Multi-messenger FIMP

TL;DR

The paper develops a model-independent EFT framework for leptophilic FIMP dark matter produced via UV freeze-in during a low-temperature reheating era governed by a monomial inflaton potential. It demonstrates multi-messenger prospects by linking DM relic abundance, EFT cutoffs, and reheating dynamics to signals across direct detection (DM–electron scattering), indirect detection (lepton and neutrino channels), collider searches (mono-photon + MET at future $e^+e^-$ colliders), and inflationary gravitational waves. A key finding is that bosonic reheating with $n=4$ or $n=6$ can yield EFT-viable temperatures and DM masses while producing detectable GW spectra, providing complementary probes to colliders and direct/indirect searches. The study highlights the potential of future GW detectors to explore broader regions of the $_{ m NP}-m_{ m DM}$ parameter space, enabling a true multi-messenger approach to FIMP DM and early-Universe reheating physics.

Abstract

We propose a multi-messenger frontier probe of non-thermal or freeze-in massive particle (FIMP) dark matter (DM) by considering an effective field theory (EFT) setup. Assuming leptophilic operators connecting DM with the standard model (SM) bath, we consider DM mass ($m_{\rm DM}$) and the reheat temperature of the Universe ($T_{\rm rh}$) in a regime which prevents DM-SM thermalisation. Low $T_{\rm rh}$ allows sizeable DM-SM interactions even for non-thermal DM allowing the latter to be probed at direct, indirect detection frontiers as well as future electron-positron and muon colliders. An extended reheating period governed by monomial inflaton potential after its slow-roll phase not only generates the required abundance of non-thermal DM via ultraviolet (UV) freeze-in but also brings the scale-invariant primordial gravitational waves (GW) within reach of near future experiments across a wide range of frequencies. While particle physics experiments can probe $T_{\rm rh} \sim O(10)$ GeV and FIMP DM with mass $m_{\rm DM} \sim O(1)$ TeV, future GW detectors are sensitive to a much wider parameter space.

Figures (16)

• Figure 1: The blue and black lines, shown as thick ($n=4$) and dashed ($n=6$), represent the bosonic and fermionic reheating scenarios, respectively. The thick gray line, common for both bosonic and fermionic reheating, corresponds to the $n=2$ scenario. The dark gray shaded region is excluded by BBN constraints. The parameters $\mu_{\rm eff}$, $y_{\rm eff}$ and $m_{\phi}(a_{\rm rh})$ are fixed by values of $n$ and $T_{\rm rh}$ for a particular number of e-fold during inflation. For example, for $T_{\rm rh}= 1$ GeV, $n=2$ gives $\mu_{\rm eff} \simeq 2.5\times10^{-2}$ GeV, $y_{\rm eff} \simeq 1.6\times10^{-15}$ and $m_{\phi}(a_{\rm rh}) \simeq 1.5\times 10^{13}$ GeV. For the same reheating temperature, $n=6$ gives $\mu_{\rm eff} \simeq 2.1\times10^{-12}$ GeV, $y_{\rm eff} \simeq 2.0\times 10^{-5}$ and $m_{\phi}(a_{\rm rh}) \simeq 1.1\times 10^{-7}$ GeV. Here we fix the number of e-folds during inflation to $55$.
• Figure 2: The different colored lines correspond to various choices of reheating temperature $(T_{\text{rh}})$ and $n=4~(6)$ shown by solid (dashed) lines. The analysis assumes a bosonic reheating scenario, while all other parameters are fixed at $c^{}_{\text{L}\chi}=c^{}_{\text{R}\chi}=1.0$ for scalar DM (left) and $c^{}_{\text{L}\Phi}=c^{}_{\text{R}\Phi}=1.0$ for fermionic DM (right) with $m_{\rm DM}=500~\rm MeV$ and $\Lambda_{\rm NP}=2.0~\rm TeV$.
• Figure 3: Feynman diagrams are related to the Direct (left) and Indirect (right) detection of the complex scalar ($\Phi$) and fermionic ($\chi$) DM, where $\ell$ denotes SM leptons.
• Figure 4: The shaded region indicates areas excluded by the direct detection, while the thick solid (dashed) boundary shows current (future) constraints (sensitivities) on DM detection. We consider $c^{}_{\text{L}\chi}=c^{}_{\text{R}\chi}=1.0$ for scalar DM (left) and $c^{}_{\text{L}\Phi}=c^{}_{\text{R}\Phi}=1.0$ for fermionic DM (right).
• Figure 5: The shaded region indicates areas excluded by the indirect detection, while the thick solid (dashed) boundary shows current (future) constraints (sensitivities) on DM annihilation. DM annihilation into a neutrino pair could also be constrained by the Hyper-Kamiokande neutrino experiment, for low $m_{\rm DM}$. For this we choose $c^{}_{\text{L}\chi}=c^{}_{\text{R}\chi}=1.0$ for scalar DM (left) and $c^{}_{\text{L}\Phi}=c^{}_{\text{R}\Phi}=1.0$ for fermionic DM (right).