Neutrino Signals from Decaying Dark Matter 1 Michael Grefe Deutsches Elektronen-Synchrotron DESY, Hamburg The Dark Matter Connection: Theory and Experiment GGI Firenze – 18 May 2010 1 Based on work in collaboration with Laura Covi, Alejandro Ibarra and David Tran: JCAP 0901 (2009) 029 & JCAP 1004 (2010) 017 Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 1 / 20
Outline Motivation 1 Decaying Gravitino Dark Matter 2 Neutrino Detection 3 Neutrino Constraints on Decaying Dark Matter 4 Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 2 / 20
Motivation The Quest for Dark Matter I Cosmological Evidence Assuming standard general relativity, the existence dark matter is firmly established from gravitational observations on various scales Dark Matter Properties: • Weak-scale (or smaller) interactions • Cold (maybe warm) • Very long-lived (not necessarily stable!) Particle dark matter can be a (super)WIMP with lifetime ≫ age of the Universe! Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 3 / 20
Motivation The Quest for Dark Matter II Why are we interested in Cosmic-Ray Signatures? )) 0.3 - (e φ )+ Complementary method to direct dark matter 0.2 + (e φ searches and searches at colliders ) / ( + (e 0.1 Recent observations: φ Positron fraction • PAMELA : Steep rise in the positron fraction above 10 GeV • Fermi LAT : Hardening of the electron spectrum around 100 GeV 0.02 • H.E.S.S. : PAMELA Change of slope in the electron spectrum at 1 TeV 0.01 1 10 100 Energy (GeV) [Adriani et al. (2008)] In conflict with expectations from secondary ) -1 sr production and standard propagation models -1 + 5% s ∆ E -10% ∆ E ± 15% -2 m Could be explained by nearby astrophysical 2 dN/dE (GeV sources (pulsars are a source for e + e − -pairs) 10 2 3 E Signature of dark matter annihilation/decay? ATIC PPB-BETS Kobayashi Fermi H.E.S.S. H.E.S.S. - low-energy analysis Further observations in different cosmic-ray Systematic error Systematic error - low-energy analysis Broken power-law fit channels needed to discriminate possibilities 10 2 10 3 Energy (GeV) [Aharonian et al. (2009)] Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 4 / 20
Motivation Annihilating vs Decaying Dark Matter Why are we interested in Decaying Dark Matter? Flux from the galactic halo: Dark Matter Decay Dark Matter Annihilation dJ halo = � σ v � DM dN dJ halo dN � � 1 � l ) d � l l ) d � l ρ 2 � halo ( = ρ halo ( dE 8 π m 2 dE dE 4 π τ DM m DM dE DM l.o.s. l.o.s. particle physics astrophysics particle physics astrophysics Annihilation: 4.5 NFW decay NFW annihilation • Strong signal from peaked structures 4 Einasto decay Einasto annihilation • Enhancement of cross section needed Isothermal decay σ = S/ √ B compared to full sky 3.5 Isothermal annihilation • Best statistical significance for small cone around galactic centre 3 Decay: 2.5 • Milder angular dependence 2 • Less constrained and less studied 1.5 • Best statistical significance for full-sky 1 observation 0.5 0 Annihilating and decaying dark matter 0 30 60 90 120 150 180 cone half angle towards galactic center ( ° ) require different strategies for observation! Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 5 / 20
Decaying Gravitino Dark Matter Outline Motivation 1 Decaying Gravitino Dark Matter 2 Neutrino Detection 3 Neutrino Constraints on Decaying Dark Matter 4 Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 6 / 20
Decaying Gravitino Dark Matter Decaying Gravitino Dark Matter I Motivation from the early Universe Gravitino arises naturally as the spin-3/2 superpartner of the graviton � � m ˜ � 2 Thermal production: Ω 3 / 2 h 2 ≃ 0 . 27 � T R � � g 100 GeV m 3 / 2 10 10 GeV 1 TeV [Bolz et al. (2001)] Thermal leptogenesis: T R � 10 9 GeV ⇒ m 3 / 2 � O ( 10 ) GeV favored Correct relic density for typical leptogenesis and supergravity parameters Problem: Late gravitino decays are in conflict with BBN predictions! Gravitino LSP is a natural candidate for cold dark matter Problem: Late NLSP decays usually spoil BBN predictions! Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 7 / 20
Decaying Gravitino Dark Matter Decaying Gravitino Dark Matter I Motivation from the early Universe Gravitino arises naturally as the spin-3/2 superpartner of the graviton � � m ˜ � 2 Thermal production: Ω 3 / 2 h 2 ≃ 0 . 27 � T R � � g 100 GeV m 3 / 2 10 10 GeV 1 TeV [Bolz et al. (2001)] Thermal leptogenesis: T R � 10 9 GeV ⇒ m 3 / 2 � O ( 10 ) GeV favored Correct relic density for typical leptogenesis and supergravity parameters Problem: Late gravitino decays are in conflict with BBN predictions! Gravitino LSP is a natural candidate for cold dark matter Problem: Late NLSP decays usually spoil BBN predictions! Possible solution: R -parity not exactly conserved! Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 7 / 20
Decaying Gravitino Dark Matter Decaying Gravitino Dark Matter II Bilinear R-Parity Violation Renormalisable R-parity violating terms in the superpotential: R p = µ i L i H u + λ LLE c + λ ′ LQD c + λ ′′ U c D c D c W / Proton stability guaranteed if λ ′′ vanishes We concentrate on bilinear R-parity breaking: • µ i , λ, λ ′ related by field redefinitions • λ ′′ remains absent R p -couplings: Bounds on / R p -couplings • NLSP decays before BBN: Lower bound on / R p -couplings • Lepton/baryon asymmetry not washed out: Upper bound on / R p -couplings Gravitino couplings suppressed by the Planck mass and the small / Gravitino unstable but very long-lived: τ 3 / 2 ≈ O ( 10 23 − 10 37 ) s Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 8 / 20
Decaying Gravitino Dark Matter Decaying Gravitino Dark Matter II Bilinear R-Parity Violation Renormalisable R-parity violating terms in the superpotential: R p = µ i L i H u + λ LLE c + λ ′ LQD c + λ ′′ U c D c D c W / Proton stability guaranteed if λ ′′ vanishes We concentrate on bilinear R-parity breaking: • µ i , λ, λ ′ related by field redefinitions • λ ′′ remains absent R p -couplings: Bounds on / R p -couplings • NLSP decays before BBN: Lower bound on / R p -couplings • Lepton/baryon asymmetry not washed out: Upper bound on / R p -couplings Gravitino couplings suppressed by the Planck mass and the small / Gravitino unstable but very long-lived: τ 3 / 2 ≈ O ( 10 23 − 10 37 ) s The gravitino is a viable decaying dark matter candidate! Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 8 / 20
Decaying Gravitino Dark Matter Decaying Gravitino Dark Matter III Gravitino Decay Channels R-parity breaking treated in terms of a non-vanishing sneutrino VEV γ, Z 0 , W ± Z 0 , W ± + ψ 3 / 2 � ˜ ν l � ψ 3 / 2 � ˜ ν l � h h χ 0 , ˜ χ ∓ ˜ ν l , l ∓ ν l , l ∓ ν ∗ ˜ l + ψ 3 / 2 + ψ 3 / 2 � ˜ ν l � χ 0 ˜ ν l ν l Observable cosmic rays are created from direct production, gauge/Higgs boson fragmentation and lepton decays Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 9 / 20
Decaying Gravitino Dark Matter Decaying Gravitino Dark Matter IV Indirect Detection 10 0 Wτ Branching Ratio Z 0 ν τ 10 -1 Gravitino branching ratios: hν τ • Independent of sneutrino VEV • Dominant dependence on gravitino mass 10 -2 • Large branching ratio into a neutrino line Smoking gun signature in neutrinos! γν τ 10 -3 100 1000 m 3/2 (GeV) Gravitino parameters constrained by antiproton observations due to hadronic decays Gravitino decays cannot fit PAMELA and Fermi LAT with these parameters [Buchmüller et al. (2009)] Decaying gravitino dark matter cannot account for the PAMELA and Fermi LAT excesses without additional astrophysical sources Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 10 / 20
Neutrino Detection Outline Motivation 1 Decaying Gravitino Dark Matter 2 Neutrino Detection 3 Neutrino Constraints on Decaying Dark Matter 4 Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 11 / 20
Neutrino Detection Neutrino Flux and Atmospheric Background I Scalar Dark Matter Candidate Scalar dark matter decay channels: • DM → νν : two-body decay with monoenergetic line at E = m DM / 2 • DM → ℓ + ℓ − : soft spectrum from lepton decay (no neutrinos for e + e − ) • DM → Z 0 Z 0 / W + W − : low-energy tail from gauge boson fragmentation Triangular tail from extragalactic dark matter decays Neutrino oscillations distribute the flux equally into all neutrino flavours Atmospheric neutrinos are dominant background for TeV scale decaying DM 10 -1 DM → νν DM → µµ / ττ atmospheric neutrinos DM → ZZ/WW Super-K ν µ 10 -2 2 × dJ/dE ν (GeV cm -2 s -1 sr -1 ) Amanda-II ν µ Frejus ν e 10 -3 ν µ Frejus ν µ Amanda-II ν µ ν e IceCube-22 ν µ 10 -4 ν τ 10 -5 m DM = 1 TeV , τ DM = 10 26 s 10 -6 10 -7 E ν 10 -8 10 0 10 1 10 2 10 3 10 4 10 5 E ν (GeV) Michael Grefe (DESY Hamburg) Neutrino Signals from Decaying DM GGI Firenze – 18 May 2010 12 / 20
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