[Paper Review] Thermal WIMPs and the Scale of New Physics: Global Fits of Dirac Dark Matter Effective Field Theories

The GAMBIT Collaboration, Peter Athron+25 more|arXiv (Cornell University)|Jun 3, 2021

Particle physics theoretical and experimental studiesPhysics and Astronomy229 references39 citations

TL;DR

This paper presents a global fit of Dirac dark matter via effective field theory (EFT) using 14 dimension-6 and dimension-7 operators coupling a gauge-singlet Dirac fermion to quarks, gluons, and photons. Using the GAMBIT framework, it performs a simultaneous likelihood analysis of direct/indirect detection, LHC data, and CMB constraints, finding viable parameter space for WIMPs at new physics scales near 1 TeV despite tensions from LHC excesses and EFT validity constraints, particularly below 100 GeV DM mass.

ABSTRACT

We assess the status of a wide class of WIMP dark matter (DM) models in light of the latest experimental results using the global fitting framework $ extsf{GAMBIT}$. We perform a global analysis of effective field theory (EFT) operators describing the interactions between a gauge-singlet Dirac fermion and the Standard Model quarks, the gluons and the photon. In this bottom-up approach, we simultaneously vary the coefficients of 14 such operators up to dimension 7, along with the DM mass, the scale of new physics and several nuisance parameters. Our likelihood functions include the latest data from $\mathit{Planck}$, direct and indirect detection experiments, and the LHC. For DM masses below 100 GeV, we find that it is impossible to satisfy all constraints simultaneously while maintaining EFT validity at LHC energies. For new physics scales around 1 TeV, our results are influenced by several small excesses in the LHC data and depend on the prescription that we adopt to ensure EFT validity. Furthermore, we find large regions of viable parameter space where the EFT is valid and the relic density can be reproduced, implying that WIMPs can still account for the DM of the universe while being consistent with the latest data.

Motivation & Objective

• To assess the viability of a broad class of Dirac dark matter models using a global EFT framework.
• To simultaneously constrain 14 higher-dimensional operators coupling Dirac DM to SM quarks, gluons, and photons.
• To evaluate the consistency of WIMP models with the latest direct and indirect detection data, LHC results, and CMB observations.
• To determine the scale of new physics consistent with relic density and experimental constraints, especially below 100 GeV DM mass.
• To investigate the impact of EFT validity conditions and LHC likelihood prescriptions on global parameter fits.

Proposed method

• Utilizes the GAMBIT global fitting framework to perform a Bayesian global analysis of 14 EFT operators up to dimension 7.
• Simultaneously varies DM mass, new physics scale, and 14 operator coefficients, along with nuisance parameters.
• Incorporates likelihoods from Planck CMB data, direct detection (LUX, XENON1T), indirect detection (Fermi-LAT), and LHC searches (ATLAS/CMS).
• Applies EFT validity conditions based on energy scales and operator dimension, with a capped likelihood to enforce validity at LHC energies.
• Uses micrOMEGAs and CalcHEP within GAMBIT for relic density, direct detection rates, and indirect detection via the Process Catalogue.
• Employs UFO-to-Model conversion tools (ufo_to_mdl) to translate FeynRules models into CalcHEP-compatible format for collider simulations.

Experimental results

Research questions

• RQ1 Can Dirac dark matter models with 14 EFT operators remain viable when confronted with the full suite of cosmological and collider constraints?
• RQ2 What is the minimum new physics scale consistent with EFT validity and observed dark matter relic density below 100 GeV DM mass?
• RQ3 How do small excesses in LHC data influence the global fit results for WIMP-like dark matter?
• RQ4 To what extent do interference effects between multiple EFT operators relax relic density constraints compared to single-operator analyses?
• RQ5 How sensitive are the results to the choice of EFT validity prescription and LHC likelihood treatment?

Key findings

• For DM masses below 100 GeV, it is impossible to satisfy all experimental constraints simultaneously while maintaining EFT validity at LHC energies.
• At new physics scales around 1 TeV, the results are sensitive to small excesses in LHC data and depend on the EFT validity prescription used.
• Large regions of viable parameter space exist where the EFT remains valid and the observed relic density is reproduced, supporting the viability of WIMPs.
• Interference between multiple operators plays a significant role in relaxing relic density constraints, especially when multiple operators contribute to annihilation.
• The inclusion of collider constraints—particularly from LHC—significantly reduces viable parameter space compared to analyses neglecting LHC data.
• The use of a capped LHC likelihood improves EFT consistency but leads to different posterior distributions compared to the full likelihood, highlighting the importance of EFT validity treatment.