Dark Matter Models. Stephen West. and. Fellow\Lecturer. RHUL and RAL

Transcription

1 Dark Matter Models Stephen West and Fellow\Lecturer RHUL and RAL

2 Introduction Research Interests Important Experiments Dark Matter - explaining PAMELA and ATIC Some models to explain data Freeze out Sommerfeld effect Summary Outline 2

3 Research Interests BSM model building Supersymmetry Higgs Physics Neutrino Physics Flavour Physics Extra Dimensions Early Universe Cosmology Baryogenesis/Leptogenesis BBN Dark Matter

4 Dark Matter Dark matter At the LHC Astrophysics Experiments Evidence for Dark matter: Cosmological Scales: CMB power spectrum...wmap Ωh 2 dm = ± Galaxy Cluster Scales: Bullet cluster, other cluster dynamics Galactic Scales: Rotation Curves, expect velocity of stars v(r) 1/ r but measure flat rotation curves 4

5 Important Experiments Current Data: Future Data: PAMELA ( e ±,p ± ) ATIC ( e ±,p ± ) γ Hess ( ) + many more CDMS Zeplin DAMA + many more FERMI/GLAST ( γ) Icecube ( ν) LHC?... } } Indirect Detection Direct Detection 5

6 Galactic Cosmic Rays GCRs (GCRs) high-energy particles flowing into our solar system from far away in the Galaxy. Composition: protons 90% helium 9% electrons 1% + other heavier nuclei Origins: Probably accelerated in the blast waves of supernova remnants (SNRs) Particles/Nuclei bouncing back and forth in magnetic field of the remnants Some gain enough energy to escape into Galaxy and become GCRs 6

7 More GCRs Some GCRs observed with energies above max possible energies produced by SNRs Observed range 1 1, 000, 000 GeV/n compared to E SNR max 10, 000 GeV/n Origins? Sources outside the Galaxy Quasars/Pulsars gamma ray bursts Exotic new physics: E.G. Dark Matter... Some cosmic rays are observed above expected rates... 7

8 PAMELA Payload for Antimatter Matter Exploration and Light nuclei Astrophysics 8

9 PAMELA Payload for Antimatter Matter Exploration and Light nuclei Astrophysics Satellite experiment launched in 2006 TOF (S1) geometric acceptance Primary goal: measure antimatter component of cosmic rays. Able to identify positively and negatively charged particles Measure spectra of antiprotons and positrons TOF (S2) spectrometer tracking system (6 planes) TOF (S3) calorimeter ~16.3 X0 ~0.6 l I magnet neutron detector B CARD CAT anticoincidence CAS Z Y X scint. S4 proton antiproton 9

10 PAMELA Results: Anti-Proton fraction PAMELA Collaboration (O. Adriani et al.), Phys.Rev.Lett.102:051101, IMAX 1992 BESS 2000 HEAT-pbar 2000 CAPRICE 1998 CAPRICE 1994 BESS-polar 2004 MASS 1991 BESS BESS 1999 PAMELA !10 Donato 2001 (D,!=500MV) Simon 1998 (LBM,!=500MV) Ptuskin 2006 (PD,!=550MV) PAMELA p/p p/p kinetic energy (GeV) kinetic energy (GeV) 2 10

11 PAMELA Results: Positron fraction PAMELA Collaboration (O. Adriani et al.), arxiv: [astro-ph] )) - )+!(e + ) / (!(e +!(e Positron fraction Muller & Tang 1987 MASS 1989 TS93 HEAT94+95 CAPRICE94 AMS98 HEAT00 Clem & Evenson 2007 )) - )+!(e + ) / (!(e +!(e Positron fraction PAMELA Energy (GeV) PAMELA Energy (GeV) 11

12 Balloon experiment collecting data in 2000, 2003 and 2007 ATIC Advanced Thin Ionization Calorimeter Cannot distinguish between and e + e Measures total electronic flux ( e + e + ) in energy range GeV Also detects protons and heavier nuclei Striking Results... 12

13 ATIC results ATIC Collaboration (J. Chang et al.), Nature 456: ,2008. AMS (green stars) HEAT (open black triangles) Emulsion chambers (black open diamonds) BETS (open blue circles) PPB-BETS (blue crosses) AMS and HEAT are satellite experiments BETS and PPB-BETS are balloon experiments Expected energy dependence of background Excess corresponds to 70 out of 210 total 13

14 Explaining the rise... Nearby astrophysical objects e.g. Pulsars See e.g. Büsching et al. Hooper et al. Profumo arxiv: arxiv: arxiv: Seems possible to explain PAMELA and ATIC with pulsars Dark Matter DM Decays τ s SM SM Many refs for dark matter, see e.g. Ref list in Profumo arxiv: DM DM Annihilations SM SM

15 Decaying dark matter Lifetime τ s Decays have restricted branching fractions: B HAD < 0.1 Candidates: Gravitino Hidden sector particle Composite particles Maybe others... Several ideas along these lines in literature

16 Annihilating dark matter 1) Annihilations rates must be large to account for large PAMELA and ATIC signals need boosts A problem for standard thermal dark matter 2) Annihilations must not produce too many hadrons Annihilation products usually include both hadrons and lepton 3) Annihilations must not produce too many photons Strong limits exist on photon signals Photons produced at wide range of frequencies for charged decay products

17 1) Annihilations rates must be largeproblem for standard thermal dark matter Particle in thermal eq. present abundance: n eq (m/t ) 3/2 e m/t However, if species freezes out i.e. Γ <H at temp T such that m/t 25 Kolb & Turner, `90 Can have significant relic abundance today Using Boltzmann equations we get Ω dm h 2 O( ) σv GeV 2 17

18 Ω dm h 2 O( ) σv GeV 2 But we know that Ω dm h 2 = ± σv = ( )GeV 2 This is weak scale interaction with weak scale mass particle This fixes σv WIMP sets the size of annihilations of DM particles as a function of DM velocity!! A way out!! Change how σv depends on velocity 18

19 The Sommerfeld Effect Normally σv = a + bv 2 Heavy DM moving at small (relative) velocity Exchange of scalar (or vector) state enhancement in annihilation cross section Corresponds to summation of diagrams DM σv 1 v r (Sommerfeld; Hisano et al, Strumia et al...) March-Russell, West, Cumberbatch, Hooper. Only significant for s-wave (AM barrier) DM 19

20 The Sommerfeld Effect Calculation formed in terms on non-rel two body QM problem with a potential Equivalent to distorted Born-wave approximation common in nuclear physics. Including the effect (to a good approximation) σ = Rσ l=0 tree Full calculation of R can be involved For a Yukawa potential R cannot be solved analytically Can be enhancement or suppression for vector exchange 20

21 Calculating R Introduce the following term λ 2 nψ dmψ dm Scalar n states can be the rungs on the ladder The Schrödinger equation for two DM particle state ψ ψ dm ψ dm 1 d 2 ψ m dm dr 2 + V ψ = Kψ V = λ2 K = m dm v 2 8πr e m n Enhancement factor R = ψ(0)/ψ( ) 2 Outgoing B.C ψ ( )/ψ( ) =im dm v 21

22 Coulomb limit Analytic form for R in limit ɛ m n /m dm =0 R = y 1 e y y = λ 2 /4v Small v limit R λ2 4v What about? ɛ 0 22

23 Enhancement for ɛ 0 ɛ m n /m dm Contours in R α = λ 2 /8π Need α/ɛ > α/β > 1 Log Α Ε 1.0 Freeze out β 0.2 λ 2 F O ID ID Log Α Β 23 F O Indirect detection β ID

24 3D Version March-Russell, West R Log[α/"] Log[α/β]

25 1) Annihilations rates must be large - Alternatives Could consider non-thermal dark matter Late decaying particles Another interesting idea later Over densities - No. annihilation ρ 2 dm Regions of high density Near Black Holes? Naturally occurring clumps?

26 2) Annihilations must not produce too many hadrons Leptophilic models Need to introduce extra quantum numbers dark matter only talks to leptons due to symmetries Kinematic tricks and extra symmetries DM DM φ Particle enhancement φ Fox, Poppitz, arxiv: µ, e µ, e (Arkani-Hamed et al...) can generate Sommerfeld Can introduce two dark matter states and have inelastic scattering possible to reconcile DAMA with other direct detection experiments

27 3) Annihilations must not produce too many photons All annihilations with charged states can produce photons Boosting annihilation rates into e ± means we produce more photons Measurements of Cosmic diffuse background radiation tightly constrain scenarios

28 Summry PAMELA and ATIC inspired a lot of model building Maybe explained by astrophysics If DM is the answer, need large boosts to annihilation cross sections Several ways to generate boost factors but all have restrictions and constraints PAMELA and ATIC data have inspired a lot of unusual and compelling new ideas - many more to come... Exciting times ahead