Lecture 19 Nuclear Astrophysics. Baryons, Dark Matter, Dark Energy. Experimental Nuclear Physics PHYS 741

Transcription

1 Lecture 19 Nuclear Astrophysics Baryons, Dark Matter, Dark Energy Experimental Nuclear Physics PHYS 741 References and Figures from: - Haxton, Nuclear Astrophysics - Basdevant, Fundamentals in Nuclear Physics 1

2 Pheno Seminar this Friday Friday, November 21st, 2008 Phenomenology Seminar Methods to Detect the Cosmic Neutrino Background Time: 2:30 pm Place: 5280 Chamberlin Hall Speaker: Bob McElrath, CERN 2

3 The First Three Minutes: BBN period of Big Bang Nucleosynthesis 3

4 Early Universe kt ~ 10 MeV e-,e+, neutrinos in equilibrium kt ~ 3 MeV falling out of equilibrium kt > 1 MeV n, p are free and in chemical equilibrium n/p ratio at end of this epoch is ~ MeV > kt > 60 kev n decay freely, half of neutrons decay epoch of decoupling duration of this period ~ 3 min n/p ratio ~ 0.17 kt ~ 60 kev (-> nucleosynthesis) network of reactions kt ~ 30 kev (-> freezeout of nuclear reactions) 4

5 n/p Ratio as a Function of Temperature n/p ratio 5

6 He Formation 6

7 Abundances of Light Elements most neutrons are incorporated into 4 HE - Deuterium peaks around 100 seconds after the Big Bang, and is then rapidly swept up into helium nuclei. after kt~30kev nuclear reactions are frozen - A very few helium nuclei combine into heavier nuclei giving a small abundance of Li 7 coming from the Big Bang. Note: - H 3 decays into He 3 with a 12 year half-life so no H 3 survives to the present - Be 7 decays into Li 7 with a 53 day half-life and also does not survive. 7

8 Important Nuclei for BBN primordial nucleosynthesis stops a A=7 Note: production of heavy elements occurs in stars where triple-alpha reaction takes place 3 4 He -> 12 C 8

9 Key Factors in BBN presence of neutrons BBN has lots of neutrons available n + p can combine low baryon-photon ratio delays nucleosynthesis dissociates any nuclei that are produced until we reach kt< 100keV low baryon-neutrino ratio important when nucleons are free νen -> e - p can change neutrons into protons limited amount of time (~ 3min) time from quark-gluon plasma to end of BBN ~ 3min 9

10 What are the characteristics of todayʼs Universe? 10

11 What are the characteristics of todayʼs Universe? - expansion of Universe - visible Universe - baryons - dark matter - photons - neutrinos - the vacuum 11

12 period of Big Bang Nucleosynthesis 12

13 Milestones in Early Universe at T < 100 kev deuterium formation, followed by BBN n+p d+γ at T < 1 ev (380,000 yrs) photons decouple, cannot break up atoms no more free charges to scatter photons Universe becomes transparent p+e - H+γ 13

14 Cosmic Microwave Background 14

15 Occupants of the Universe all data from WMAP except for - photon density (COBE) - lower limit of neutrino density (oscillation data) 15

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17 Hubble Diagram - velocities determined by galaxy redshifts - distances determined by a variety of methods (e.g. SN of known luminosity gives phi=l/4pir^2) 17

18 Hubble Diagram 18

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20 Rotation Curve of Galaxies: Evidence for Dark Matter 20

21 Rotation Curve of Galaxies: Evidence for Dark Matter 21

22 Rotation Curve of Galaxies: Evidence for Dark Matter 22

23 Cosmic Microwave Background photons are most abundant particles in the Universe 23

24 Cosmic Microwave Background Blackbody Radiation nearly perfect thermal spectrum 24

25 Observed Spectrum of Cosmic Microwave Background shorter wavelength measurements from balloons, satellites, etc (atmosphere is opaque) 25

26 Observed Spectrum of Cosmic Microwave Background 26

27 CMB Multipole Spectrum temperature anisotropies at 10-5 level 27

28 Dark Matter in the Power Spectrum first acoustic peak in the CMB is sensitive to matter density: ρm 28

29 Baryons in the Power Spectrum 29

30 Relic Neutrinos at T ~ 1 MeV (~ 1 sec) neutrinos decouple relic neutrino spectrum left over at T < 1 ev (380,000 yrs, recombination time) photons decouple, cannot break up atoms no more free charges to scatter photons Universe becomes transparent p+e - H+γ 30

31 Neutrinos and Cosmology We see imprints of neutrino mass in the structure of todayʼs Universe very early universe big bang nucleosynthesis late time structure formation WMAP large-scale structure enhanced early ISW effect effect on structure formation Neutrinos that are more massive cause more clustering on large scales. Even small neutrino mass influences power spectrum of galaxy correlations 31

32 Occupants of the Universe all data from WMAP except for - photon density (COBE) - lower limit of neutrino density (oscillation data) 32

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35 Heavy Elements: 0.03% Ghostly Neutrinos: ~0.3% Stars: 0.5% Matter in the Universe Free Hydrogen and Helium: 0.4% Dark Energy: 70% Dark Matter: 25% 35

36 Formative Events in the Evolution of the Universe 36

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