The Large Hadron electron Collider (LHeC) has been designed to push the field of deep inelastic scattering to the high energy and intensity frontier using an intense electron beam with a proton beam from the High Luminosity-Large Hadron Collider. However, LHeC is also a great laboratory for new physics. In this work, we propose a search for dark matter that couples with leptons. This may yield $ej$+ missing energy and $μj$ + missing energy signals that can be potentially observed through simple missing-energy cuts that suppress the Standard Model background. Considering direct dark matter detection and LHC constraints, we show that LHeC can indeed discover a weak scale dark matter fermion for masses up to 350 GeV, which reproduces the correct relic density, and has interesting implications for lepton flavor violation.
We investigate the prospects for detecting light leptophilic dark sectors with a missing-momentum experiment at NA64 running in muon mode. In particular, we consider models in which dark matter connects to the visible sector through a lepton- or muon-specific scalar mediator. These scalars can also account for the $\sim 3.5σ$ discrepancy between the measured and predicted values of $(g-2)_μ$ . We emphasize the complementarity between NA64-$μ$ and other terrestrial and astrophysical probes.
Two-Higgs-Doublet Model of Type-X in the large $\tanβ$ limit becomes leptophilic to allow a light pseudo-scalar $A$ and thus provides an explanation of the muon $g-2$ anomaly. Introducing a singlet scalar dark matter $S$ in this context, one finds that two important dark matter properties, nucleonic scattering and self-annihilation, are featured separately by individual couplings of dark matter to the two Higgs doublets. While one of the two couplings is strongly constrained by direct detection experiments, the other remains free to be adjusted for the relic density mainly through the process …
We propose a new class of $U(1)_{μ-τ}$ gauged model that can explain recent flavor anomalies such as muon $g-2$, $b\to sμ^+ μ^-$, as well as include a scalar dark matter candidate while satisfying all the phenomenological constraints. For this purpose, we add new vectorlike quarks and leptons as well as two inert singlet scalars, one leptophilic and the other leptophobic. In our model $b\to sμ^+ μ^-$ anomalies can be explained by loop induced interactions among the SM and exotic quarks and $Z'$ gauge boson. In our numerical analysis, we show allowed region of our model to be narrow, and it wou…
We discuss the phenomenology of a minimal model for GeV-scale Majorana dark matter (DM) coupled to the standard model lepton sector via a charged scalar singlet. The theoretical framework extends the Standard Model by two $SU(2)_L$ singlets: one charged Higgs boson and a singlet right-handed fermion. The latter plays the role of the DM candidate. We show that there is an anti-correlation between the spin-independent DM-Nucleus scattering cross-section ($σ_{\rm SI}$) and the DM relic density. We suggest a scenario that can be tested in both electron-electron and electron-positron collisions usi…
New gauge symmetries often appear in theories beyond the Standard Model. Here we study a model where lepton number is promoted to a gauge symmetry. Anomaly cancellation requires the introduction of additional leptons, the lightest of which is a natural leptophilic dark matter candidate. We perform a comprehensive study of both collider and dark matter phenomenology. Furthermore we find that the model exhibits a first order lepton number breaking phase transition in large regions of parameter space. The corresponding gravitational wave signal is computed, and its detectability at LISA and other…
Many scenarios of physics beyond the Standard Model predict the existence of new gauge singlets, which might be substantially lighter than the weak scale. The experimental constraints on additional scalars with masses in the MeV to GeV range could be significantly weakened if they interact predominantly with leptons rather than quarks. At an $e^+e^-$ collider, such a leptophilic scalar ($ϕ_L$) would be produced predominantly through radiation from a $τ$ lepton. We report herein a search for $e^+e^- \to τ^+τ^- ϕ_L$, $ϕ_L \to \ell^+\ell^-$ ($\ell=e,μ$) using data collected by the BABAR experimen…
Medium-energy electron beam-dump experiments provide an intense sources of secondary muons. These particles can be used to search for muon-coupling light dark scalars that may explain the $(g-2)_μ$ anomaly. We applied this idea to SLAC E137 experiment deriving new exclusion limits and evaluated the expected sensitivity for the planned Jefferson Lab BDX experiment (in case of null result report). The calculation is based on numerical simulations that include a realistic description of secondary muons generation in the dump, dark scalar production, propagation, and decay, and, finally, the decay…
In this paper we study a leptophilic dark matter scenario involving feeble dark matter coupling to the Standard Model (SM) and compressed dark matter-mediator mass spectrum. We consider a simplified model where the SM is extended with one Majorana fermion, the dark matter, and one charged scalar, the mediator, coupling to the SM leptons through a Yukawa interaction. We first discuss the dependence of the dark matter relic abundance on the Yukawa coupling going continuously from freeze-in to freeze-out with an intermediate stage of conversion driven freeze-out. Focusing on the latter, we then e…
We discuss model-independent collider constraints on the effective couplings of leptophilic dark matter (LDM), considering its production at a future electron-positron linear collider, with both polarized and unpolarized beam options, in the mono-photon and mono-$Z$ channels. We show that the future collider constraints are largely complementary to the direct and indirect detection limits on LDM, and can potentially provide the best-ever LDM sensitivity in the low-mass regime (below $\sim$ 10 GeV).
In this paper we revisit constraints on the leptophilic dark matter (DM) arising from the DM indirect detection experiments. Interactions between the charged leptons and the scalar-type, Dirac-type or vector-type DM are written in terms of effective operators. After classifying all interactions that may give non-zero signals in indirect detections, we study constraints on the parameter space of these effective interactions from the latest results of AMS-02, Planck, Fermi-LAT and H.E.S.S., as well as the observed relic abundance. Main results are summarized in the Table. I. It shows that the $τ…
A light leptophilic boson (scalar or pseudoscalar) has been postulated to explain the muon g-2 anomaly and could be a portal to dark matter. Realizing the leptophilic nature of a singlet boson in the framework of the two-Higgs-doublet-Model of type-X, we identify the parameter space viable for the explanation of the updated muon g-2 discrepancy. It is then shown that such a hypothetical particle will be unambiguously ruled out or discovered via the Yukawa process at a lepton collider designed as a Higgs factory.
We propose a model which explains the baryon asymmetry of the universe and dark matter relic density at the same time. In this model, dark matter candidate is the dark baryon composed by dark quarks. A scalar mediator, which couples to the standard model leptons and dark quarks, is introduced to generate the asymmetry of baryon and dark baryon simultaneously. Direct detection and collider detection of this model are studied. We find that current underground direct detection experiments and LHC can hardly detect this model. But future lepton colliders, such as CEPC, have great potential to dete…
Inspired by the recently new measurement of $(g-2)_μ$ at FermiLab and reported upper bound for electron-dark matter (DM) recoil by the XENON1T collaboration, we revisited phenomenology of a light MeV scale vector dark matter in a leptophilic extension of standard model while a new spinor field plays the role of mediator. A viable parameter space is considered to discuss the possibility of light dark matter relic density as well as anomalous magnetic moment of the muon. We study DM-electron direct detection and cosmological bounds on the parameters space of the model. It is shown that although …
We consider the possibility that dark matter (DM) only interacts with the Standard Model leptons, but not quarks at tree level, and analyze the future lepton collider prospects of such leptophilic DM in the monophoton and mono-$Z$ (both leptonic and hadronic) channels. Adopting a model-independent effective field theory framework, we consider all possible dimension-six operators of scalar-pseudoscalar (SP), vector-axial vector (VA), and tensor-axial tensor (TAT) types for a fermionic DM and derive the collider sensitivities on the effective cutoff scale $Λ$ as a function of the DM mass. As a c…
We study the influence of leptophilic dark matter interactions on decays of muons and ground state mesons in existing experiments. We consider a secluded dark sector exclusively interacting with leptons via either a (leptophilic) scalar or vector mediator. These interactions will therefore influence leptonic decays and deform the energy spectra. We first study the Michel decay of muons, $μ^+\rightarrow e^+ν_e \barν_μ$, which allow us to constrain the parameter space reasonably well. Secondly, the rare $π^\pm$, $K^\pm$, $D^\pm$ and $D_s^\pm$ decays to $eν$ will be considered. Scalar mediators w…
Extensions of the Standard Model (SM) gauge group with a new $U(1)_X$ predict an additional gauge boson. Through kinetic mixing with the SM photons featured by a coupling $ε$, the ensuing so-called dark photons $γ'$, which acquire mass as a result of the breaking of the gauge group $U(1)_X$, can interact with the SM field content. These massive dark photons can therefore decay to pairs of leptons, hadrons, or quarks, depending on their mass $m_{γ'}$. In this work, we discuss searches for dark photons in the mass range around and below one GeV at the LHeC and FCC-he colliders. The signal is giv…
The muon $g-2$ anomaly was strengthened by recent experimental results at Fermilab, which may be signatures of new physics. A scenario of leptophilic scalar $ϕ_L$ accounting for the muon $g-2$ anomaly is investigated in this paper. Though a light $ϕ_L$ mainly decaying into standard model (SM) particles has been excluded by experiments, a dark leptophilic scalar $ϕ_L$ predominantly decaying into invisible fermionic dark matter (DM) $χ\barχ$ is still allowed. Considering the decay mode $ϕ_L \to χ\barχ$ opened (here $m_{ϕ_L} = 3 m_χ$), the coupling preferred by the muon $g-2$ and the $ϕ_L-χ$ coup…
The physics of the solar dark matter (DM) that are captured and thermalise through the DM-nucleon interaction has been extensively studied. In this work, we consider the leptophilic DM scenario where the DM particles interact exclusively with the electrons through the axial-vector coupling. We investigate relevant phenomenologies in the Sun, including its capture, evaporation and thermalisation, and we calculate the equilibrium distribution using the Monte Carlo methods, rather than adopting a semi-analytic approximation. Based on the analysis, we then determine the minimum testable mass for w…
Cosmic-ray positrons have long been considered a powerful probe of dark matter annihilation. In particular, myriad studies of the unexpected rise in the positron fraction have debated its dark matter or pulsar origins. In this paper, we instead examine the potential for extremely precise positron measurements by AMS-02 to probe hard leptophilic dark matter candidates that do not have spectral features similar to the bulk of the observed positron excess. Utilizing a detailed cosmic-ray propagation model that includes a primary positron flux generated by Galactic pulsars in addition to a seconda…
Recently the DArk Matter Particle Explorer (DAMPE) has reported an excess in the electron-positron flux of the cosmic rays which is interpreted as a dark matter particle with the mass about $1.5$ TeV. We come up with a leptophilic $Z'$ scenario including a Dirac fermion dark matter candidate which beside explaining the observed DAMPE excess, is able to pass various experimental/observational constraints including the relic density value from the WMAP/Planck, the invisible Higgs decay bound at the LHC, the LEP bounds in electron-positron scattering, the muon anomalous magnetic moment constraint…
We revisit dark matter annihilation as an explanation of the positron excess reported recently by the AMS-02 satellite-borne experiment. To this end, we propose a particle dark matter model by considering a Two Higgs Doublet Model (2HDM) extended with an additional singlet boson and a singlet fermion. The additional (light) boson mixes with the pseudoscalar inherent in the 2HDM, and the singlet fermion, which is the dark matter candidate, annihilates via this bosonic portal. The dark matter candidate is made leptophilic by choosing the lepton-specific 2HDM and a suitable high value of $\tanβ$.…
Using a simplified framework, we attempt to explain the recent DAMPE cosmic $e^+ + e^-$ flux excess by leptophilic Dirac fermion dark matter (LDM). The scalar ($Φ_0$) and vector ($Φ_1$) mediator fields connecting LDM and Standard Model particles are discussed. Under constraints of DM relic density, gamma-rays, cosmic-rays and Cosmic Microwave Background (CMB), we find that the couplings $P \otimes S$, $P \otimes P$, $V \otimes A$ and $V \otimes V$ can produce the right bump in $e^+ + e^-$ flux for a DM mass around 1.5 TeV with a natural thermal annihilation cross-section $<σv> \sim 3 \times 10…
Dark matter particles will be captured in neutron stars if they undergo scattering interactions with nucleons or leptons. These collisions transfer the dark matter kinetic energy to the star, resulting in appreciable heating that is potentially observable by forthcoming infrared telescopes. While previous work considered scattering only on nucleons, neutron stars contain small abundances of other particle species, including electrons and muons. We perform a detailed analysis of the neutron star kinetic heating constraints on leptophilic dark matter. We also estimate the size of loop induced co…
Motivated by the very recent cosmic-ray electron+positron excess observed by DAMPE collaboration, we investigate a Dirac fermion dark matter (DM) in the gauged $L_e - L_μ$ model. DM interacts with the electron and muon via the $U(1)_{e-μ}$ gauge boson $Z^{'}$. The model can explain the DAMPE data well. Although a non-zero DM-nucleon cross section is only generated at one loop level and there is a partial cancellation between $Z^{'}ee$ and $Z^{'}μμ$ couplings, we find that a large portion of $Z^{'}$ mass is ruled out from direct DM detection limit leaving the allowed $Z^{'}$ mass to be close to…
In leptophilic scenarios, dark matter interactions with nuclei, relevant for direct detection experiments and for the capture by celestial objects, could only occur via loop-induced processes. If the mediator is a scalar or pseudo-scalar particle, which only couples to leptons, the dominant contribution to dark matter-nucleus scattering would take place via two-photon exchange with a lepton triangle loop. The corresponding diagrams have been estimated in the literature under different approximations. Here, we present new analytical calculations for one-body two-loop and two-body one-loop inter…
Constraints on a Light Leptophilic Scalar from Dark-Sector Couplings
Physics Department and INFN Sezione di Roma, Università di Roma La Sapienza（罗马第一大学物理系及意大利国家核物理研究所罗马分部）；Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati（意大利国家核物理研究所弗拉斯卡蒂国家实验室）；LAPTh, Université Savoie Mont-Blanc et CNRS（萨瓦蒙布朗大学与法国国家科学研究中心拉普特实验室）
