The impact of heavy-quark loops on LHC dark-matter searches

Abstract

If only tree-level processes are included in the analysis, LHC monojet searches give weak constraints on the dark matter-proton scattering cross section arising from the exchange of a new heavy scalar or pseudoscalar mediator with Yukawa-like couplings to quarks. In this letter we calculate the constraints on these interactions from the CMS 5.0 fb −1 and ATLAS 4.7 fb −1 searches for jets with missing energy including the effects of heavy-quark loops. We find that the inclusion of such contributions leads to a dramatic increase in the predicted cross section and therefore a significant improvement of the bounds from LHC searches.

Next-to-leading order predictions for dark matter production at hadron colliders

“…Secondly we note that the limits on Λ from the top-scalar operator are of the order Λ ∼ 150 GeV [33]. This is exactly in the region of M φ , g , Λ phase space in which the EFT begins to breakdown, however, if the FT was used with slightly softer / E T cuts one obtains cross sections in which the EFT and FT are similar.…”

“…Finally, we consider the production of a monojet signature using the O (t) S operator. The enhancement which comes from including the loop induced processes in which the DM couples directly to the top quarks, is very large [33]. We show the LO cross sections obtained using MCFM where for this operator we have set Λ = 150.…”

Scalar simplified models for dark matter

“…As previous works [28,[38][39][40][41][42] have pointed out, scalar and pseudoscalar mediator models and EFTs face unique simulation issues at colliders. Making the well-motivated assumption that the mediator couplings to Standard Model fermions proportional to the Higgs Yukawas, the mediator is primarily produced at the LHC through a loop-induced interaction with gluons.…”

New Constraints on Dark Matter Effective Theories from Standard Model Loops

“…However, different search strategies probe different energy scales, and such a separation of scales may have striking consequences when a connection between different experiments or ultraviolet (UV) complete models with experiments is attempted. Indeed, in some cases loop corrections are known to dramatically alter direct detection (DD) rates [21][22][23][24][25][26][27][28][29].In this Letter we consider the case of a SM gauge singlet Dirac DM (χ), with m χ < Λ, and we calculate the complete set of one-loop effects induced by SM fields for operators up to dimension 6 that contribute to spin-independent (SI) DM-nucleon scattering. The separation between Λ and the DD scale is systematically taken into account via a proper renormalization group (RG) analysis.…”