Collider and CMB complementarity of leptophilic dark matter with light Dirac neutrinos

TL;DR

The paper investigates leptophilic dark matter interacting with light Dirac neutrinos through a dim-6 EFT, focusing on thermal relic production, mono-$\gamma$ collider signatures at future lepton colliders, and the cosmological imprint on $N_{\rm eff}$. By scanning DM mass $m_\chi$ and cutoff $\Lambda$ across various operator classes that couple DM, SM leptons, and $\nu_R$, it shows how collider searches and cosmological bounds complement each other, with some operator choices yielding enhanced $N_{\rm eff}$ detectable by upcoming CMB experiments. The work demonstrates that collider probes can reach $\Lambda$ up to several TeV (and in some cases tens of TeV) for $m_\chi$ in the TeV range, while future CMB surveys (CMB-S4, CMB-HD) can test nearly the entire viable parameter space, highlighting a powerful collider–cosmology synergy. It also discusses plausible UV completions that realize the EFT operators and notes that neutrinoless double beta decay could falsify the pure Dirac-neutrino assumption, making the scenario testable across multiple experimental fronts.

Abstract

We study the discovery prospects of leptophilic dark matter (DM) in future lepton colliders by considering the light neutrinos to be of Dirac type. Adopting an effective field theory (EFT) approach, we write down dimension six operators connecting the standard model (SM) fields, light Dirac neutrinos and DM. Considering DM relic to be generated via the thermal freeze-out, we check the discovery prospects at future lepton colliders via mono-photon plus missing energy searches. The right chiral parts of light Dirac neutrinos get thermalised due to their interactions with the bath as well as leptophilic DM, leading to enhanced effective relativistic degrees of freedom $N_{\rm eff}$ within reach of future cosmic microwave background (CMB) experiments. The interplay of existing bounds from cosmological observations related to DM relic and $N_{\rm eff}$, direct and indirect detection of DM, astrophysics and collider observations leave promising discovery prospects at future electron and muon colliders along with complementary signatures at future CMB experiments.

Figures (16)

• Figure 1: Left panel: DM yield variation with $x=m_{\chi}/T$ with $m_{\chi}=260$ GeV and $\Lambda=2500$ GeV. Right panel: Relic allowed parameter space in $\Lambda-m_{\chi}$ plane.
• Figure 2: 1-loop Feynman diagrams from DM-nucleon scattering. Left: DMEFT contribution; right: $\nu$DMEFT contribution.
• Figure 3: Spin-independent DM-nucleon cross-section for relic density allowed parameter space denoted by red (DMEFT) and blue (DMEFT+$\nu$DMEFT) contours. Dark gray (light gray) shaded region is excluded by LZ experiment bound published in 2022 LZ:2022lsv (2024 LZ:2024) in $\sigma_{\chi N}-m_{\chi}$ plane.
• Figure 4: Relic allowed parameter space in $\left\langle \sigma v \right\rangle-m_{\chi}$ plane denoted by red (DMEFT) and blue (DMEFT+$\nu$DMEFT) contours. Gray shaded region is excluded from combined data analysis of MAGIC Cherenkov telescopes and Fermi-LAT experiment Fermi-LAT:2016afa in $\left\langle \sigma v \right\rangle_{\chi \chi \rightarrow \tau^+ \tau^-}$ versus $m_{\chi}$ plane.
• Figure 5: Feynmann diagram of mono-$\gamma$+ missing energy ($\slashed{E}$) for DM signal at the the $e^+e^-$ colliders.