{1}{4},-4,\frac{3}{2}$ are chosen to illustrate. Observational properties involving dilepton signature at LHC, relativistic degrees of freedom $N_\text{eff}$, dark matter relic density, direct and indirect detections are comprehensively studied. Combined results of these observables for the benchmark scenarios imply that the resonance region $M_\text{DM}\sim M_{Z'}/2$ is the viable parameter space. Focusing on the resonance region, a scanning for TeV-scale dark matter is also performed to obtain current allowed and future prospective parameter space., Comment: 28 pages, 15 figures

We consider the feasibility of interpreting the $R_{K^{(*)}}$ anomaly in the colored Zee-Babu model. The model generates neutrino masses at two loops with the help of a scalar leptoquark $S\sim(3,3,-\frac{1}{3})$ and a scalar diquark $\omega\sim(6,1,-\frac{2}{3})$, and contributes to the transition $b\to s\ell\ell$ via the exchange of a leptoquark $S$ at tree level. Under constraints from lepton flavor violating (LFV) and flavor changing neutral current (FCNC) processes, and direct collider searches for heavy particles, we acquire certain parameter space that can accommodate the $R_{K^{(*)}}$ anomaly for both normal (NH) and inverted (IH) hierarchies of neutrino masses. We further examine the LFV decays of the $B$ meson, and find its strong correlation with the neutrino mass hierarchy, i.e., $\text{Br}(B^+ \to K^+ \mu^\pm\tau^\mp)\gtrsim\text{Br}(B^+ \to K^+ \mu^\pm e^\mp)\approx\text{Br}(B^+ \to K^+ \tau^\pm e^\mp)$ for NH, while $\text{Br}(B^+ \to K^+ \mu^\pm \tau^\mp)\ll\text{Br}(B^+ \to K^+ \mu^\pm e^\mp)\approx\text{Br}(B^+ \to K^+ \tau^\pm e^\mp)$ for IH. Among these decays, only $B^+ \to K^+ \mu^\pm e^\mp$ in the case of NH is promising at the LHCb RUN II, while for IH all LFV decays are hard to detect in the near future., Comment: 16 pages, 6 figures, accepted by NPB

We construct the one-loop and two-loop scotogenic models for Dirac neutrino mass generation in the context of $U(1)_{B-L}$ extensions of standard model. It is indicated that the total number of intermediate fermion singlets is uniquely fixed by anomaly free condition and the new particles may have exotic $B-L$ charges so that the direct SM Yukawa mass term $\bar{\nu}_L\nu_R\overline{\phi^0}$ and the Majorana mass term $(m_N/2)\overline{\nu_R^C}\nu_R$ are naturally forbidden. After the spontaneous breaking of $U(1)_{B-L}$ symmetry, the discrete $Z_{2}$ or $Z_{3}$ symmetry appears as the residual symmetry and give rise to the stability of intermediated fields as DM candidate. Phenomenological aspects of lepton flavor violation, DM, leptogenesis and LHC signatures are discussed., Comment: 18 pages, 16 figures

Lepton number violation plays an essential role in many scenarios of neutrino mass generation and also provides new clues to search new physics beyond the standard model. We consider the neutrinophilic two-Higgs-doublet model ($\nu$-2HDM) where additional right-handed neutral fermions $N_{Ri}$ and a complex singlet scalar $\sigma$ are also involved. In scalar sector, the global $U(1)_{L}$ symmetry is spontaneous broken, leading to Nambu-Goldstone boson, the Majoron $J$, accompanied by the Majorana neutrino mass generation. We find that the massless Majoron will induce large invisible Higgs decay, and current experiments have already set constraints on relevant parameters. For the first time, we point out that the $\nu$-2HDM with $N_{Ri}$ can be distinguished from other seesaw by the same sign tri-lepton signature $3\ell^\pm4j+\cancel{E}_T$. More interesting, for $\mathcal{O}(\keV)$ scale Majoron, it is a good candidate of decaying dark matter to interpret the $3.5\keV$ and $511\keV$ line excesses., Comment: 27 pages, 12 figures, two figures corrected, references added

In this paper, we thoroughly investigate the LHC phenomenology of the type II seesaw mechanism for neutrino masses in the nondegenerate case where the triplet scalars of various charge ($H^{\pm\pm}, H^\pm, H^0, A^0$) have different masses. Compared with the degenerate case, the cascade decays of scalars lead to many new, interesting signal channels. In the positive scenario where $M_{H^{\pm\pm}}M_{H^\pm}>M_{H^0/A^0}$, the detection of $H^{\pm\pm}$ is more challenging, when the cascade decay $H^{\pm\pm}\to H^{\pm}W^{\pm*}$ is dominant. The most important channel is the associated $H^{\pm}H^0/A^0$ production in the final state $\ell^\pm\cancel{E}_Tb\bar{b}b\bar{b}$, which requires a luminosity of 109/fb for a $5\sigma$ discovery, while the final state $\ell^\pm\cancel{E}_Tb\bar{b}\tau^+\tau^-$ is less promising. Moreover, the associated $H^0A^0$ production can give same signals as the standard model Higgs pair production. With a much larger cross section, the $H^0A^0$ production in the final state $b\bar{b}\tau^+\tau^-$ could reach $3\sigma$ significance at 14 TeV LHC with a luminosity of 300/fb. In summary, with an integrated luminosity of order 500/fb, the triplet scalars can be fully reconstructed at 14 TeV LHC in the negative scenario., Comment: 41 pages, 20 figures, 7 tables. Version 2 accepted by PRD. 41 pages, 18 figures. Main changes are, (1) rewording in secs III and IV, removing 2 figs and quoting ref [34]; (2) a paragraph added before eq (10) to clarify constraints from electroweak precision data; (3) a paper added to ref [11]. No changes in results

We make a comprehensive analysis on the phenomenology in the minimal version of cascade seesaw for tiny neutrino mass. The seesaw induces at tree level a neutrino mass operator at dimension nine, by introducing a quadruple scalar $\Phi$ of hypercharge unity and a quintuple fermion $\Sigma$ of hypercharge zero. We work in a framework that handles the complicated Yukawa couplings in a nice way without losing generality. All mixing matrices are essentially expressed in terms of the vacuum expectation value of the quadruple scalar v_\Phi, a free complex parameter, and known neutrino parameters. We show that the low-energy lepton flavor violating transitions of the charged leptons set strong constraints on the free parameters. The constraints have a significant impact on collider physics, and are incorporated in our signal analysis at the LHC. We investigate the signatures of new particles by surveying all potentially important channels. We find that the 4j2\ell^\pm signal is most important for the detection of the scalars and the 2\ell^{\pm}2\ell^{\mp}2j, 3\ell^{\pm}\ell^{\mp}2j and 3\ell^{\pm}2\ell^{\mp}+\cancel{E_T} signals are quite promising for the fermions., Comment: v1: 48 pages, including 18 figures and 10 tables; v2: version to appear in PRD, 50 pages, including 19 figures and 10 tables, changes are: (1) detailed discussion of LFV constraints on parameters together with a new figure (Fig. 3); (2) more refs; (3) typos and grammatical issues fixed