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Particle Dark Matter an Introduction Into Evidence, Models, and Direct Searches

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Particle Dark Matter an Introduction Into Evidence, Models, and Direct Searches Particle Dark Matter An Introduction into Evidence, Models, and Direct Searches Lecture for ESIPAP 2016 European School of Instrumentation in Particle & Astroparticle Physics Archamps Technopole XENON1T January 25th, 2016 Uwe Oberlack Institute of Physics & PRISMA Cluster of Excellence Johannes Gutenberg University Mainz http://xenon.physik.uni-mainz.de Outline ● Evidence for Dark Matter: ▸ The Problem of Missing Mass ▸ In galaxies ▸ In galaxy clusters ▸ In the universe as a whole ● DM Candidates: ▸ The DM particle zoo ▸ WIMPs ● DM Direct Searches: ▸ Detection principle, physics inputs ▸ Example experiments & results ▸ Outlook Uwe Oberlack ESIPAP 2016 2 Types of Evidences for Dark Matter ● Kinematic studies use luminous astrophysical objects to probe the gravitational potential of a massive environment, e.g.: ▸ Stars or gas clouds probing the gravitational potential of galaxies ▸ Galaxies or intergalactic gas probing the gravitational potential of galaxy clusters ● Gravitational lensing is an independent way to measure the total mass (profle) of a foreground object using the light of background sources (galaxies, active galactic nuclei). ● Comparison of mass profles with observed luminosity profles lead to a problem of missing mass, usually interpreted as evidence for Dark Matter. ● Measuring the geometry (curvature) of the universe, indicates a ”fat” universe with close to critical density. Comparison with luminous mass: → a major accounting problem! Including observations of the expansion history lead to the Standard Model of Cosmology: accounting defcit solved by ~68% Dark Energy, ~27% Dark Matter and <5% “regular” (baryonic) matter. ● Other lines of evidence probe properties of matter under the infuence of gravity: ▸ the equation of state of oscillating matter as observed through fuctuations of the Cosmic Microwave Background (acoustic peaks). ▸ formation of structure in the universe, probing the velocity dispersion of (dark) matter. Uwe Oberlack ESIPAP 2016 3 The Problem of Missing Mass Uwe Oberlack ESIPAP 2016 4 Evidence for Dark Matter In Galaxies Scale: 1021 m (~10 5 lightyears) Spiral galaxies Dwarf Spheroidal galaxies M31, NASA Fornax David Malin, Anglo-Australian Observatory. Uwe Oberlack ESIPAP 2016 5 Our Galaxy The Milky Way Our view from inside the disk (in near infrared radiation) 2MASS Allsky survey Edge-on view (sketch) Uwe Oberlack ESIPAP 2016 6 Stellar Orbits Pearson Education Uwe Oberlack ESIPAP 2016 7 Evidence for Dark Matter in Spiral Galaxies Rotation curves (orbital velocity vs. galactocentric radius) remain fat well beyond the edge of the visible disk in spiral galaxies. Disk + DM Halo Disk only Rotation curves of nearby galaxies Rotation curve of the Milky Way (Sofue & Rubin ARAA 2001) (A. Klypin et. al, ApJ. 573, 2002) Uwe Oberlack ESIPAP 2016 8 Via Lactea 2 (2008) http://www.ucolick.org/~diemand/vl Dark Matter Halo Observer Uwe Oberlack ESIPAP 2016 9 MOND: Modifed Newtonian Dynamics Mordehai Milgrom 1983 Change Newton´s force law for low values of acceleration a: For large r, a << a0: For a circular orbit: so is independent of r. If, a >> a0: 1, so v remains ● MOND does well for rotation curves but does not explain the movement of galaxies in clusters or cosmological observations. ● MOND is a non-relativistic theory, phenomenological, and ad hoc. More sophisticated relativistic theory (e.g., TeVeS) also has difculty explaining cosmological data. Uwe Oberlack ESIPAP 2016 10 Local DM density from vertical motions Uwe Oberlack ESIPAP 2016 11 Evidence for Dark Matter in Galaxy Clusters • Orbital velocities of galaxies exceed escape velocity estimated from visible mass in galaxies (Zwicky 1933). • X-ray gas: pressure too great for visible mass. Traces gravitational potential. NOAO/Kitt Peak: Uson, Dale • Gravitational lensing: measures total NASA/CXC/IoA: Allen et al. mass distribution in galaxy clusters. Scale: ~1022 m (~106 lightyears) W. Couch, R. Ellis, NASA G. Kochanski, I. Dell'Antonio, T. Tyson, 2002 Uwe Oberlack ESIPAP 2016 12 Velocity dispersion in galaxy clusters Fritz Zwicky (1933) used the velocity dispersion of galaxies in the Coma cluster and the virial theorem 1 E = − E kin 2 pot to estimate the mass of the cluster MCluster. Comparing this mass to the luminosity of the galaxies in the cluster, using empirical relations between luminosity and mass for stars, he found: Mlum ~ 1/400 MCluster Something is missing : Dark Matter ? Helvetica Physica Acta 6 (1933), 110 Uwe Oberlack ESIPAP 2016 13 X-Ray Observations of Galaxy Clusters Baryonic matter in galaxy clusters is dominated by X-ray emitting hot gas. The temperature of the hot gas tells us the total cluster mass. 85% dark matter 13% hot gas Zwicky knew 2% stars only about this! This results from the assumption that the observed clusters are virialized, i.e., Epot = 2 Ekin Kinetic energy=thermal energy 1 2 3 m ⟨ v ⟩= k T 2 ¯ 2 virial with avg. particle mass m¯ ≈1.23mH Boltzmann constant: k=1.38065×10−23 J / K ⇒ Velocity dispersion: σ=√ ⟨ v2 ⟩ 3 k T 3 1 T σ= ≈1.4×10 km s− √ m¯ √ 108 K 3 −1 7 Uwe Oberlack ESIPAP 2016 σ∼10 km s ,T ∼(2−11)×1014 K Gravitational Lensing General Relativity: A massive object (e.g., a galaxy cluster) curves spacetime. Light follows geodesics. Hence a massive object acts as a gravitational lens for light from a distant source. Gravitational lensing measures the total mass enclosed by the light rays, independent of the type of matter. NASA/ESA Uwe Oberlack ESIPAP 2016 15 Gravitational Lensing: Strong Lensing NASA/ESA Gravitational lensing measures the total mass enclosed by the light rays, independent of the type of matter. Uwe Oberlack ESIPAP 2016 16 Weak Lensing ● Line of sight near galaxy cluster: strong lensing (long arcs) ● Further out: weaker distortions, but more abundant. → weak lensing ● Measure total mass distribution in galaxy clusters NASA HST Bullet cluster blue: total mass distribution from weak lensing NASA Uwe Oberlack ESIPAP 2016 17 MergingMerging GalaxyGalaxy Clusters:Clusters: MissingMissing massmass oror modificationmodification ofof gravity?gravity? D. Clowe et al., 2006 Bullet Cluster 18 Uwe Oberlack ESIPAP 2016 The Bullet Cluster ● “Bullet cluster” (z~0.3) is an ongoing merger of two galaxy clusters. ● Cores passed through each other ~100 million years ago (recent!). ● Weak lensing observations (blue) trace the total mass distribution. ● Known property of clusters: bulk of regular (baryonic) matter consists of hot intra- cluster gas. Stars contribute just a little. ● Chandra X-ray observations (pink) trace hot intracluster gas, i.e., most baryons. D. Clowe et al., Astrophys. J. 648 (2006) L109 ● Stars and Dark Matter are collisionless, whereas gas (plasma) experiences ram pressure. ● Mass cluster >> Mass gas ● Bulk of total mass ofset with respect to ● Gas is ofset with respect to total matter bulk of baryonic matter. distribution. ⇒Dark Matter! But: these systems are rare, dynamics ... and not modifed gravity. complicated, possible counter example, etc. Uwe Oberlack ESIPAP 2016 19 Scale: ~1026 m Planck Collab. arxiv:1303.5062 Evidence for Dark Matter (1010 lightyears) CMB Ω ≈ 5 Ω from Cosmology m b ● Cosmic Microwave Background. ▸ Uniformity at age 380,000 yr. ▸ Flatness of the universe ▸ Baryon density, etc. ● Supernovae as standard candles. ▸ Expansion history of the universe. ● Galaxy surveys (wide or deep) and Simulations of structure formation. ▸ Large scale structure. ▸ Early structure formation. First stars. Quasars and galaxies. ● Big Bang Nucleosynthesis and light element Dark Energy abundances observed in the early universe. Dark Matter ▸ Limit on baryon density, consistent Baryons with CMB. 68.3% ● Baryon Acoustic Oscillations 26.8% ▸ standard ruler ● ... 4.9% Uwe Oberlack ESIPAP 2016 20 Multipole Expansion of CMB WMAP after dipole subtraction Expansion in spherical l=2 harmonics: Pair correlation function: l=3 2 C (Δ T ) = l (l + 1) l Uwe Oberlack 2 π ESIPAP 2016 NASA/WMAP 21 CMB Power Spectrum & Baryon Density P. Schneider Relative strength of acoustic peaks provides Ωm and Ωb independently. Uwe Oberlack ESIPAP 2016 22 CMB as seen by Planck: Power Spectra Planck collaboration, arxiv:1303.5062 Uwe Oberlack ESIPAP 2016 23 → Dark Matter is non-baryonic. Uwe Oberlack ESIPAP 2016 24 Structures in galaxy maps look very similar to the ones found in models in which dark matter is “cold” (v ≪ c) and not interacting, supporting WIMPs as Dark Matter candidates. Uwe Oberlack ESIPAP 2016 25 Cold Dark Matter – Structure Formation V. Springel, C. S. Frenk, S. D. M. White Nature 440, 1137 (2006) Uwe Oberlack ESIPAP 2016 26 → Dark Matter is non-relativistic: cold, or at least not hot. Uwe Oberlack ESIPAP 2016 27 Non-baryonic Dark Matter or Alternative Theories of Gravity? CMB Ωm≈ 5 Ωb Planck 3rd peak only with Dark Matter ● Relative strength of acoustic peaks provides Ωm and Ωb independently. ● One can also test for alternative theories of gravitation (e.g., TeVeS): no alternative theory can do without Dark Matter. Uwe Oberlack ESIPAP 2016 28 Non-baryonic Dark Matter or Alternative Theories of Gravity? Matter power spectra SDSS TeVeS M D ΛC Dodelson, arXiv:1112.1320 Uwe Oberlack ESIPAP 2016 29 Outline ● Evidence for Dark Matter: ▸ The Problem of Missing Mass ▸ In galaxies ▸ In galaxy clusters ▸ In the universe as a whole ● DM Candidates: ▸ The DM particle zoo ▸ WIMPs ● DM Direct Searches: ▸ Detection principle, physics inputs ▸ Example experiments & results ▸ Outlook Uwe Oberlack ESIPAP 2016 30 What do we know about Dark Matter? ● Gravitationally interacting The Standard Model ► How we know
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