Multiple Gamma Lines from Semi-Annihilation (FDE, McCullough, Thaler; 1210.7817) Francesco D’Eramo 31 October 2012, GGI
Dark Matter Annihilation Annihilation χ ˜ χ → φ SM φ SM ˜ Annihilation reactions: ˜ φ SM - thermal production of relic χ particles in the early universe - high-energy cosmic rays looked for in indirect detection φ SM ˜ χ ˜ : dark matter particle χ φ SM : Standard Model (SM) field or portal to SM
Dark Matter Semi-annihilation Annihilation Semi-annihilation χ ˜ χ → φ SM φ SM χ ˜ χ → ˜ χ φ SM ˜ ˜ ˜ ˜ ˜ φ SM χ χ χ ˜ ˜ χ χ φ SM ˜ χ φ SM φ SM ˜ ˜ χ χ ˜ : dark matter particle χ φ SM : Standard Model (SM) field or portal to SM
Dark Matter Semi-annihilation time Semi-annihilation in the Early Universe ˜ ˜ χ χ Thermal abundance of dark matter Early Universe dramatically affected by the φ SM ˜ χ presence of semi-annihilations FDE, Thaler; arXiv:1003.5912 Correct relic abundance for SM singlets via ``assimilation’’ (semi-annihilation with matter/antimatter asymmetry) FDE, Fei, Thaler; arXiv:1111.5615 Today
Dark Matter Semi-annihilation time Semi-annihilation in the Early Universe ˜ ˜ χ χ Thermal abundance of dark matter Early Universe dramatically affected by the φ SM ˜ χ presence of semi-annihilations TODAY FDE, Thaler; arXiv:1003.5912 Correct relic abundance for SM singlets via ``assimilation’’ (semi-annihilation with matter/antimatter asymmetry) FDE, Fei, Thaler; arXiv:1111.5615 Gamma rays from semi-annihilation ˜ ˜ χ χ Additional channels to produce Today gamma lines with enhanced rates ˜ γ χ (FDE, McCullough, Thaler; 1210.7817)
Tentative 130 GeV Fermi gamma line Improved search for gamma ray lines in the FERMI data Energy between 20 and 300 GeV , 43 months of data and a new data-driven technique Weniger, arXiv:1204.2797; Su, Finkbeiner arXiv:1206.1616 and arXiv:1207.7060 Gamma-ray line feature in the data χ ' 130 GeV m ˜ χ ˜ ˜ χ → γγ h σ v i ' 1 . 3 ⇥ 10 − 27 cm 3 s − 1 Enhanced annihilation rate thermal freeze-out ≫ Rate only 1/30 the Typical suppression by one expected from loop factor and α EM2 one would expect DM community eagerly awaits an independent analysis by the Fermi collaboration
Outline Gamma lines from semi-annihilation A simple model for the 130 GeV Fermi line: - Hidden Vector Dark Matter
Outline Gamma lines from semi-annihilation A simple model for the 130 GeV Fermi line: - Hidden Vector Dark Matter
How are they possible? First condition χ i ˜ χ j → ˜ χ k φ SM ˜ Forbidden if Dark Matter stabilized by Z 2 symmetry Stabilization symmetry must allow semi-annihilations Second condition ⇒ ? χ i ˜ χ j → ˜ χ j φ SM χ i → ˜ χ j ˜ χ j φ SM ˜ ˜ Dark Matter particles mutually stables as long as their masses satisfy the triangle inequality m j m i m j m i m k m k
Models with semi-annihilations QCD without weak interactions γ n → π + π 0 ” p, n, π ± “ p ¯ π 0 are stable p γ π 0 m n m π π + is unstable ¯ n m p Semi-annihilations generically present in multi-component models with ``flavor’’ and/or ``baryon’’ symmetries and in many other models Agashe et al., hep-ph/0403143, hep-ph/0411254 and arXiv:1012.4460 Hambye et al., arXiv:0811.0172, arXiv:0907.1007 and arXiv:0912.4496; FDE, Thaler, arXiv:1003.5912 Batell et al., arXiv:1007.0045 and arXiv:1105.1781; Bélanger et al., arxiv:1202.2962; Aoki et al., arxiv:1207.3318
Gamma lines from semi-annihilation ˜ ˜ ˜ χ γ χ χ VS γ ˜ ˜ γ χ χ SPECTRA ENRICHED BOOSTED DM Additional channels to produce Semi-annihilations today produce monochromatic photons boosted dark matter particles
Gamma lines from semi-annihilation ˜ ˜ ˜ χ γ χ χ VS γ ˜ ˜ γ χ χ SPECTRA ENRICHED Additional channels to produce monochromatic photons BOOSTED DM how can we detect them??? Semi-annihilations today produce boosted dark matter particles
General features - I χ i ˜ ˜ χ j → ˜ χ k γ Parametrically larger cross sections γ ψ j ψ k ψ i g i g j g k e g i g i e e ψ i ψ i γ γ
General features - I χ i ˜ ˜ χ j → ˜ χ k γ Parametrically larger cross sections γ ψ j ψ k ψ i ψ i → γγ / α 2 EM α 2 h σ v i ψ i ¯ i g i g j g k e g i g i e e h σ v i ψ i ψ j → ψ k γ / α EM α i α j α k ψ i ψ i γ γ Annihilation suppressed by α EM2 , Fermi line challenging Semi-annihilation just by α EM , modest enhancement
General features - II χ i ˜ ˜ χ j → ˜ χ k γ Gamma ray spectrum from semi-annihilations Monochromatic lines, = ( m i + m j + m k )( m i + m j − m k ) E ij → k one for each (i,j,k) γ 2( m i + m j ) Lines with different d Φ γ X N ij → k E γ � E ij → k � � / n i n j h σ v i ij → k δ γ γ intensities dE γ ij → k Dark sector with N(N-1)(N-2)/2 gamma lines N DM species from semi-annihilations
General features - III χ i ˜ ˜ χ j → ˜ χ k γ Accompanying annihilation signal Line at E ij->k should have three companion χ i ¯ ˜ ˜ χ i → γγ (weaker) lines at E i =m i , E j =m j and E k =m k General dark sector: Simplest dark sector (i=j=k=1): - N lines from annihilations - line at 130 GeV (semi-annihilation) - N(N-1)(N-2)/2 gamma lines - line at 173 GeV (annihilation, weaker) from semi-annihilations Smoking gun signature of semi-annihilation: line at 173 GeV
General features - IV χ i ˜ ˜ χ j → ˜ χ k γ Wide range of DM masses m DM = 130 GeV Annihilation: gamma line at 130 GeV m DM = ??? Semi-annihilation: gamma line at 130 GeV A signal at 130 GeV could arise from a wide range of DM masses (allows common DM explanation of Fermi line and positron excess) Fermi data fit performed ⇣ m i m j ⌘ 2 1 . 3 ⇥ 10 − 27 cm 3 s − 1 h σ v i ij → k = at fixed DM density 130 GeV
General features - V χ i ˜ ˜ χ j → ˜ χ k γ Generic absence of a 112 GeV line Annihilation: both γγ and γ Z final state, also line at 112 GeV Semi-annihilation: correspondent process is χχ -> χ Z (no photon) Still possible to have an ‘accidental’ 112 GeV line but not a robust prediction of semi-annihilation framework
Direct Detection and Collider Annihilation: prediction for direct detection and collider rates ˜ ˜ χ χ ˜ ˜ χ χ φ SM φ SM ˜ ˜ φ SM φ SM χ χ φ SM φ SM Semi-annihilation: more model dependent ˜ ˜ - Direct detection: through DM loops χ χ - Collider: three DM particles in the final state ˜ φ SM χ Rates typically suppressed compared to corresponding annihilation scenario
Outline Gamma lines from semi-annihilation A simple model for the 130 GeV Fermi line: - Hidden Vector Dark Matter
Hidden Vector Dark Matter (HVDM) Dark group SM EW group Decoupled but just for this G d SU (2) L × U (1) Y slide... G d completely broken U (1) em G d = SU(2) in Hambye et al., arXiv:0811.0172, arXiv:0907.1007 and arXiv:0912.4496 Spin-1 Dark Matter - DM: massive gauge bosons of a spontaneously broken G d - Custodial symmetry: degenerate DM with mass m V = 173 GeV ◆ 2 ✓ 173 - Cross section for the Fermi line: h σ v i ref ' 2 . 3 ⇥ 10 − 27 cm 3 s − 1 h σ v i = 130
Messenger fields Dark group SM EW group Vector-like fermions ψ charged under G d SU (2) L × U (1) Y both gauge groups G d completely broken U (1) em Messenger Mass m M - Dark matter stability: m V < 2 m M - No DM annihilation into fermion pairs (diffuse photon): m V < m M - m M not too large if we account for the Fermi line (next slides)
Gamma rays from box diagrams - I γ V i E ann = 173 GeV g i t i e γ h σ v rel i V V → γγ / α 2 EM α 2 g i t i e d V i γ V j V k E semi = 130 GeV γ g j t j g k t k 1 2 h σ v rel i V V → V γ / α EM α 3 d g i t i e Parametrically enhanced! γ V i
Gamma rays from box diagrams - II An explicit case: G d = SU(3) ◆ 8 ✓ ◆ 6 h σ v rel i V V → γγ = 3 . 0 ⇥ 10 − 29 cm 3 s − 1 ⇣ α d ✓ 200 GeV ⌘ 2 M V N 2 f 3 . 55 173 GeV M M ◆ 8 ✓ ◆ 6 2 h σ v rel i V V → V γ = 2 . 3 ⇥ 10 − 27 cm 3 s − 1 ⇣ α d ✓ 200 GeV 1 ⌘ 3 M V N 2 f 3 . 55 173 GeV M M 14 Large couplings M V = 173 GeV 2.3 ¥ 10 - 26 cm 3 ê s 12 (but still perturbative α d < 4 π ) 10 8 a d 6 2.3 ¥ 10 - 27 cm 3 ê s Light messengers 4 Ê 2.3 ¥ 10 - 28 cm 3 ê s 2 m M < 300 GeV 0 200 220 240 260 280 300 M M @ GeV D
Constraints on messengers Messengers ψ : fermions with mass 200 - 300 GeV ψ ∈ ( 3 , 0 ) SM - Splitting between charged and neutral: M± - M0 ≈ 100 MeV - Neutral component stable, 1/100 of total DM Cirelli et al., hep-ph/0512090 Direct detection Collider constraints Pair-production of charged ψ Spin-dependent only at one-loop (similar to nearly pure-wino) Consistent once combined with Consistent with LHC searches the low-density ATLAS, arXiv:1202.4847
A freeze-out scenario for HVDM - I Dark group Messengers ψ SM EW group G d SU (2) L × U (1) Y Dark Higgs mixing SM Higgs H Bosons Φ G d completely broken U (1) em Freeze-out through the Higgs portal Dark gauge group broken by three SU(3) fundamental scalars 8 ◆ 2 ✓ 1 + sin θ h h 1 X L ⊃ λ mix | Φ | 2 | H | 2 2 M 2 V A iµ A i + ... ⇒ µ v d i =1
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