Could a � line betray the mass of Light Dark Matter? C. Boehm, J. Orloff, P. Salati Cern, Clermont, Annecy astro-ph/0607437 Light Dark Matter to ��
Outline • Why Dark Matter? Why not Light DM? • 511 keV signal from Galactic Center: Why LDM? • Cross check: monochromatic � line at m dm • Detectability Light Dark Matter to �� J. Orloff 2
Why Dark Matter? Light Dark Matter to �� J. Orloff 3
Why Dark Matter? Short: (googling Dark Matter 2007) ask Meryl Streep! Light Dark Matter to �� J. Orloff 3
Why Dark Matter? Short: (googling Dark Matter 2007) ask Meryl Streep! Light Dark Matter to �� Li ht Dark Matter J. Orloff f 3
Why Dark Matter? Short: (googling Dark Matter 2007) ask Meryl Streep! Light Dark Matter to �� Li ht Dark Matter J. Orloff f 3
Why Dark Matter? Light Dark Matter to �� J. Orloff 4
Why Dark Matter? • Need Cold DM with Ω DM = 0 . 24 on all scales: Light Dark Matter to �� J. Orloff 4
Why Dark Matter? • Need Cold DM with Ω DM = 0 . 24 on all scales: DM halo • Galaxies’ flat rotation curves Light Dark Matter to �� J. Orloff 4
Why Dark Matter? • Need Cold DM with Ω DM = 0 . 24 on all scales: DM halo • Galaxies’ flat rotation curves • Clusters’ temp. distributions & collisions Clowe et al. 2006 Cold dark lensing matter X gas “Bullet” cluster 1E 0657-56 Light Dark Matter to �� J. Orloff 4
Why Dark Matter? • Need Cold DM with Ω DM = 0 . 24 on all scales: DM halo • Galaxies’ flat rotation curves • Clusters’ temp. distributions & collisions • Structure formation and CMB WMAP astro-ph/0603449 Light Dark Matter to �� Light Dark Matter to �� J. Orloff 4 4
Why Dark Matter? • Need Cold DM with Ω DM = 0 . 24 on all scales: DM halo • Galaxies’ flat rotation curves • Clusters’ temp. distributions & collisions • Structure formation and CMB • Nucleosynthesis + CMB: Ω b = 0 . 04 ≪ Ω DM ⇒ DM is non-baryonic DM i b WMAP astro-ph/0603449 Light Dark Matter to �� Light Dark Matter to �� J. Orloff 4 4
Why Dark Matter? • Need Cold DM with Ω DM = 0 . 24 on all scales: DM halo • Galaxies’ flat rotation curves • Clusters’ temp. distributions & collisions • Structure formation and CMB • Nucleosynthesis + CMB: Ω b = 0 . 04 ≪ Ω DM ⇒ DM is non-baryonic DM i b WMAP astro-ph/0603449 • DM particle: major phenomenological nomenol ogical excuse for physics BSM! ! (since � DM Direct Detection excl. & � oscill.) n excl. & � � oscill.) ⇒ “vanilla” SUSY DM Light Dark Matter to �� Light Dark Matter to �� J. Orloff 4 4
Why Dark Matter? • Need Cold DM with Ω DM = 0 . 24 on all scales: DM halo • Galaxies’ flat rotation curves • Clusters’ temp. distributions & collisions • Structure formation and CMB • Nucleosynthesis + CMB: Ω b = 0 . 04 ≪ Ω DM ⇒ DM is non-baryonic DM i b WMAP astro-ph/0603449 • DM particle: major phenomenological nomenol ogical excuse for physics BSM! ! (since � DM Direct Detection excl. & � oscill.) n excl. & � � oscill.) ⇒ “vanilla” SUSY DM • Gravity modifications? Even less conservative! (& contrived) Light Dark Matter to �� Light Dark Matter to �� J. Orloff 4 4
Why not Light DM? • Honest poll in this room: “Who would order new MeV particles?” • More serious: Lee-Weinberg bound ? Ω dm < 1 ⇒ m dm > 2GeV σ ann v ∼ m 2 dm G 2 Only holds for weak-like cross-sections: F ( ∼ 1 / Ω) • For other behaviors or G F , relic density can be OK for scalar DM with: • m dm > 1MeV (otherwise nucleosynthesis problems) • m dm < 100 MeV (otherwise unseen � ’s from � 0 ) • Involves light gauge boson U , or mirror fermions F , or both dm e v dm e 2 U F and/or v 2 dm dm e e σv ∼ v 2 q 2 Udm q 2 Ue m 2 dm /m 4 dm m e U σv ∼ C 4 m − 2 F ⇒ Intriguing possibility (Boehm, Fayet hep-ph/0305261) Light Dark Matter to �� J. Orloff 5
511 keV � ‘s from Galactic Center 10 -4 10 -3 10 -2 photons/cm 2 /s/sr Nothing in the ---- ---- galactic disk!!! 5°= 1kpc = galactic bulge SPI/INTEGRAL, 2003-2005 • 1.6 10 -3 photons/cm 2 /s from the bulge, with energy 511 ± 1 keV • ⇒ positronium at rest annihilating into 2 photons Light Dark Matter to �� J. Orloff 6
Are these e + “Dark”? “Found a 0.5 MeV radiation excess? Do your Nuclear Physics right!” However: • All known potential astrophysical sources (e.g. hypernovae) more frequent in the disk than in the (quiescent, old stars) bulge. • Known e + sources also have known intense gamma lines (unseen) • Diffuse steady signal requires at least 8(?) steady(?) point sources On the other hand, the DM density • must increase in the bulge, and would give a steady, diffuse signal • fits a reasonable profile: (Ascasibar a-ph/0507142) ρ NF W ( r ) ∼ 1 /r • requires both mirror fermions F (e + signal) σv ∼ C 4 m − 2 F σv ∼ v 2 q 2 Udm q 2 Ue m 2 dm /m 4 and U boson (relic density too large otherwise) U ⎧ m F > 100GeV ⎨ with: m dm ∼ 1 → 100MeV < m U q dmU q eU ∼ 10 − 6 (for m U ∼ m dm ) ⎩ Light Dark Matter to �� J. Orloff 7
Light DM Window • Upper limits on m dm : φ γ cont ( dm + dm → e + e − γ ) > φ obs. ( . 5 → 5 MeV ) • FSR: � m dm < 20 MeV (Beacom, a-ph/0409403) or m dm < 35 MeV w. better cross-section (Boehm, hep-ph/0606058) • In flight annihilation: some e + can annihilate before stopping and exceed • error bars (???) on continuum � m dm < 3MeV (Beacom, a-ph/0512411) , • continuum itself � m dm < 20MeV • Lower limits on m dm : • Nucleosynthesis disturbed by annihilation � m dm > 2MeV (Serpico, Raffelt, a-ph/0403417) • Neutrinos from SN1987A too cold (Fayet, Sigl, hep-ph/0602169) � m dm > 10MeV if it couples to neutrinos (not necessary) ⇒ 2MeV < m dm < 20 MeV Light Dark Matter to �� J. Orloff 8
The story so far • There is an intense positronium annihilation line from galactic center • No easy astrophysical explanation • ⇒ Imagine annihilation: LDM+LDM � e + e - • Produced positrons radiate energy locally (in 1pc) , then (most) find an e - to form positronium and annihilate (25%) into 511 keV gammas. Requires peculiar particle models, with special ingredient/parameters: what would it take to convince (and believe) this is the real story? If DM annihilation produces many e + e - pairs, it must guarantee a minimum number of unambiguous monochromatic �’s ⇒ how much? ⇔ Is there a chance of proving this scenario? Light Dark Matter to �� J. Orloff 9
⇒ X-check: e + e - production • For heavy m F >>m dm,e , L = ¯ ψ F ( c R P L + c L P R ) ψ e φ dm + h.c reduces to effective interaction heavy F exchange c ∗ R,L e e dm dm + O (1 /m 2 ∼ F ) F a + ibγ 5 dm e dm e m F c L,R 1 dm φ dm ¯ L eff = φ ∗ ψ e ( a + ibγ 5 ) ψ e ; a + ib = c ∗ L c R . m F β e = 2 10 − 30 � m dm � 2 a 2 β 2 e + b 2 � � c m 3 / s σ 511 v r = 4 πm 2 MeV SPI F � e /m 2 1 − m 2 β e = dm Light Dark Matter to �� J. Orloff 10
⇒ X-check: � line at m dm • 2x3 box diagrams: c ∗ c L,R c L,R R,L F e dm e dm dm F + + e e F F e F dm e dm F dm c ∗ c L,R c ∗ R,L R,L � • Each superficially but gauge invariance requires 2 d 4 k/k 4 � d 4 k/k 6 < 1 /m 2 external momenta ⇒ and 1/m F expansion OK F m F 1 = 0 , ( q 1 + q 2 ) 2 = 4 m 2 C 0 ( q 2 dm , q 2 2 = 0 , m 2 e , m 2 e , m 2 e ) e � d 4 k dm + O (1 /m 2 1 F ) = e ∼ (( k + q 1 ) 2 − m 2 e ) ( k 2 − m 2 e ) (( k − q 2 ) 2 − m 2 iπ 2 e ) • a + ibγ 5 dm � 1 1 dx e x ln(1 − x (1 − x )4 m 2 dm /m 2 m F = e − iε F ) 4 m 2 0 dm α 2 m 2 dm | 2 + a 2 | 1 + 2 C 0 ( m 2 e b 2 | 2 C 0 m 2 e − m 2 dm ) | 2 � � σ γγ v r = × (2 π ) 3 m 2 m 2 F dm Light Dark Matter to �� J. Orloff 11
X-check: � line / e + e - dm ) C 0 | 2 + b 2 | 2 m 2 α 2 m 2 a 2 | 1 + 2 ( m 2 e − m 2 dm C 0 | 2 = σ γγ η . e = 2 π 2 β e m 2 a 2 β 2 e + b 2 σ 511 dm Boehm, Orloff, Salati Boehm, Orloff, Salati b=0 η = σ γγ /σ e + e − 10 � 4 a=0 10 � 6 10 � 2 10 � 1 10 0 10 1 10 2 m dm − m e (MeV) Light Dark Matter to �� J. Orloff 12
X-check: � line / e + e - dm ) C 0 | 2 + b 2 | 2 m 2 α 2 m 2 a 2 | 1 + 2 ( m 2 e − m 2 dm C 0 | 2 = σ γγ η . e = 2 π 2 β e m 2 a 2 β 2 e + b 2 σ 511 dm • Not vanishing � guaranteed signal, given the known e + e - signal • Enhancements? • ? But dangerous for nucleosynthesis ! m dm ≈ m e ⇔ β e ≈ 0 • More heavier particles, like tau, in loop? η ( m τ ≫ m dm ) ∼ m 2 dm / ( m 2 F m 2 τ ) Not much: m 2 e /m 2 (despite prefactor) dm ⇒ will be relevant only for couplings c L,R scaling like Yukawas l f Γ e + e − ≈ α 2 m 2 Γ γγ • Kasuya (a-ph/0602296) estimate dm η K = 2 π 2 m 2 e β 3 e ( for moduli decay ): overestimates by 1000 (!!!) at 10MeV � (wrongly) concludes detectability in near future Light Dark Matter to �� J. Orloff 13
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