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Register a new userNeutrino Mass, Dark Matter and Anomalous Magnetic Moment of Muon in a $U(1)_{L_{mu}-L_{tau}}$ Model
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The observation of neutrino masses, mixing and the existence of dark matter are amongst the most important signatures of physics beyond the Standard Model (SM). In this paper, we propose to extend the SM by a local $L_mu - L_tau$ gauge symmetry, two additional complex scalars and three right-handed neutrinos. The $L_mu - L_tau$ gauge symmetry is broken spontaneously when one of the scalars acquires a vacuum expectation value. The $L_mu - L_tau$ gauge symmetry is known to be anomaly free and can explain the beyond SM measurement of the anomalous muon $({rm g-2})$ through additional contribution arising from the extra $Z_{mutau}$ mediated diagram. Small neutrino masses are explained naturally through the Type-I seesaw mechanism, while the mixing angles are predicted to be in their observed ranges due to the broken $L_mu-L_tau$ symmetry. The second complex scalar is shown to be stable and becomes the dark matter candidate in our model. We show that while the $Z_{mutau}$ portal is ineffective for the parameters needed to explain the anomalous muon $({rm g-2})$ data, the correct dark matter relic abundance can easily be obtained from annihilation through the Higgs portal. Annihilation of the scalar dark matter in our model can also explain the Galactic Centre gamma ray excess observed by Fermi-LAT. We show the predictions of our model for future direct detection experiments and neutrino oscillation experiments.
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We study an extension of the minimal gauged $L_{mu}-L_{tau}$ model in order to explain the anomalous magnetic moments of muon and electron simultaneously. Presence of an additional scalar doublet $eta$ and an in-built $Z_2$ symmetry under which the right handed singlet fermions and $eta$ are odd, leads to light neutrino mass in scotogenic fashion along with a stable dark matter candidate. In spite of the possibility of having positive and negative contributions to $(g-2)$ from vector boson and charged scalar loops respectively, the minimal scotogenic $L_{mu}-L_{tau}$ model can not explain muon and electron $(g-2)$ simultaneously while being consistent with other experimental bounds. We then extend the model with a vector like lepton doublet which not only leads to a chirally enhanced negative contribution to electron $(g-2)$ but also leads to the popular singlet-doublet fermion dark matter scenario. With this extension, the model can explain both electron and muon $(g-2)$ while being consistent with neutrino mass, dark matter and other direct search bounds. The model remains predictive at high energy experiments like collider as well as low energy experiments looking for charged lepton flavour violation, dark photon searches, in addition to future $(g-2)$ measurements.
The tightening of the constraints on the standard thermal WIMP scenario has forced physicists to propose alternative dark matter (DM) models. One of the most popular alternate explanations of the origin of DM is the non-thermal production of DM via freeze-in. In this scenario the DM never attains thermal equilibrium with the thermal soup because of its feeble coupling strength ($sim 10^{-12}$) with the other particles in the thermal bath and is generally called the Feebly Interacting Massive Particle (FIMP). In this work, we present a gauged U(1)$_{L_{mu}-L_{tau}}$ extension of the Standard Model (SM) which has a scalar FIMP DM candidate and can consistently explain the DM relic density bound. In addition, the spontaneous breaking of the U(1)$_{L_{mu}-L_{tau}}$ gauge symmetry gives an extra massive neutral gauge boson $Z_{mutau}$ which can explain the muon ($g-2$) data through its additional one-loop contribution to the process. Lastly, presence of three right-handed neutrinos enable the model to successfully explain the small neutrino masses via the Type-I seesaw mechanism. The presence of the spontaneously broken U(1)$_{L_{mu}-L_{tau}}$ gives a particular structure to the light neutrino mass matrix which can explain the peculiar mixing pattern of the light neutrinos.
We investigate Majorana dark matter in a new variant of $U(1)_{L_{mu}-L_{tau}}$ gauge extension of Standard Model, containing three additional neutral fermions $N_{e}, N_{mu}, N_{tau}$, along with a $(bar{3},1,1/3)$ scalar Leptoquark (SLQ) and an inert doublet, to study the phenomenology of dark matter, neutrino mass generation and flavour anomalies on a single platform. The lightest mass eigenstate of the $N_{mu}, N_{tau}$ neutral fermions plays the role of dark matter. We compute the WIMP-nucleon cross section in leptoquark portal and the relic density mediated by inert doublet components, leptoquark and the new $Z^{prime}$ boson. We constrain the parameter space consistent with Planck limit on relic density, PICO-60 and LUX bounds on spin-dependent direct detection cross section. We also discuss about the neutrino mass generation at one-loop level and the viable parameter region to explain current neutrino oscillation data. The $Z^prime$ gauge boson of extended $U(1)$ symmetry and the SLQ play an important role in settling the known issues of flavor sector.
The energy spectrum of cosmic neutrinos, which was recently reported by the IceCube collaboration, shows a gap between 400 TeV and 1 PeV. An unknown neutrino interaction mediated by a field with a mass of the MeV scale is one of the possible solutions to this gap. We examine if the leptonic gauge interaction L_{mu} - L_{tau} can simultaneously explain the two phenomena in the lepton sector: the gap in the cosmic neutrino spectrum and the unsettled disagreement in muon anomalous magnetic moment. We illustrate that there remains the regions in the model parameter space, which account for both the problems. Our results also provide a hint for the distance to the source of the high-energy cosmic neutrinos.
Motivated by the growing evidence for lepton flavour universality violation after the first results from Fermilabs muon $(g-2)$ measurement, we revisit one of the most widely studied anomaly free extensions of the standard model namely, gauged $L_{mu}-L_{tau}$ model, known to be providing a natural explanation for muon $(g-2)$. We also incorporate the presence of dark matter (DM) in this model in order to explain the recently reported electron recoil excess by the XENON1T collaboration. We show that the same neutral gauge boson responsible for generating the required muon $(g-2)$ can also mediate interactions between electron and dark fermions boosted by dark matter annihilation. The required DM annihilation rate into dark fermion require a hybrid setup of thermal and non-thermal mechanisms to generate DM relic density. The tightly constrained parameter space from all requirements remain sensitive to ongoing and near future experiments, keeping the scenario very predictive.
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