Document Sample

Astro-particle-physics An operational definition: Astro-particle-physics The intersection of elementary particle physics (microprocesses) and astro-physical phenomena, including cosmology. 21 Aug 03 John Huth, Harvard NESPR 02 Outline of Lecture • Matter and curvature of space-time • “Standard Cosmology” • Observational data • Inflation • Evidence for dark matter • Searching for dark matter 21 Aug 03 John Huth, Harvard NESPR 02 Curvature 21 Aug 03 John Huth, Harvard NESPR 02 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) 21 Aug 03 John Huth, Harvard NESPR 02 Einstein Field Equation Cosmological constant G 8 T g Curvature term Stress-energy tensor 21 Aug 03 John Huth, Harvard NESPR 02 Stress Energy Tensor dxn (t ) 3 T ( x) pn (t ) ( x xn(t )) n dt Relativistic hydrodynamic assumption T ( p )U U pg g x x p pressure density U 4 velocity 21 Aug 03 John Huth, Harvard NESPR 02 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 21 Aug 03 John Huth, Harvard NESPR 02 Curvature I g x x x 2 x x diag (1,1,1,1) Freely falling coord x Any coord 21 Aug 03 John Huth, Harvard NESPR 02 Curvature II Curvature scalar tensor Ricci 1 G R g R 2 R R R g R R k x x Curvature Tensor 21 Aug 03 John Huth, Harvard NESPR 02 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) 21 Aug 03 John Huth, Harvard NESPR 02 Robertson-Walker Metric dr 2 2 d dt R (t ) 2 2 2 r d r sin d 2 2 2 2 1 kr 2 d Proper time interval R (t ) "Radius of Universe" Sign of curvature k (+1=closed, 0=flat, - 1=open) 21 Aug 03 John Huth, Harvard NESPR 02 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 21 Aug 03 John Huth, Harvard NESPR 02 FRW Stress Energy Terms T diag ( , p, p, p ) ( p (t ), (t )) 1st law of thermodynamics d ( R 3 ) pd ( R 3 ) 1 ( p ) R 4 Radiation 3 ( p 0) R 3 Matter ( p ) (const.) Vacuum energy 21 Aug 03 John Huth, Harvard NESPR 02 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 21 Aug 03 John Huth, Harvard NESPR 02 FRW Universe G 00 Use RW metric to solve Einstein field eqn. . R 2 k 8 G Friedmann R2 R2 3 Equation . Define Hubble R H parameter R Recast Friedmann eqn. k 1 1 H 2 R 2 3H 2 / 8 G c c 3H 2 / 8 G Critical Density 21 Aug 03 John Huth, Harvard NESPR 02 Relation to curvature • Density of universe relative to critical 1 Closed density relates to curvature 1 Flat • Universe is old, means 1 Open that Ω cannot be too large or density was too high 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 Epochs of FRW Universe • Planck Era – Wave function of the universe(?) • (Inflation – symmetry transition) • Baryogenesis • Nucleosynthesis • Neutralization (“freeze out”) • Star/galaxy formation 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 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 21 Aug 03 John Huth, Harvard NESPR 02 What can we observe? • Red shift versus distance (R(t)-effectively) – Cepheids, SN, sizes, luminosity of galaxies • Age of the universe – Radioactive clocks (U238 to U235 ratio) – Stellar populations • Cosmic microwave background radiation • Structure formation (distribution of mass) • Nuclear abundances 21 Aug 03 John Huth, Harvard NESPR 02 Uranium Isotopic Content 235U 238 U 1.71 Production abundances 235 U 238 U 0.00732 Observed abundances ln 235U 238 U P ln 235U 238 Uo t 6.6Gyr 238 1 1 235 21 Aug 03 John Huth, Harvard NESPR 02 Red Shift Versus Distance • The farther away you look, the more red- shift one sees. • Effects of – Recessional velocity associated with expansion of universe – Looking “backward in time” 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 Age/Mass/Curvature • Combination overconstrains FRW model • Depending on test – 10-20 Gyr=age (14.37 Gyr?) • Hubble constant measurements, Ωo=1 (flat) • Contributions to Ω – Luminous matter – Dark baryons (jupiters…) – Halos – Unclustered – Vacuum energy 21 Aug 03 John Huth, Harvard NESPR 02 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” 21 Aug 03 John Huth, Harvard NESPR 02 Mass Contributions(Circa 1989) LUM 0.01 Luminous Halo 0.1 10LUM Halo b 0.015 Baryonic Assuming critical density unclustered 0.8 Smooth at 10-30 Mpc distance scales 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 Recent Fits • 70% “dark energy” • 24% “dark matter” • 4% baryonic matter • Mainly from Supernova survey (Perlmutter et al.) • New projects will help elucidate this 21 Aug 03 John Huth, Harvard NESPR 02 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) • ΩM versus ΩΛ 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 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) 21 Aug 03 John Huth, Harvard NESPR 02 SZE effect 21 Aug 03 John Huth, Harvard NESPR 02 Isotropy Problem • At time of neutralization, 105 causally disconnected regions • CMB uniform to about 1 part in 104 (most angular scales, subtracting out earth’s motion wrt co-moving frame) • Finite horizon makes it “impossible” to achieve this isotropy 21 Aug 03 John Huth, Harvard NESPR 02 Other unresolved issues • From Grand-unification, theories predict a density of monopoles, cosmic strings, etc, which is not observed • Flatness, Ω = 1 (identically?) 21 Aug 03 John Huth, Harvard NESPR 02 Inflation • After GUT symmetry breaking – a phase transition associated with a Higgs-like potential creates a very rapid expansion – Starts at 10-34 sec, lasts 10-32 sec – Spreads out universe by factor of 10-43 • Preserves uniformity after causal disconnect • Spreads out monopoloes • Gives flat universe • Variation: chaotic inflation 21 Aug 03 John Huth, Harvard NESPR 02 Higgs Potential Higgs Potential 1 1 V ( ) m 2 2 4 2 4 Minima of Higgs potential m2 21 Aug 03 John Huth, Harvard NESPR 02 Inflationary potential V ( ) H i e 21 Aug 03 John Huth, Harvard NESPR 02 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 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 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 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 Background Nucleus Electron Er Recoils Recoils Er v/c 10-3 v/c 0.3 Dense Energy Deposition v/c small; Bragg Sparse Energy Deposition Neutrons same, but 1020 higher - shield 0 Density/Sparsity Basis of Discrimination 21 Aug 03 John Huth, Harvard NESPR 02 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 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 The Experiments CDMS - Ge/Si, measure ionization (Q) and heat/phonons (P) Recoil/ discrimination: Q/P 2 Detector Types, 2 sites! Updated Result ZEPLIN 1 - Liq Xe, measure scintillation Recoil/ discrimination: Pulse Shape in Time 2 more ZEPLIN’s - add ionization New Result DRIFT - CS2, measure ionization (Q) Recoil/ discrimination: Spatial Distribution of Q Directionality 21 Aug 03 John Huth, Harvard NESPR 02 21 Aug 03 John Huth, Harvard NESPR 02 MWIMP=100 GeV 10-42 cm2/nucleon A2 Silicon, Sulphur Nucleus Germanium Recoils Iodine, Xenon Er Slope: Maxwell-Boltzmann WIMPs in Galaxy Diffraction off Nucleus 0 21 Aug 03 John Huth, Harvard NESPR 02 CDMS Data Inner: 12 kg-d Calibration Inner Ionization Electrode 13 nucl. recoil 1334 Photons (external source) Outer Ionization Electrode Shared: 4.4 kg-d 233 Electrons (tagged contamination) 616 Neutrons (external source) Shallow: 10 nucl. recoil 21 Aug 03 Neutrons John Huth, Harvard NESPR 02 WIMP/nucleon 10-42 cm Exper. CDMS DAMA Theory SUSY, various constraints including Big Bang 21 Aug 03 John Huth, Harvard NESPR 02 Not covered here • CMB (Scott) • Nuclear abundances (Scott) • CP violation, baryogenesis (Kate) 21 Aug 03 John Huth, Harvard NESPR 02 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? 21 Aug 03 John Huth, Harvard NESPR 02

DOCUMENT INFO

Shared By:

Categories:

Tags:

Stats:

views: | 0 |

posted: | 11/26/2012 |

language: | English |

pages: | 56 |

OTHER DOCS BY yurtgc548

Docstoc is the premier online destination to start and grow small businesses. It hosts the best quality and widest selection of professional documents (over 20 million) and resources including expert videos, articles and productivity tools to make every small business better.

Search or Browse for any specific document or resource you need for your business. Or explore our curated resources for Starting a Business, Growing a Business or for Professional Development.

Feel free to Contact Us with any questions you might have.