Leptophilic effective WIMPs

Effective weakly interacting massive particle (WIMP) models are minimal extensions of the standard model that explain the relic density of dark matter by the “WIMP miracle.” In this paper we consider the phenomenology of effective WIMPs with trilinear couplings to leptons and a new “lepton partner” particle. The observed relic abundance fixes the strength of the cubic coupling, so the parameters of the models are defined by the masses of the WIMP and lepton partner particles. This gives a simple parameter space where collider and direct detection experiments can be compared under well-defined physical minimality assumptions. The most sensitive collider probe is the search for $\text{leptons}+\mathrm{MET}$, while the most sensitive direct detection channel is scattering from nuclei arising from loop diagrams. Collider and direct detection searches are highly complementary: colliders give the only meaningful constraint when dark matter is its own antiparticle, while direct detection is generally more sensitive if the dark matter is not its own antiparticle.

Figure 1

Feynman diagram contributing to dark matter freeze-out

Figure 2

Feynman diagram contributing to $\text{leptons}+\mathrm{MET}$ signal at colliders.

Figure 3

Extrapolation of limits for the 2 $\text{lepton}+\mathrm{MET}$ search as a function of $m_L$ for fixed $m_{\chi }$, compared with ATLAS reported limits.

Figure 4

Extrapolation of limits for the 2 $\text{lepton}+\mathrm{MET}$ search as a function of $m_{\chi }$ for fixed $m_L$, compared with ATLAS reported limits.

Figure 5

Schematic one-loop contributions for direct detection. There are also diagrams where the lepton partner (L) and lepton ($\ell$) are interchanged.

Figure 6

Schematic two-loop contributions to direct detection scattering. There are also diagrams where the lepton-partner (L) and lepton ($\ell$) are interchanged and where the photons are crossed.

Figure 7

Limits on Dirac dark matter coupling to the first two generations of leptons only.

Figure 8

Limits on Dirac dark matter coupling to all three generations of leptons.

Figure 9

Limits on complex scalar dark matter coupling to the first two generations of leptons.

Figure 10

Limits on complex scalar dark matter coupling to all three generations of leptons.