Particle Dark Matter Parameter Fits

A major collaboration in a presentation at a dark matter conference rules out Dirac fermion dark matter for all dark matter particle masses below 100 GeV, even after considering only some of the relevant constraints on that parameter space. 

It doesn't rule out Dirac fermion dark matter at higher masses, but this parameter space is much more heavily constrained than the paper suggests due to an absence of quantum effects present in warm dark matter theories, fuzzy dark matter theories, and axion-like particle theories, due to galaxy scale dynamics, and due to microlensing limitations, among other considerations.

This said, their analysis isn't terribly convincing because it seems to be actually limited to thermal freeze out dark matter and because it doesn't adequately account for dark matter that has no non-gravitational cross-section with ordinary matter that also doesn't annihilate. A dark matter candidate of this kind evades all six of the parameters considered and is basically the paradigmatic case of a LambdaCDM dark matter particle.

The chart below compares the new physics scale Lambda and the dark matter particle mass m(χ).

In this proceeding, we present results from a global fit of Dirac fermion dark matter (DM) effective field theory (EFT) based on arXiv:2106.02056 using the GAMBIT framework. Here we show results only for the dimension-6 operators that describe the interactions between a gauge-singlet Dirac fermion and Standard Model quarks. Our global fit combines the latest constraints from Planck, direct and indirect DM detection, and the LHC. For DM mass below 100 GeV, it is impossible to simultaneously satisfy all constraints while maintaining the EFT validity at high energies. For higher masses, however, large regions of parameter space remain viable where the EFT is valid and saturates the observed DM abundance.

Ankit Beniwal (on behalf of the GAMBIT Collaboration), "Global Fits of Dirac Dark Matter Effective Field Theories" arXiv:2210.12172 (October 21, 2022) (Contribution to the proceeding of 14th International Conference on Identification of Dark Matter, Vienna, Austria (18-22 July, 2022). Submitted to SciPost Physics Proceedings).

The constraints considered are as follows:

1. Direct detection: The Wilson coefficients are evaluated at µ = 2 GeV using DirectDM and matched onto a set of non-relativistic EFT operators. These are used in DDCalc v2.2.0 to compute predicted events rates and corresponding likelihoods for XENON1T, LUX (2016), PandaX (2016) and (2017), CDMSlite, CRESST-II and CRESST-III, PICO-60 (2017) and (2019), and DarkSide-50 experiments. 

2. Relic density: Using CalcHEP v3.6.27, GUM and DarkSUSY v6.2.2, we compute the DM relic density via a thermal freeze-out scenario. Both cases where χ makes up all ( fχ ≡ Ωχ/0.12 ≈ 1) or a sub-component ( fχ ≤ 1) of the total DM abundance are studied. 

3. Fermi-LAT searches for gamma rays: Observations of dwarf spheroidal galaxies of the Milky Way place strong constraints on the DM annihilation rate. Using Fermi-LAT searches for gamma rays from DM annihilation in dwarfs, we use the gamLike v1.0.1 package within DarkBit to compute the resulting likelihood function. 

4. Solar capture: Neutrinos from DM annihilation in the Sun can be detected at the IceCube experiment. Using Capt’n General, we compute the DM capture rate in the Sun and utilise the nulike package to obtain an event-by-event level likelihood for the 79-string IceCube data.

5. Energy injection bounds: Using the CosmoBit  module of GAMBIT, we compute bounds on our model based on predicted rates of DM annihilation in the early universe. These annihilations lead to energy injection and observable effects in the cosmic microwave background. 

6. ATLAS and CMS monojet searches: By combining the ColliderBit module of GAMBIT with FeynRules v2.0, MadGraph_aMC@NLO v2.6.6, Pythia v8.1 and Delphes v3.4.2, we compute a likelihood based on monojet searches performed at the ATLAS and CMS experiments.