Astro-particle-physics

Transcription

1 Astro-particle-physics An operational definition: Astro-particle-physics The intersection of elementary particle physics (microprocesses) and astro-physical phenomena, including cosmology.

2 Outline of Lecture Matter and curvature of space-time Standard Cosmology Observational data Inflation Evidence for dark matter Searching for dark matter

3 Curvature

4 Comments Einstein field eqn s describe local effects of curvature (e.g. gravitational lensing, deflection of starlight) and global structure of plausible (and implausible?) universes. Note: resemblance to e.g. Maxwell s equations with a source term (Stress-energy tensor) and a field term (Curvature)

5 Einstein Field Equation Cosmological constant G = 8π T + Λg µν µν µν Curvature term Stress-energy tensor

6 Stress Energy Tensor β dx () t T x p t x x t αβ α n 3 ( ) = n ( ) δ ( n( )) n dt Relativistic hydrodynamic assumption T = ( ρ + p) U U + pg αβ α β αβ α β ξ ξ = µ ν η x x pressure density 4 velocity g p ρ U α µν αβ

7 Stress-Energy Tensor At first difficult to imagine objects (e.g. galaxies) as a hydrodynamic fluid, but this approximation is well merited. Components of vacuum energy, normal matter, photons, mysterious other terms. Work of cosmologists is to evaluate implication of tweaking of S-E tensor via introduction of new forms of matter

8 Curvature I α β ξ ξ g = µ ν η x x λ 2 α λ x ξ Γ = ξ x x η ξ x µν αβ µν α µ ν αβ α µ = diag( 1,1,1,1) Freely falling coord Any coord

9 Curvature II Curvature scalar Ricci tensor Gµν = Rµν g µν R 1 2 R R µκ R = g R R = λ µν µλκ µκ Γ λ λ λ µν µκ η λ η λ µλκ = +ΓµνΓ κ ν κη Γµ kγνη x Γ x Curvature Tensor

10 Global Metrics Certain global metrics will describe a cosmology that will satisfies the Einstein- Field Equations. Many have odd features. The standard cosmology is the Robertson- Walker metric Imbedded expanding 3-sphere ( expanding balloon analogy)

11 Robertson-Walker Metric dr dτ = dt R () t + r dθ + r sin θdφ 2 1 kr dτ Proper time interval Rt () k "Radius of Universe" Sign of curvature (+1=closed, 0=flat, - 1=open)

12 FRW Model Describes observational data well No guarantees that the global topology is as simple as the FRW metric implies (e.g. toroidal universes can you see the back of your head, multiply connected etc) Simple treatment of Stress-Energy tensor Concept of a co-moving inertial frame (e.g. w.r.t. cosmic microwave background) Regions can be out of causal contact

13 FRW Stress Energy Terms µ Tν = diag( ρ, p, p, p) ( pt ( ), ρ( t)) 1st law of thermodynamics d R pd R 3 3 ( ρ ) = ( ) 1 ( p= ρ) ρ R 3 3 ( p= 0) ρ R 4 ( p= ρ) ρ ( const.) Radiation Matter Vacuum energy

14 FRW Universe Early universe was radiation dominated With no vacuum energy, adolescent and late universe are matter dominated With inflation (see ahead) very early period where vacuum energy dominated the SE tensor

15 FRW Universe G 00 Use RW metric to solve Einstein field eqn.. 2 R k 8π G + = ρ 2 2 R R 3 Friedmann Equation. R R k H ρ = 3 /8π 1 Ω 1 ρ ρc H πg H R H G Ω ρc 2 3 /8 Define Hubble parameter Recast Friedmann eqn. Critical Density

16 Relation to curvature Ω> 1 Ω= 1 Ω< 1 Closed Flat Open Density of universe relative to critical density relates to curvature Universe is old, means that Ω cannot be too large or density was too high

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19 Epochs of FRW Universe Planck Era Wave function of the universe(?) (Inflation symmetry transition) Baryogenesis Nucleosynthesis Neutralization ( freeze out ) Star/galaxy formation

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21 Particle Connections The early universe is, in a sense, a laboratory for particle interactions Baryogenesis CP violation (GUT scale) Inflation symmetry breaking Overall mass supersymmetry (TeV scale) Nuclear synthesis Radiation - interaction with matter before freeze-out Remaining vacuum energy (?) present

22 What can we observe? Red shift versus distance (R(t)-effectively) Cepheids, SN, sizes, luminosity of galaxies Age of the universe Radioactive clocks (U 238 to U 235 ratio) Stellar populations Cosmic microwave background radiation Structure formation (distribution of mass) Nuclear abundances

23 Uranium Isotopic Content U U 1.71 Production abundances U U Observed abundances t = ln P U U ln U U 1 1 τ τ o 6.6Gyr

24 Red Shift Versus Distance The farther away you look, the more redshift one sees. Effects of Recessional velocity associated with expansion of universe Looking backward in time

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26 Age/Mass/Curvature Combination overconstrains FRW model Depending on test Gyr=age (14.37 Gyr?) Hubble constant measurements, Ω o =1 (flat) Contributions to Ω Luminous matter Dark baryons (jupiters ) Halos Unclustered Vacuum energy

27 Cosmic Distance Ladder Parallax near star distances Kinds of stars, luminosity, spectrum Cepheids variable stars with well defined periodicity/luminosity Supernovae universal brightness curve SZE effect using cosmic microwave background as standard candle

28 Mass Contributions(Circa 1989) Ω LUM 0.01 ΩHalo Ω Ωb Ω unclustered = 0.8 Luminous LUM Baryonic Assuming critical density Halo Smooth at Mpc distance scales

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30 Recent Fits 70% dark energy 24% dark matter 4% baryonic matter Mainly from Supernova survey (Perlmutter et al.) New projects will help elucidate this

31 Dark Energy Non-zero vacuum energy contributions to FRW universe can produce unusual effects Inflation acceleration of Hubble Expansion Recent surveys of redshift versus distance sets scale is suggestive of a vacuum energy contribution (equivalent to Λ term in Einstein eqn) Ω M versus Ω Λ

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34 The Sunyaev-Zel'dovich Effect Future path to elucidating the Hubble curve CMB photons scatter from ionized electrons in galaxy, giving a measure of temperature, and can be compared to redshift measurements to get larger distance measurements Existence proof by J. Carlstrom (U. Chicago)

35 SZE effect

36 Isotropy Problem At time of neutralization, 10 5 causally disconnected regions CMB uniform to about 1 part in 10 4 (most angular scales, subtracting out earth s motion wrt co-moving frame) Finite horizon makes it impossible to achieve this isotropy

37 Other unresolved issues From Grand-unification, theories predict a density of monopoles, cosmic strings, etc, which is not observed Flatness, Ω = 1 (identically?)

38 Inflation After GUT symmetry breaking a phase transition associated with a Higgs-like potential creates a very rapid expansion Starts at sec, lasts sec Spreads out universe by factor of Preserves uniformity after causal disconnect Spreads out monopoloes Gives flat universe Variation: chaotic inflation

39 Higgs Potential Higgs Potential V( φ) = m φ + λφ 2 4 Minima of Higgs potential σ ± =± 2 m λ

40 Inflationary potential V ( φ) H φ i φ e σ

41 Dark Mass Evidence Ω=1 discrepancy Gravitational lensing Supercluster velocities (Virgo infall) Galactic rotation curves Origins High velocity massive particles Large population of dark galaxies Significant vacuum energy contributions

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44 Dark Mass Candidates Must be weakly interacting (broad distribution, no radiation damping) Neutrinos not favored Axions associated with strong CP problem perhaps Supersymmetric matter Neutralinos

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47 Background χ 0 Nucleus Recoils E r v/c 10-3 Dense Energy Deposition v/c small; Bragg Neutrons same, but σ higher - shield γ Electron Recoils E r v/c 0.3 Sparse Energy Deposition Density/Sparsity Basis of Discrimination

48 Dark Matter Detection Velocity of earth wrt WIMP cloud Whatever that is!!! 300 km/sec minimum 100 GeV scale massive critters Backgrounds are the devil!!! Cosmics Residual radiation in materials CDMS (cryo dark matter search) Solid state detectors measure both phonons and ionization loss of recoil nuclei

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50 The Experiments CDMS - Ge/Si, measure ionization (Q) and heat/phonons (P) Recoil/γ discrimination: Q/P 2 Detector Types, 2 sites! Updated Result ZEPLIN 1 - Liq Xe, measure scintillation Recoil/γ discrimination: Pulse Shape in Time 2 more ZEPLIN s - add ionization New Result DRIFT - CS 2, measure ionization (Q) Recoil/γ discrimination: Spatial Distribution of Q Directionality

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52 Nucleus Recoils E r A 2 M WIMP =100 GeV σ=10-42 cm 2 /nucleon Silicon, Sulphur Germanium Iodine, Xenon Slope: Maxwell-Boltzmann WIMPs in Galaxy Diffraction off Nucleus χ 0

53 CDMS Data Inner: 12 kg-d Calibration 1334 Photons (external source) 233 Electrons (tagged contamination) Inner Ionization Electrode Outer Ionization Electrode Shared: 4.4 kg-d 13 nucl. recoil 616 Neutrons (external source) Shallow: Neutrons 10 nucl. recoil

54 WIMP/nucleon σ cm Exper. CDMS DAMA Theory SUSY, various constraints including Big Bang

55 Not covered here CMB (Scott) Nuclear abundances (Scott) CP violation, baryogenesis (Kate)

56 Conclusions/caveats It would be interesting to dig up this talk in 10 years and see how things stand up Will Dark Energy Survive? Will we find WIMP s or understand dark matter? Will symmetry breaking shed light on inflation? What does a TeV scale Planck scenario imply? Will FRW models still be the standard?