Abstract
We study a class of simplified dark matter models in which dark matter couples directly with a mediator and a charged lepton. This class of Lepton Portal dark matter models has very rich phenomenology: it has loop generated dark matter electromagnetic moments that generate a direct detection signal; it contributes to indirect detection in the cosmic positron flux via dark matter annihilation; it provides a signature of the same-flavor, opposite-sign dilepton plus missing transverse energy at colliders. We determine the current experimental constraints on the model parameter space for Dirac fermion, Majorana fermion and complex scalar dark matter cases of the Lepton Portal framework. We also perform a collider study for the 14 TeV LHC reach with 100 inverse femtobarns for dark matter parameter space. For the complex scalar dark matter case, the LHC provides a very stringent constraint and its reach can be interpreted as corresponding to a limit as strong as two tenths of a zeptobarn on the dark matter-nucleon scattering cross section for dark matter masses up to 500 GeV. We also demonstrate that one can improve the current collider searches by using a Breit-Wigner like formula to fit the dilepton MT2 tail of the dominant diboson background.
Highlights
Of Quark Portal dark matter models, which is a class of simplified models in which dark matter particles and mediators interact with a single quark
We study a class of simplified dark matter models in which dark matter couples directly with a mediator and a charged lepton. This class of Lepton Portal dark matter models has very rich phenomenology: it has loop generated dark matter electromagnetic moments that generate a direct detection signal; it contributes to indirect detection in the cosmic positron flux via dark matter annihilation; it provides a signature of the sameflavor, opposite-sign dilepton plus missing transverse energy at colliders
For the three categories of dark matter particles: Majorana fermion, Dirac fermion and complex scalar, we have found that the 14 TeV LHC has a much better reach than the direct detection experiments for the Majorana fermion and complex scalar cases
Summary
In order for SM leptons to be a portal to the dark sector, there must be at least two particles, one fermion and one boson, in the dark sector. The left-handed lepton case requires the dark matter partner to be a weak doublet for renormalizable couplings and more degrees of freedom. For a complex scalar dark matter particle, X, the partner is a Dirac fermion, ψ, with electric charge −1 and the interactions. To be in the charged-lepton mass eigenstates, so there are no new contributions to the flavor violating processes from the dark matter sector. This assumption can be arranged by implementing Minimal Flavor Violation (MFV) in the lepton sector [21]. We will consider one flavor at one time This assumption can be arranged for electron and tau coupling. We will work out the standard dark matter phenomenology including thermal relic abundance, direct detection, indirect detection and collider searches, in sequence
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