components Particle Astrophysics, chapter 7

Transcription

1 Dark matter and dark energy components Particle Astrophysics, chapter 7

2 Overview lecture 3 Observation of dark matter as gravitational ti effects Rotation curves galaxies, mass/light ratios in galaxies Velocities of galaxies in clusters Gavitational lenses Matter-energy energy density in the universe Primordial nucleosynthesis CMB measurements with WMAP Nature of dark matter particles - models: Baryons and MACHO s Neutrinos Axions Weakly Interacting Massive Particles (WIMPs) Experimental WIMP searches: direct and indirect detection chapter 7 astro-particle physics

3 Evidence for dark matter -1 Observations at different scales : more matter in the universe than what is measured as electromagnetic radiation (visible light, radio, IR, X-rays rays, g-rays) Visible matter = stars, interstellar gas, dust : light & atomic spectra (mainly H) Velocities of galaxies in clusters Æ high mass/light ratios M MMW Mcluster = L L L Rotation curves of stars in galaxies Æ large missing mass up to MW large distance from centre cluster chapter 7 astro-particle physics

4 Evidence for dark matter -2 Gavitational lensing by galaxy clusters Æ effect larger than expected from visible matter chapter 7 astro-particle physics

5 Baryon content of universe Baryon content of universe from measurement of light element abundances and Big Bang Nucleosynthesis model N B N γ 10 ( ) 10 η = = ± Ω = ± B chapter 7 astro-particle physics

6 Dark matter mapping chapter 7 astro-particle physics

7 MACHOs = Massive Compact Halo Objects Baryons Neutrinos Axions WIMPs = Weakly Interacting Massive Particles NATURE OF DARK MATTER chapter 7 astro-particle physics

8 What are we looking for? Particles with mass interact gravitationally Particles which are not observed in radio, IR, visible, X-rays, g- rays : neutral and weakly interacting Candidates: Dark baryonic matter: baryons, MACHOs light particles in large quantities: primordial neutrinos, axions Heavy particles in small quantities: need new type of particles like neutralinos, Kaluza-Klein particles, (WIMPs) Formation of structures: majority of dark matter particles were non relativistic at time of freeze-out fi Cold Dark Matter chapter 7 astro-particle physics

9 BARYONIC DARK MATTER chapter 7 astro-particle physics

10 Baryon budget of universe From BB nucleosynthesis and CMB fluctuations: Related to history of universe at z=10 9 and z=1000 Most of baryonic matter is in stars, gas, dust Small contribution of luminous matter fi 80% of baryonic mass is dark Ωbaryons Ωlum Inter Gallactic Matter = gas of hydrogen in clusters of galaxies Absorption of Lya emission from distant quasars yields neutral hydrogen fraction in inter gallactic regions Most hydrogen is ionised and invisible in absorption spectra fi form dark baryonic matter chapter 7 astro-particle physics

11 Lya forest and hydrogen gas Hydrogen atoms Absorb UV light Measurement of absorption spectra yields amount of neutral H Emission of UV light by quasar l= 1216 Ǻ Lyman a transition in H chapter 7 astro-particle physics

12 Lya forest Hydrogen spectrum from distant quasar absorption at different redshift values due to atomic hydrogen chapter 7 astro-particle physics

13 Baryon budget of universe Negligible contribution from micro black holes BHs must have M BH < 10 5 M Ω < 10 Heavier BH would yield lensing effects which are not observed BH 7 small contribution of MACHOS = dark stars observed in Milky Way through gravitational microlensing chapter 7 astro-particle physics

14 Massive Astrophysical Compact Halo Objects Dark stars in the halo of the Milky Way Observed through microlensing of large number of stars MACHOS chapter 7 astro-particle physics

15 Microlensing Light of source is amplified by gravitational lens When lens is small (star, planet) multiple images of source cannot be distinguished : addition of images = amplification But : amplification effect varies with time as lens passes in front of source - period T Efficient for observation of e.g. faint stars Period T chapter 7 astro-particle physics

16 Microlensing - MACHOs Amplification of signal by addition of multiple images of source Amplification varies with time of passage of lens in front of source 2 2 x x t A= 1 + / x 1+ x 2 4 T Typical time T : days to months depends on distance & velocity MACHO = dark astronomical object seen in microlensing M ª M A few have been observed in halo of Milky Way Account for very small fraction of dark baryonic matter MACHO project launched in 1991: monitoring during 8 years of microlensing in direction of Large Magellanic Cloud chapter 7 astro-particle physics

17 Optical depth Optical depth t = probability bilit thatt source undergoes gravitational ti lensing N L = density of lenses in line of sight to source, uniformly distributed D S 2 2 q E = Einstein radius of lensing τ = π D θ N dd For r = N L M = Mass density of lenses 0 Optical depth depends on distance of source number of lenses Near periphery of bulge of Milky Way fi record microlensing for millions of stars τ L E L L D S τ = 2πG c 2 ρ 3 7 ( per source) 10 Experiments: MACHO, EROS, supermacho, EROS-2 EROS-2: 33x10 6 stars monitored, one candidate MACHO found fi less than 8% of halo mass are MACHOs chapter 7 astro-particle physics

18 Example of microlensing source = star in Large Magellanic Cloud (LMC, distance = 50kpc) Dark matter lens in form of MACHO between LMC star and Earth Effect π variable star because same observation of luminosity in red and blue light : expect that gravitational deflection is independent of wavelength chapter 7 astro-particle physics

19 NEUTRINOS AS DARK MATTER chapter 7 astro-particle physics

20 Relic neutrinos Non-baryonic dark matter = particles created during hot phase of early universe Stable and surviving till today Neutrino from Standard Model = possible candidate from particle physics: Neutrino production and annihilation in early universe weak kinteractionsi γ e + + e ν + ν i = e, μ, τ Neutrinos freeze-out during radiation dominated d era when kt ª 3MeV and t ª 0.3s 3 3 Relic neutrino density N ν ( 0 ) = ( 0 ) = 1 13 i Nγ cm 11 and temperature today Tν ( 0 ) = Tγ ( 0 ) = K mev 11 chapter 7 astro-particle physics i i

21 Neutrinos as dark matter 3 Total density for all flavours Nν 340 cm High density, of order of CMB but difficult to detect! Upper limit on neutrino mass from cosmology: If all critical density today = 3 flavours of neutrinos e, μτ, mc = 47 ev m < 16eV c ν 2 2 ν From neutrino oscillations: masses of order 0.1eV/c2 fi low contribution of neutrino DM Relic neutrinos can only be Hot Dark Matter HDM Were relativistic when decoupling from other matter ktª3mev Relativistic particles prevent formation of large-scale structures From simulations of structures: maximum 30% of DM is hot chapter 7 astro-particle physics

22 simulations Hot dark matter warm dark matter cold dark matter Observations 2dF galaxy survey chapter 7 astro-particle physics

23 AXIONS chapter 7 astro-particle physics

24 Strong CP problem CPT = symmetry of all interactions ti CP symmetry is partly violated in weak interactions introduced in Standard Model by complex phase between quarks (CKM matrix) CP violation is present through a parameter of QCD (theory for strong interactions) but is not observed why not? would yield non-zero neutron electric dipole moment much larger than experimentally upper limit pred e d 10 ecm. de < 10 ecm. Solution by Pecci-Quinn : introduce higher global symmetry, exp which is broken at energy scale f a Associated boson = axion with mass Is light and weakly interacting m a = 6eV 6 10 GV GeV f a chapter 7 astro-particle physics

25 Axion as dark matter Weak couplings to SM particles Decoupled in early universe if mass ª ev its lifetime is larger than the lifetime of universe Æ stable Production in photon plasma in Sun or SuperNovae Searches via decay to 2 photons in magnetic field + a + production decay γ γ γ γ CAST CERN: axions from Sun Candidate for cold dark matter If axion density = critical density today then m ev c No experimental signals yet a chapter 7 astro-particle physics

26 Most popular candidates for Cold Dark Matter WIMPS - INTRODUCTION chapter 7 astro-particle physics

27 summary up to now: LCDM model dark baryonic 4% Neutrino HDM <1% cold dark matter 18% Universe is flat : k=0 luminous Radiation energy density 1% <1% today is negligible Dominated by vacuüm energy density = dark energy 18% Most of dark matter is cold cold dark matter (CDM) is of unknow type fi candidates for nonbaryonic cold dark matter from particle physics dark energy 76% 5 ( ) ( ) ( ) Ω Ω 0 0 Ω Λ K Ω =Ω + Ω +Ω = 0.24 m Bar ν HDM CDM chapter 7 astro-particle physics r

28 Axions Non-baryonic CDM candidates To reach density of order ρ c their mass must be very small mc No experimental evidence yet a ev Most popular candidate for CDM : WIMPs Weakly Interacting Massive Particles present in early hot universe stable relics of early universe Cold : Non-relativistic at time of freeze-out Weakly interacting : conventional weak couplings to standard model particles - no electromagnetic or strong interactions Massive: gravitational interactions (gravitational lensing ) Astro-particle physics 28

29 Massive neutrinos: WIMP candidates standard neutrinos have low masses contribute to HDM Massive standard d neutrinos up to M Z /2 = 45GeV/c 2 are excluded d by LEP: there are only 3 standard neutrino families Non-standard neutrinos in models beyond standard model Neutralino χ = Lightest SuperSymmetric Particle (LSP) in R- parity conserving SuperSymmetry (SUSY) theory Lower limit from accelerators ª 40 GeV/c 2 Stable particle survived from primordial era of universe Other SUSY particles: sneutrinos, gravitinos, axinos Kaluza-Klein states from models with universal extra dimensions Astro-particle physics 29

30 Cross sections and abundances -1 Neutralinos as CDM: non-relativistic at freeze-out 2 Mc kt M T Boltzman gas 3 2 M MT T = e number density 2π ( ) y N T Freeze-out when annihilation rate < expansion rate H ( ) W = N σ v H t freeze out + + χ + χ f + f, W + W, e + e,... Cross section s depends on SUSY parameters still unknown s(wimp annihilation) ª s(weak interactions) by construction Astro-particle physics 30

31 Cross sections and abundances -2 Weak interactions Rewrite expansion rate Freeze-out condition σ v H G M F 2 1 * 2 2 ( ) g T = M ( f = csts) ( ) T 2 PL M GF MT e M ft M 2 M PL Solve for P = M c 2 /kt M χ = 1GeV P = 20 c P 25 at freeze-out Mχ = 100GeV P= 30 Neutralino number density today T 0 = 2.73K ( fr out ) σ ( fr out ) N T v H T N ( 0) = N( Tfr out ) R R 3 3 ( T) 0 ( ) 0 3 ( T ) ( 2 0 Tfr out Tfr out MPL ) Astro-particle physics 31 σ v

32 Cross sections and abundances -3 Energy density today PT ρ χ = M χ N ( 0) M σv σv Ω = χ ρ χ ρ c 10 σv 25 PL cm s GeV s 1 Velocity of relic neutralinos at freeze-out from kinetic energy kt v ( ) 1 2 Mv = v c 2 2 c P For Ω 35 2 χ = 1 σ ( χ + χ X) 10 cm O ( pb ) O(weak interactions) fi weakly interacting particles can make up cold dark matter with ª correct abundance Astro-particle physics 32

33 Expected mass range: GeV-TeV Assume WIMP interacts weakly and is non-relativistic at freeze-out Which mass ranges are allowed? Cross section for WIMP annihilation vs mass fi abundance vs mass W HDM neutrinos CDM WIMPs 1) s = 4M < M σ s M χ W χ 2 2 2) s = 4Mχ > M W σ Ω 1 σ 1 1 s M 2 χ M WIMP (ev) chapter 7 astro-particle physics

34 Neutralino is good candidate for cold dark matter SUSY = extension of standard model at high energy SUPERSYMMETRY chapter 7 astro-particle physics

35 10 TeV GeV LHC - LEP chapter 7 astro-particle physics

36 SuperSymmetry -1 Gives a unified picture of matter (quarks and leptons) and interactions (gauge and Higgs bosons) Introduces symmetry between fermions and bosons Q fermion = boson Q boson = fermion allows a description of quantum gravity Fills the gap between electroweak and GUT scale 2 MW 10 GeV 17 = PL 10 GeV M Solves the hierarchy problem: divergence of radiative corrections to Higgs mass Provides a dark matter canndidate Astro-particle physics 36

37 SuperSymmetry -2 Need to introduce new particles: supersymmetric particles Associate to all SM particles a superpartner with spin ±1/2 (fermion-boson) fi sparticles Masses of SUSY particles are above ~40 GeV/c2 from negative searches at LEP, HERA and Tevatron minimal SUSY: minimal supersymmetric extension of the SM lowest nb of parameters Parameters - masses, couplings - must be determined from experiment Supersymmetry is broken at electroweak scale Astro-particle physics 37

38 The new particle table Particle table (arxiv:hep-ph/ v2) p Astro-particle physics 38

39 Unification of the couplings Unification of gauge couplings at M U ª GeV α 1 = α em α 2 = α weak α 3 = α strong Astro-particle physics 39

40 neutralinos - 1 Supersymmetric partners of gauge bosons (bino, wino, higgsinos) mix to neutralino mass eigenstates Lightest neutralino = mixing of 4 fields χ = χ = N B + N W + N H + N H Introduce R-parity quantum number f(baryon number B, lepton nb L, spin s) SM particles: R = 1 and sparticles: R = -1 R ( ) 2 1 B L s In R-parity conserving models Lightest Supersymmetric Particle (LSP) is stable In decay of sparticles at least 1 SUSY particle is produced LSP = lightest neutralino fi dark matter candidate Astro-particle physics 40

41 neutralino density vs mass Allowed variation of neutralino density as function of mass R-parity conserving SUSY Scan over 7- dimensional SUSY parameter space Expected mass range 50GeV few TeV W c h 2 W=[ ] Neutralino mass (GeV) Astro-particle physics 41

42 Detection of neutralinos = typical WIMP Difficult path to discovery WIMP DETECTION chapter 7 astro-particle physics

43 three complementary strategies Astro-particle physics 43

44 Production at colliders Controlled production in particle collisions Searches at LEP, HERA and Tevatron were negative but allowed to exclude regions of SUSY parameter space ass (G GeV) lino m Neutra chapter 7 astro-particle physics

45 Direct detection of WIMPs in MW Detectors to measure interaction of WIMPs from halo of Milky Way in matter Assume galaxy with dark halo Energy density in galactic halo much larger than on average in universe (gravitational ti effects in galaxy) density ρ χ 3 0.3GeV cm WIMP velocity today O(galactic objects) v 10 c= 270 kms χ 3 1 chapter 7 astro-particle physics

46 Direct detection principle Detector on Earth traverses wind of dark matter in galaxy halo WIMPs interact in detector weak interaction! Very low rate Measure recoil spectrum (N or X) in detector t χ + N χ + N χ + N χ + X elastic scattering inelastic scattering Recoil energy < 50 kev Need to measure very small effects Challenges: low rate Æ large detector very small signal Æ low threshold Low background : protect against cosmic rays, radioactivity, Astro-particle physics 46

47 Expected rates Cross sections for WIMP-proton interaction expected from allowed SUSY parameter space 44 2 σ ( χp) 10 cm 8 = 10 pb Rate of interaction ρ R N χ M χ σ χ p chapter 7 astro-particle physics

48 Example: XENON m under mountain in Gran Sasso tunnel (Italy) : lower rate of cosmic background filtered with muon veto counters Sensitive core =100kgliquid Xenon at -106 C Pure materials low radioactivity Measure signal from ionisation i and scintillation light produced d during recoil of nucleon Double signal helps against fake events Started data taking in 2009 chapter 7 astro-particle physics

49 Annual and diurnal modulation Annual modulations due to movement of solar system in galactic WIMP halo 30% effect Diurnal modulations due to Earth rotation 2% effect Observed by DAMA not confirmed by other experiments chapter 7 astro-particle physics

50 DAMA/LIBRA experiment Sensitive to recoil energies of 2-6 kev Measure scintillation light from nuclear recoil Data from ~5 years Observe modulation of 1 year (full curve) with phase of days chapter 7 astro-particle physics

51 Indirect detection of WIMPs Search for signals of annihilation of WIMPs in the Milky Way halo: antiparticles, gamma rays, neutrinos Expect accumulation near galactic centre due to gravitational attraction chapter 7 astro-particle physics

52 Neutrino signals Expect WIMPs to accumulate in heavy objects like Sun ρ χ χ velocity distribution Earth Sun σ cν ν μ ν int. G capture qq μ Detector G annihilation χχ ll ν ± W, Z, H chapter 7 astro-particle physics μ

53 Neutrino detection South Pole station Cherenkov light pattern emitted by the muon is registered by an array of photomultiplier tubes (PMT) 3km ice la ayer Photomultiplier tubes µ * ν μ 53

54 Signal and background BG A few 1000 atmospheric neutrinos per year from northern hemisphere signal Max. a few neutrinos per year from WIMPs BG ~10 9 atmospheric muons per year from southern hemisphere 54

55 Icecube observations One year of data taken with 25% of detector in 2007 Search for neutrinos from WIMP annihilation in the Sun No significant signal found Angle y between reconstructed neutrino and Sun Distribution compatible with atmospheric background IC Signal region cos(ψ) chapter 7 astro-particle physics

56 What did we learn so far? Absence of signal in direct detection experiments and in neutrino detectors yields upper limit on WIMP-proton cross section Sensitivities not yet at level needed to test SUSY models Direct search experiments indirect search neutrinos Theoretical SUSY predictions Allowed by other experiments Expect 10-3 pb or lower Full IceCube Neutralino mass (GeV) chapter 7 astro-particle physics

57 Antiparticles from dark matter? Antimatter in sky = secondary particles produced by primary cosmic rays = shaded area Excess in positron fraction could be dark matter annihilation products in contradiction with antiproton results chapter 7 astro-particle physics

58 Conclusions Strong observational evidence for dark matter in universe at all scales Known particles explain only maximum 5% of dark matter baryons, neutrinos Nature of dark matter still unknown Most popular candidates are Weakly Interacting Massive Particles Discovery of dark matter particles is expected in coming years at LHC and in direct and indirect search experiments chapter 7 astro-particle physics