Dark matter Manoj Kaplinghat under our University of California, Irvine feet and in the sky Searching for Dark Matter Particles on Earth and in Space photo by Art Rosch Tuesday, June 26, 2012
• dark matter searches are well-motivated • the field is changing rapidly and experiments capable of “seeing” WIMP dark matter are finally operational • however , there are indications that we may have to extend the cold dark matter model • if so, then dark matter is not a WIMP Tuesday, June 26, 2012
what is the universe made of? • Normal matter (makes bacteria, comets, etc) • Dark matter (behaves gravitationally like normal matter but so far we no concrete evidence that it interacts with anything else) • More dark stuff (seriously!) dubbed dark energy (that does not behave gravitationally like normal matter) Background: The Hubble Ultra Deep Field Tuesday, June 26, 2012
is dark matter weird? • Doesn’t have to be. In fact, we would have been wondering why there isn’t any dark matter if all of Particles of matter was “normal”! the standard • Neutrinos are good dark model of matter candidates. Just particle not heavy enough to physics that make up all of the dark have been matter we see. seen in the laboratory Tuesday, June 26, 2012
what we see: some length scales pc (parsec) is Stellar nurseries 3 light-years or Galaxies 30 trillion km or Clusters of galaxies 200,000 AU 10 kpc 1 Mpc 10 pc Tuesday, June 26, 2012
what we see: some length scales Gigaparsecs Sloan Digital Sky Survey Filaments of structure -- the “cosmic web” Tuesday, June 26, 2012
dark matter in galaxies T y p i c a l s p e e d About half o f d m a r a k t t e r p gram of dark a r t i c l e a s b i o s u t 2 0 0 matter in a k m / t s h e n e s a o r l a cube with side r n e i g h b o r h o o d . 1000 km in the solar neighborhood Rotation speed Distance from center Tuesday, June 26, 2012
dark matter in galaxies Close-by and faint G C 4 3 9 5 U G C 7 5 2 4 / N Rotation supported by dark matter Tuesday, June 26, 2012
dark matter in galaxies: rotation speeds Note the plateau in speed as the distance from the center increases. This universal feature is the primary case for dark matter in galaxies. Note the linear rise in rotation speed close to the center. Tuesday, June 26, 2012
dark matter in clusters of galaxies: gravitational lensing Arcs are distorted images of background galaxies: “strong gravitational lensing” Tuesday, June 26, 2012
dark matter in clusters of galaxies: gravitational lensing Bullet cluster Blue: matter from “weak” gravitational lensing red: gas in x-rays Composite Credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Tuesday, June 26, 2012
dark matter on horizon scales WMAP (2003) COBE (1990) 2.7 degree Kelvin Bell labs (1964) The Universe is not perfectly smooth -- very small variations Discovered in are needed to make galaxies. 1990s with the WMAP : (a) universe is close to COBE satellite flat, and (b) about 5 times more dark matter than normal matter Tuesday, June 26, 2012
story so far We have looked at some of strongest lines of evidence for dark matter. The next section is about the basic questions we may ask about dark matter particles . Tuesday, June 26, 2012
Dark matter: Cold and Warm Cold/Warm: main Operational definitions distinction is (of course) temperature Cold dark matter: thermal motions irrelevant for Temperature: galaxy formation measure of random (thermal) motion Warm dark matter: thermal before dark matter motions (a) cut-off particles are bound formation of small-galaxies into halos (galaxies) or (b) reduce the amount of dark matter in the central As the universe cools, parts of galaxies this thermal motion decreases Tuesday, June 26, 2012
dark matter interactions (other than gravitation) Does it interact with other particles? Does it interact with itself? Is it stable? Tuesday, June 26, 2012
COLD dark matter on “large” scales Observations Matches data on cosmological scales (CMB) down to scales of order Mega-parsec (Galaxies) Zero-parameter fit (not counting the cosmological parameters) from Theory the astrophysical point of view Tuesday, June 26, 2012
extending cold dark matter model? Should we really expect dark sector to be so Cold dark matter model is simple (so much simpler clearly right (on large than the visible sector)? scales) but will it need modification as we probe smaller scales? If yes, what are the motivations? What sort of modifications? How may we test them? How does computing play into this? Tuesday, June 26, 2012
extending cold dark matter model (i) Warmer or (ii) Stronger self-interaction Actually... (i) much much ... warmer or (ii) much much ... stronger self-interaction How does warmness or strong self- interaction manifest itself in astrophysics? Next ... Tuesday, June 26, 2012
Milky Way halo simulated (almost...) Via Lactea: Diemand et al 2006 Milky Way stars Tuesday, June 26, 2012
Milky Way halo simulated (almost...) enclosed Mass Density Radius Radius (distance from center of (distance from center of clump or “subhalo”) clump or “subhalo”) Via Lactea Tuesday, June 26, 2012
Warmness and Self-interactions Self-interaction strength is dialed up Halo Density Distance from center of halo Warmer Number of halos of mass > M Mass M Tuesday, June 26, 2012
some models of Behaves like normal matter except it does not shine. dark matter Interacts very weakly with normal matter. SM AXION M A C H O LIGHT Particles from extra-dimensions WIMP ( W eakly I nteracting M assive P article) Self-interacting SuperWIMP Hidden sector Light Gravitino dark matter Self-annihilating warm Tuesday, June 26, 2012
Central density of halos is lowered WIMP Warmness Sterile ν SuperWIMP Hidden Damping Mass of smallest sector DM S e H l halos f a l i o n s t m e r o a a r n e c d t s i p o b h n i g e r g i e c r a l c o r e s Tuesday, June 26, 2012
Hidden Sector imagine proton if our sector is and neutron-like supersymmetric particles here SUSY Hidden SM Connector Tuesday, June 26, 2012
How is dark matter produced? Weak scale dark • By freeze-out process : stronger the matter self-annihilation smaller the present abundance (e.g., WIMP , x-dim) Right abundance! • Through decay process where the parent particle’s abundance is set via Successful the freeze-out mechanism (e.g., cosmological SuperWIMP) predictions on large scales • By non-thermal process (e.g., axions, sterile neutrino) Hints for new physics at the • Directly during reheating : fine weak scale (~1000 tuned (e.g., WIMPZILLA) proton masses) Tuesday, June 26, 2012
story so far • We have seen that well-motivated dark matter models are varied and they make differing predictions for: • formation of small galaxies • for density of dark matter in the central parts of the galaxy • WIMPs are the favored candidates • well-motivated • provide the most dramatic avenues for seeing dark matter -- Direct detection, Indirect detection, Direct production. Coming up next ... Tuesday, June 26, 2012
dark matter is all around us: how do we “see it”? Tuesday, June 26, 2012
the WIMP casebook • Weakly Interacting Massive Particle • Weakly interacting: this is what makes dark matter effectively “dark”. The weak interactions also endow the dark matter with the right cosmological abundance. • “Massive”: has to be or we would have seen it in the lab despite the weak interactions • These particles fall out of theories designed to complete the standard model of particle physics Tuesday, June 26, 2012
Indirect detection q, e protons, DM anti-protons, electrons, Fermi (gamma-rays) anti-electrons, photons anti-q, DM anti-e Stay tuned for results from AMS-02 PAMELA (antimatter) Tuesday, June 26, 2012
Sources for indirect detection Satellites of the Milky Way Not all these Milky Way clumps light up Both the center of the Milky Way and satellites of the stars (form stars)! Milky Way have large concentrations of dark matter. But some have So look towards them for indirect signatures of dark to and we can matter (other than gravitational). look towards them. Tuesday, June 26, 2012
Direct detection recoils with energy DM DM of order (DMP DAMA mass)(200 km/s) 2 COGENT CRESST number of events proton proton depends on: (a) how strongly DMP Cryogenic couples to protons Dark Xenon Gran Sasso and neutrons, and Matter (b) how many DMPs Dark Search per meter 3 in the Matter (Soudan) solar neighborhood Search Tuesday, June 26, 2012
Direct production Make dark matter! Large Hadron Collider DM anti- quarks DM quarks Tuesday, June 26, 2012
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