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DARK MATTER IN THE MILKY WAY

DARK MATTER IN THE MILKY WAY. ALEXEY GLADYSHEV (JINR, DUBNA & ITEP, MOSCOW) SMALL TRIANGLE MEETING 2005. Outlook. Introduction. Evidence for Dark Matter. Types of Dark Matter. Direct searches for the Dark Matter. EGRET data: an excess of the diffuse gamma ray flux

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DARK MATTER IN THE MILKY WAY

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  1. DARK MATTER IN THE MILKY WAY ALEXEY GLADYSHEV (JINR, DUBNA & ITEP, MOSCOW) SMALL TRIANGLE MEETING 2005

  2. Outlook • Introduction. • Evidence for Dark Matter. Types of Dark Matter. Direct searches for the Dark Matter. • EGRET data: an excess of the diffuse gamma ray flux • Dark matter distribution in the Milky Way. Halo density profile. Halo substructure. The Milky Way rotation curve. • Positrons and antiprotons in the cosmic rays • WMAP and EGRET constraints in Constrained Minimal Supersymmetric Standard Model • Conclusions A Gladyshev (JINR & ITEP) Small Triangle 2005

  3. Basic cosmological parameters • Density parameters – ratios of contributions of different components (matter, radiation, etc.) to the critical density • Consider the Friedmann equation in the most general form (including the cosmological constant) A Gladyshev (JINR & ITEP) Small Triangle 2005

  4. Basic cosmological parameters • Then we can define density parameters corresponding to the matter, radiation, cosmological constant, and even spatial curvature • The Friedmann equation can be rewritten then in the form A Gladyshev (JINR & ITEP) Small Triangle 2005

  5. Basic cosmological parameters • For today (a= a0 , H= H0) it corresponds to the cosmic sum rule In the context of the Friedmann-Robetrson-Walker metric the total fraction of radiation, matter, curvature and cosmological constant densities must add up to unity A Gladyshev (JINR & ITEP) Small Triangle 2005

  6. Basic cosmological parameters • In the year 2000, two CMBR missions, BOOMERANG and MAXIMA confirmed that the Universe’s geometry should be very close to flat. • The BOOMERANG result in 2001 gave • The WMAP data released in February 2003 were consistent with A Gladyshev (JINR & ITEP) Small Triangle 2005

  7. Basic cosmological parameters • The radiation component R, corresponding to relativistic particles from the density of the cosmic microwave background radiation is which gives R= 2.4  10-5 h-2 = 4.8  10-5. Three massless neutrinos contribute an even smaller amount. Therefore one can safely neglect the contribution of relativistic particles to the total density of the Universe A Gladyshev (JINR & ITEP) Small Triangle 2005

  8. Matter in the Universe • The matter contribution to the total density of the Universe can be independently estimated in different ways • Estimation from the dynamics of clusters. A cluster mass Mcl can be defined by consideration of galaxy motion within the cluster and/or by gravitational lensing by a cluster gravitational potential. An estimate of the mass of matter in the Universe would be then L are luminosities of a cluster and of the Universe as a whole. A Gladyshev (JINR & ITEP) Small Triangle 2005

  9. Matter in the Universe • This gives the estimate • Another estimate comes from the baryon fraction in matter • Yet another estimate comes from consideration of cluster abundances A Gladyshev (JINR & ITEP) Small Triangle 2005

  10. WMAP • WMAP mission has provided the first detailed full-sky map of the microwave background radiation in the Universe A Gladyshev (JINR & ITEP) Small Triangle 2005

  11. A Gladyshev (JINR & ITEP) Small Triangle 2005

  12. WMAP • Results of WMAP Combination with other cosmic experiments gives A Gladyshev (JINR & ITEP) Small Triangle 2005

  13. Evidence for the Dark Matter • First evidence for the dark matter – motion of galaxies within clusters (F.Zwicky, 1933) • The most direct evidence for the existence of large amount of the dark matter are the flat rotation curves of spiral galaxies (the dependence of the linear velocity of stars on the distance to the galactic center) • Spiral galaxies consist of a rather thin disc and a spherical bulb in the galactic center A Gladyshev (JINR & ITEP) Small Triangle 2005

  14. Evidence for the Dark Matter • From the equality of forces one gets • Assuming spherical distribution of mass in the core one gets inner part outer part Solar system rotation curve A Gladyshev (JINR & ITEP) Small Triangle 2005

  15. Evidence for the Dark Matter • Observation tell us that for large radii r which means linear distribution of mass This points to the existence of the huge amount of dark matter surrounding the visible part of the galaxy Contribution of the dark matter halo alone Contribution of the disc (visible stars) alone A Gladyshev (JINR & ITEP) Small Triangle 2005

  16. Evidence for the Dark Matter • Nowadays, thousands of galactic rotation curves are known, and they all suggest the existence of about ten times more mass in the halos than in the stars of the disc Elliptic galaxies and cluster of galaxies also contain a large amount of the dark matter A Gladyshev (JINR & ITEP) Small Triangle 2005

  17. Evidence for the Dark Matter • The Milky Way rotation curve has been measured and confirms the usual picture • Measurements of velocities of Magellanic Clouds tells that the Milky Way has very large and massive halo • VIRGOHI21 object – a galaxy, consisting only of dark matter A Gladyshev (JINR & ITEP) Small Triangle 2005

  18. Matter content of the Universe • The matter content of the Universe is determined by the mass density parameter M. the possible contributions are The luminous baryonic matter (stars in galaxies) The hot dark matter (massive neutrinos ? ) The dark baryonic matter (MAssive Compact Halo Objects - MACHOs ? ) The cold dark matter (Weakly Interacting Massive Particles - WIMPs - neutralinos ? ) A Gladyshev (JINR & ITEP) Small Triangle 2005

  19. Matter content of the Universe • All the luminous matter in the Universe from galaxies, clusters of galaxies, etc. is and is very far from the critical density • Deuterium from the primordial nucleosynthesis provides a good test for the matter density (Large density - Fast interactions - Lower abundance) Observation of primordial deuterium abundance gives • Thus, besides luminous matter there exist invisible baryonic matter, with a mass more than ten times larger. A Gladyshev (JINR & ITEP) Small Triangle 2005

  20. Dark Matter candidates • Baryonic Dark Matter(MACHOs – MAssive Compact Halo Objects) • Normal stars No, since they would be luminous • Hot gas No, since it would shine • Burnt-out stellar remnants seems implausible, since they would arise from a population of normal stars of which there is no trace in the halo • Neutron stars No, since they would arise from supernova explosions and thus eject heavy elements into the galaxy A Gladyshev (JINR & ITEP) Small Triangle 2005

  21. Dark Matter candidates • Baryonic Dark Matter(MACHOs – MAssive Compact Halo Objects) • White dwarfs (stars with a mass which is not enough to reach the supernova phase): possible, since white dwarfs are known to exist and to be plentiful. Maybe they could be plentiful enough to explain the Dark Matter if young galaxiesthatproduced white dwarfs cool more rapidly than present theory predicts.But the production of large numbers of white dwarfs implies the production of a large amount of helium, which is not observed A Gladyshev (JINR & ITEP) Small Triangle 2005

  22. Dark Matter candidates • Baryonic Dark Matter(MACHOs – MAssive Compact Halo Objects) • Brown dwarfs (stars ten times lighter than the Sun)possible Astronomers have found some objectsthat are either brown dwarf stars or very large planets. However,there is no evidence that brown dwarfs are anywhere near as abundant as they would have to be to account for the Dark Matter in our galaxy A Gladyshev (JINR & ITEP) Small Triangle 2005

  23. Dark Matter candidates • Non-baryonic “hot” dark matter • Massive neutrinos Today we have a convincing evidence of neutrino oscillations.This means that neutrinos have a mass. The measurable quantity – mass-squared difference. If neutrino mass is as large as , their contribution to the total density of the Universe is comparable to the contribution of the luminous baryonic matter! A Gladyshev (JINR & ITEP) Small Triangle 2005

  24. Dark Matter candidates • Non-baryonic “cold” dark matter The most reasonable explanation – weakly interacting massive particles(WIMP’s) WIMP’s could have been produced in the Big Bang origin of the Universe in the right amounts and with the right properties to explain the Dark Matter BUT: we do not know WHAT the WIMP IS A Gladyshev (JINR & ITEP) Small Triangle 2005

  25. Direct searches for the Dark Matter • Optical observations from the Earth (EROS, MACHO, … ) • Underground searches (DAMA, EDELWEISS, CDMS, … ) • Underwater searches (ANTARES, … ) • Searches in space (AMS, … ) A Gladyshev (JINR & ITEP) Small Triangle 2005

  26. Direct searches for the Dark Matter • MACHO experiment(MAssive Compact Halo Object) • Location - Mount Stromlo Observatory, Canberra, Australia • Main goal - search for objects like brown dwarfs or planets (Massive Compact Halo Objects - MACHOs) • Signature - occasional amplification of the light by the gravitational lens effect A Gladyshev (JINR & ITEP) Small Triangle 2005

  27. Direct searches for the Dark Matter • The effect is large and easily detectable: the amplification could be as large as 0.75m • The phenomenon has a very symmetric light curve, characterized by only 3 parameters (brightness in the maximum, time and duration of the light amplification) • The amplification is the same for all wavelenghts • For the particular star the effect can take place only once A Gladyshev (JINR & ITEP) Small Triangle 2005

  28. Direct searches for the Dark Matter • Different collaborations have seen the signal (1993-1996) OGLE 18 candidates in the direction to the galactic centre MACHO 120 DUO 10 Gravitional lens effect has been detected also in the direction to the Large Magellanic Cloud MACHO 8 EROS 2 The most probable mass of the lens However, MACHOs can only account for less than ~ 50 % of the halo A Gladyshev (JINR & ITEP) Small Triangle 2005

  29. Direct searches for the Dark Matter • DAMA experiment (DArk MAtter) • Location - Gran Sasso National Laboratoryof I.N.F.N. • Main goal - search for dark matter particles: WIMPs • Main process – WIMP elastic scattering on the target nuclei • Measured quantity - nuclear recoil energy in the keV range A Gladyshev (JINR & ITEP) Small Triangle 2005

  30. Direct searches for the Dark Matter • Positive evidence for a WIMP signal could arise from the kinematics of the Earth withing non-rotating WIMP halo. The sun is orbiting about the galactic centre with a velocity of ~ 220 km/s. The Earth is orbiting about the Sun with a velocity of ~ 30 km/s. • The resulting relative Earth-halo velocity is modulated, thus the WIMP flux is also modulated which should lead to the modulation of the count rate. A Gladyshev (JINR & ITEP) Small Triangle 2005

  31. Direct searches for the Dark Matter • DAMA group claim they do observe the modulation of their count rate (results of 4 years running - 57986 kgd) A Gladyshev (JINR & ITEP) Small Triangle 2005

  32. Direct searches for the Dark Matter • This result is compatible with a signal from WIMPs with a mass and a WIMP-nucleon cross section of A Gladyshev (JINR & ITEP) Small Triangle 2005

  33. Direct searches for the Dark Matter • Severe criticism has arisen in the community, ascribing the observed annual modulation rater to systematics than to a WIMP signature. DAMA insists on their model-independent analysis: • presence of annual modulation with the proper features; • neither systematics nor side reactions able to mimic the signature A Gladyshev (JINR & ITEP) Small Triangle 2005

  34. Direct searches for the Dark Matter • 1st data taking: Fall 2000 2nd data taking: 1st semester 2002 3rd data taking :October 2002 - March 2003 • EDELWEISS new limits • DAMA best fit exclusion at > 99.8 % C.L confirmed with 3 new detectors and extended exposure • Exclusion limits are astrophysical model independent A Gladyshev (JINR & ITEP) Small Triangle 2005

  35. Direct searches for the Dark Matter • EDELWEISS II • New run started : improved energy threshold • Expect further factor > 2 in exposure with improved sensitivity • September 2003 : EDELWEISS I stops and EDELWEISS II installation begins with 21×320g Ge • Sensitivity will be improved by a factor of 100 A Gladyshev (JINR & ITEP) Small Triangle 2005

  36. Searches for the Dark Matter • AMS-02experiment(AntiMatter in Space) • Location - International Space Station (Hopes it’ll be launched in 2007, scheduled to be launched 15 Oct 2005, planned 4 Sep 2003) • Main Goal - search for dark matter, missing matter & antimatterin space A Gladyshev (JINR & ITEP) Small Triangle 2005

  37. Indirect searches for the Dark Matter

  38. EGRET Excess • EGRET Data on diffuse Gamma Rays show excess in all sky directions with the same energy spectrum from monoenergetic quarks • 9 yrs of data taken (1991-2000) • Main purpose: sky map of point sources above diffuse background. A Gladyshev (JINR & ITEP) Small Triangle 2005

  39. EGRET Excess A: Inner Galaxy (l=±300, |b|<50) B: Galactic plane avoiding A (30-3300) C: Outer Galaxy (90-2700) D: Low latitude (10-200) E: Intermediate lat. (20-600) F: Galactic poles (60-900) Excess has the same shape implying the same source everywhere in the galaxy A Gladyshev (JINR & ITEP) Small Triangle 2005

  40. EGRET Excess A: Inner Galaxy (l=±300, |b|<50) B: Galactic plane avoiding A (30-3300) C: Outer Galaxy (90-2700) D: Low latitude (10-200) E: Intermediate lat. (20-600) F: Galactic poles (60-900) Excess has the same shape implying the same source everywhere in the galaxy EGRET gamma excess above extrapolated background from data below 0.5 GeV A Gladyshev (JINR & ITEP) Small Triangle 2005

  41. EGRET Excess A: Inner Galaxy (l=±300, |b|<50) B: Galactic plane avoiding A C: Outer Galaxy D: Low latitude (10-200) E: Intermediate lat. (20-600) F: Galactic poles (60-900) A Gladyshev (JINR & ITEP) Small Triangle 2005

  42. EGRET Excess vs WIMP annihilation • The excess of diffuse gamma rays is compatible with WIMP mass of 50 -100 GeV • Region A: inner Galaxy (l=±300, |b|<50) Background WIMP contribution A Gladyshev (JINR & ITEP) Small Triangle 2005

  43. EGRET Excess vs WIMP annihilation A: inner Galaxy (l=±300, |b|<50) B: Galactic plane avoiding A C: Outer Galaxy D: low latitude (10-200) E: intermediate lat. (20-600) F: Galactic poles (60-900) A Gladyshev (JINR & ITEP) Small Triangle 2005

  44. WIMP mass 50 - 100 GeV EGRET Excess vs WIMP annihilation • 3 components (galactic background + extragalactic background + DM annihilation) fitted simultaneously with same WIMP mass and DM normalization in all directions. • Blue:uncertainty from WIMP mass 65 100 0 WIMPS A Gladyshev (JINR & ITEP) Small Triangle 2005

  45. Determination of halo profile • The differential gamma flux in a direction forming an angle ψ with the direction of the galactic center is given by: differential photon yield for the final state f Dark matter mass density WIMP annihilation cross section branching ratio into the tree-level annihilation final state f Boostfactor WIMP mass A Gladyshev (JINR & ITEP) Small Triangle 2005

  46. Determination of halo profile • A survey of the optical rotation curves of 400 galaxies shows that the halo distributions of most of them can be fitted either with the Navarro-Frank-White (NFW) or the pseudo-isothermal profile. The halo profiles can be parametrized as follows: ais a scale radius, define behaviour at r ≈ a, r >> a and r << a A Gladyshev (JINR & ITEP) Small Triangle 2005

  47. Determination of halo profile • Navarro-Frank-White profile (1,3,1) very cuspy • Moore profile (1.5,0,1.5) very cuspy • Isotermal profile (2,2,0) less cuspy β=2 implies flat rotation curve A Gladyshev (JINR & ITEP) Small Triangle 2005

  48. Determination of halo profile • The spherical profile can be flattened in two directions to form a triaxial halo. N-body simulations suggest the ratio of the short (intermediate) axis to the major axis is typically above 0.5-0.7 • It is not clear if the dark matter is homogeneously distributed or has a clumpy character. Clumps can enhance the annihilation rate. This enhancement (boostfactor) can be determined from a fit to the data. A Gladyshev (JINR & ITEP) Small Triangle 2005

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