Towards the next generation of simplified Dark Matter models

Abstract

Abstract:This White Paper is an input to the ongoing discussion about the extension and refinement of simplified Dark Matter (DM) models. Based on two concrete examples, we show how existing simplified DM models (SDMM) can be extended to provide a more accurate and comprehensive framework to interpret and characterise collider searches. In the first example we extend the canonical SDMM with a scalar mediator to include mixing with the Higgs boson. We show that this approach not only provides a better description of the underlying kinematic properties that a complete model would possess, but also offers the option of using this more realistic class of scalar mixing models to compare and combine consistently searches based on different experimental signatures. The second example outlines how a new physics signal observed in a visible channel can be connected to DM by extending a simplified model including effective couplings. This discovery scenario uses the recently observed excess in the high-mass diphoton searches of ATLAS and CMS for a case study to show that such a pragmatic approach can aid the experimental search programme to verify/falsify a potential signal and to study its underlying nature. In the next part of the White Paper we outline other interesting options for SDMM that could be studied in more detail in the future. Finally, we discuss important aspects of supersymmetric models for DM and how these could help to develop of more complete SDMM.This White Paper is a summary of the brainstorming meeting "Next generation of simplified Dark Matter models" that took place at Imperial College, London on May 6, 2016, and corresponding follow-up studies on selected subjects.

Dark Matter Searches at Colliders

“…Mixing with the Higgs sector is an example of how gauge invariance can be restored for these models. Couplings to the electroweak gauge bosons can also be added as a consequence of electroweak symmetry breaking (45,46). The tree-level signatures in this case include Higgs or vector bosons plus missing transverse momentum and, if the invisible particles are sufficiently light, invisible decays of the Higgs boson.…”

“…Ultimately, we do not yet know whether the Standard Model Higgs boson is alone in the scalar sector, nor whether a single scalar mediator encodes all of the important features of the complicated phenomenology of more complex scalar sectors. A step beyond the simple scalar mediator model, dictated by gauge invariance, is to take mixing between this mediator and the Standard Model Higgs boson into account (38,45). A much larger step beyond that is to consider an extended Higgs sector such as a 2HDM, in which one or more of the scalars acts as the mediator between DM and ordinary matter (44,53,54).…”

GeV-scale thermal WIMPs: Not even slightly ruled out

“…Important examples include scattering rates which are suppressed by powers of velocity or momentum, or cancellation between scattering diagrams [108][109][110][111]. For Wino or Higgsino DM candidates, scattering occurs through suppressed loops [112], but its annihilation is not suppressed.…”

The waning of the WIMP? A review of models, searches, and constraints

“…The processes responsible for the DM relic density and its eventual detection can be described by simple extensions of the SM in which a DM candidate interacts with the SM states (typically the interactions are limited to the SM fermions) through a mediator state (dubbed portal). This idea is at the base of the so-called "Simplified Models" [140][141][142][143][144][145][146][147][148][149][150][151][152][153][154] which are customarily adopted especially in the context of collider studies, see e.g., Refs. [130,[155][156][157][158][159][160][161][162][163][164][165][166].…”