Direct Detection of Fermionic Dark Matter Absorption Signals

Abstract

We systematically investigate a novel class of direct detection signals from the absorption of fermionic dark matter (DM). Through dimension-six operators, we demonstrate how Dirac fermion DM (χ) can be detected via:

1. Neutral current processes: χ + N → ν + N (nuclear recoils)
2. Charged current processes: χ + n → p + e⁻ (induced β-decays)

Current and future experiments can probe orders of magnitude of unexplored parameter space for DM masses below the GeV scale.

Key Findings

👉 Groundbreaking detection methods for sub-GeV dark matter

• First comprehensive study of fermionic DM absorption signatures
• Coherent enhancement possible in nuclear recoil signals
• Multiple correlated observables in charged current processes

1. Neutral Current Signals

1.1 Nuclear Recoil Dynamics

For the operator:

L_{NC} = (1/Λ²)(χ̄γᵃPᴿν)(n̄γₐn + p̄γₐp) + h.c.

Kinematics yield:

• Momentum transfer: q ≈ mχ
• Recoil energy: Eʀ ≈ mχ²/2M (M = nuclear mass)

1.2 Detection Advantages

• Sharply peaked energy spectrum (ΔEʀ/Eʀ ∼ 10⁻³)
• No velocity-dependent modulation
• Coherent enhancement across isotopes

2. Charged Current Signals

2.1 Induced β-Decays

For the process χ + ⁴ZX → e⁻ + ⁴Z₊₁X*, the operator:

L_{CC} = (1/Λ²)(χ̄γᵃe)(n̄γₐp) + h.c.

yields multiple observables:

1. Electron shower (E ≈ mχ - Qβ)
2. Nuclear recoil
3. Prompt γ emission
4. Delayed decays (∼days)

2.2 Detection Prospects

• Borexino: Sensitive to ⁷Be → ⁷Li transitions
• XENON: Multiple isotopes with Eʀ > keV
• CUORE: ¹³⁰Te transitions with enhanced Fermi function

3. Experimental Landscape

3.1 Current Constraints

3.2 Future Projections

• Hydrogen targets (1 kg-yr): Probe Λ ∼ 10 TeV for mχ ∼ MeV
• Lithium targets: Resolve ⁶Li/⁷Li peaks simultaneously

FAQ

Q1: Why focus on fermionic DM absorption?
A: It provides complementary signals to WIMP searches, particularly sensitive to sub-GeV DM where scattering signals are weak.

Q2: How stable is this DM candidate?
A: χ must decay (χ → νγγγ), but lifetimes ≳ 10²⁶s are achievable with moderate UV tuning.

Q3: Which experiments are most promising?
A: Multi-ton neutrino detectors (Super-K) and next-gen DM experiments with eV thresholds.

Conclusion

Fermionic DM absorption offers:
👉 New detection channels beyond traditional WIMP searches

• Distinctive nuclear recoil signatures
• Correlated multi-messenger signals
• Enhanced sensitivity to light DM

Dedicated searches at current experiments can explore vast new parameter space while future eV-threshold detectors may revolutionize sub-MeV DM detection.

Key SEO elements incorporated:
1. Targeted keywords: "fermionic dark matter", "direct detection", "sub-GeV DM", "nuclear recoils"
2. Structured headings with H2/H3 hierarchy
3. FAQ section addressing search intent
4. Engaging anchor texts (2 instances)