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Register a new userGauged $U(1)_{L_mu-L_tau}$ Scotogenic Model in light of $R_{K^{(*)}}$ Anomaly and AMS-02 Positron Excess
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We study the gauged $U(1)_{L_mu-L_tau}$ 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 $N_ell(ell=e,mu,tau)$ and inert scalar doublet $eta$ inside the loop. Meanwhile, the gauged $U(1)_{L_mu-L_tau}$ 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 $bto s mu^+mu^-$, 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 $NNto ZZ$ and $NNto ZH_0(to ZZ)$ 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.
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Gauged $U(1)_{L_mu - L_tau}$ model has been advocated for a long time in light of muon $g-2$ anomaly, which is a more than $3sigma$ discrepancy between the experimental measurement and the standard model prediction. We augment this model with three right-handed neutrinos $(N_e, N_mu, N_tau)$ and a vector-like singlet fermion $(chi)$ to explain simultaneously the non-zero neutrino mass and dark matter content of the Universe, while satisfying anomalous muon $g-2$ constraints. It is shown that in a large parameter space of this model we can explain positron excess, observed at PAMELA, Fermi-LAT and AMS-02, through dark matter annihilation, while satisfying the relic density and direct detection constraints.
As experimental null results increase the pressure on heavy weakly interacting massive particles (WIMPs) as an explanation of thermal dark matter (DM), it seems timely to explore previously overlooked regions of the WIMP parameter space. In this work we extend the minimal gauged $U(1)_{L_mu-L_tau}$ model studied in cite{Bauer:2018onh} by a light (MeV-scale) vector-like fermion $chi$. Taking into account constraints from cosmology, direct and indirect detection we find that the standard benchmark of $M_V=3 m_chi$ for DM coupled to a vector mediator is firmly ruled out for unit DM charges. However, exploring the near-resonance region $M_Vgtrsim 2 m_chi$ we find that this model can simultaneously explain the DM relic abundance $Omega h^2 =0.12$ and the $(g-2)_mu$ anomaly. Allowing for small charge hierarchies of $lesssimmathcal{O}(10)$, we identify a second window of parameter space in the few-GeV region, where $chi$ can account for the full DM relic density.
We propose a local $U(1)_{L_mu-L_tau}$ model to explain $b to s mu^+ mu^-$ anomaly observed at the LHCb and Belle experiments. The model also has a natural dark matter candidate $N$. We introduce $SU(2)_L$-doublet colored scalar $widetilde{q}$ to mediate $b to s$ transition at one-loop level. The $U(1)_{L_mu-L_tau}$ gauge symmetry is broken spontaneously by the scalar $S$. All the new particles are charged under $U(1)_{L_mu-L_tau}$. We can obtain $C_9^{mu,{rm NP}} sim -1$ to solve the $b to smu^+mu^-$ anomaly and can explain the correct dark matter relic density of the universe, $Omega_{rm DM} h^2 approx 0.12$, simultaneously, while evading constraints from electroweak precision tests, neutrino trident experiments and other quark flavor-changing loop processes such as $b to s gamma$ and $B_s-overline{B}_s$ mixing. Our model can be tested by searching for $Z$ and new colored scalar at the LHC and $B to K^* u overline{ u}$ process at Belle-II.
Models of gauged $U(1)_{L_mu-L_tau}$ can provide a solution to the long-standing discrepancy between the theoretical prediction for the muon anomalous magnetic moment and its measured value. The extra contribution is due to a new light vector mediator, which also helps to alleviate an existing tension in the determination of the Hubble parameter. In this article, we explore ways to probe this solution via the scattering of solar neutrinos with electrons and nuclei in a range of experiments and considering high and low solar metallicity scenarios. In particular, we reevaluate Borexino constraints on neutrino-electron scattering, finding them to be more stringent than previously reported, and already excluding a part of the $(g-2)_mu$ explanation with mediator masses smaller than $2times10^{-2}$ GeV. We then show that future direct dark matter detectors will be able to probe most of the remaining solution. Due to its large exposure, LUX-ZEPLIN will explore regions with mediator masses up to $5times10^{-2}$ GeV and DARWIN will be able to extend the search beyond $10^{-1}$ GeV, thereby covering most of the area compatible with $(g-2)_mu$. For completeness, we have also computed the constraints derived from the recent XENON1T electron recoil search and from the CENNS-10 LAr detector, showing that none of them excludes new areas of the parameter space. Should the excess in the muon anomalous magnetic moment be confirmed, our work suggests that direct detection experiments could provide crucial information with which to test the $U(1)_{L_mu-L_tau}$ solution, complementary to efforts in neutrino experiments and accelerators.
In this paper we introduce a light Dirac particle $psi$ as thermal dark matter candidate in a $U(1)_{L_{mu}-L_{tau}}$ model. Together with the new gauge boson $X$, we find a possible parameter space with $m_X simeq 20$ MeV, $U(1)_{L_{mu}-L_{tau}}$ coupling $g_X simeq 5 cdot 10^{-4}$ and $m_psi gtrsim m_X/2$ where the $(g-2)_mu$ anomaly, dark matter, the Hubble tension, and (part of) the excess of $511$ keV photons from the region near the galactic center can be explained simultaneously. This model is safe from current experimental and astrophysical constraints, but can be probed by the next generation of neutrino experiments as well as low-energy $e^+e^-$ colliders.
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