Abstract

The strong direct detection limits could be pointing to dark matter – nucleus scattering at loop level. We study in detail the prototype example of an electroweak singlet (Dirac or Majorana) dark matter fermion coupled to an extended dark sector, which is composed of a new fermion and a new scalar. Given the strong limits on colored particles from direct and indirect searches we assume that the fields of the new dark sector are color singlets. We outline the possible simplified models, including the well-motivated cases in which the extra scalar or fermion is a Standard Model particle, as well as the possible connection to neutrino masses. We compute the contributions to direct detection from the photon, the Z and the Higgs penguins for arbitrary quantum numbers of the dark sector. Furthermore, we derive compact expressions in certain limits, i.e., when all new particles are heavier than the dark matter mass and when the fermion running in the loop is light, like a Standard Model lepton. We study in detail the predicted direct detection rate and how current and future direct detection limits constrain the model parameters. In case dark matter couples directly to Standard Model leptons we find an interesting interplay between lepton flavor violation, direct detection and the observed relic abundance.

Highlights

  • Direct detection (DD) experiments search for dark matter (DM) scatterings off nuclei in underground detectors

  • We study in detail the prototype example of an electroweak singlet (Dirac or Majorana) dark matter fermion coupled to an extended dark sector, which is composed of a new fermion and a new scalar

  • In case dark matter couples directly to Standard Model leptons we find an interesting interplay between lepton flavor violation, direct detection and the observed relic abundance

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Summary

Introduction

Direct detection (DD) experiments search for dark matter (DM) scatterings off nuclei in underground detectors. [10] the authors performed a detailed study of one-loop scenarios with a charged mediator directly coupled to Standard Model (SM) fields, including the Z and Higgs boson contributions. [14] the authors studied the one-loop contributions to DD in models with pseudo-scalar mediators or inelastic scattering. In the context of supersymmetry detailed computations have been performed for the bino [15] and wino [16,17,18] DM cases In the latter scenario loop contributions to DM-nucleus scattering due to gauge bosons may give significant corrections. In this work we study the DD scattering rate for the case of DM being a SM singlet Dirac or Majorana fermion ψ, which is coupled to a more complex dark sector. Details about the calculation of the relic abundance are collected in Appendix E and the numerical expressions for the matching to NR operators are given in Appendix F

Dirac dark matter
Majorana dark matter
Standard Model particles in the loop
Left-handed lepton doublet
Right-handed charged lepton
Right-handed neutrino
Higgs doublet
Wilson coefficients at the quark level
Non-relativistic Wilson coefficients at the nucleon level
Analytical results
Photon penguin
Z penguin
Higgs penguin
Z and Higgs penguin
Numerical analysis
Wilson coefficients at the nucleon level
Direct detection event rates
Direct detection limits
Interplay with lepton flavor violation and relic abundance
LHC searches
Z and Higgs boson invisible decays
Relic abundance
Thermal freeze-out
Non-thermal production
Conclusions

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