The expanding universe. Lecture 2

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1 The expanding universe Lecture 2

2 Expanding universe : content part 1 : ΛCDM model ingredients: Hubble flow, cosmological principle, geometry of universe part 2 : ΛCDM model ingredients: dynamics of expansion, energy density components in universe Part 3 : observation data redshifts, SN Ia, CMB, LSS, light element abundances ΛCDM parameter fits Part 4: radiation density, CMB Part 5: Particle physics in the early universe, neutrino density Part 6: matter radiation decoupling Part 7: Big Bang Nucleosynthesis Part 8: Matter antimatter asymmetry y Expanding Universe lect 2 2

3 Universe is flat k=0 Last lecture Expansion dynamics is described by Friedman Lemaître 2 equation 2 2 R () t 8π G ρn kc H( t) = tot( ) 2 R t ( ) 3 ( R ( t ) ) Cosmological redshift R( t0 ) t 1 z z( t0 ) 0 z( t 0) R ( t ) Closure parameter + = = = = ρt( ) Ω 3H ( t ) = ρ ( t ) 0 ( t) Expansion rate as function of redshift HΩtΩρ c t2 c t = GeV m πg = 8 N 22 H () t = 0 m( )( ) 3 r1+ z + 0( )( 1+ z) 4 + Λ0( ) + k0( )( 1+ z) 2 0Expanding Universe lect 2 t ΩtΩ3

4 Todays lectur re Ω CDM Part 5 > TeV CDM Rubakov Expanding Universe lect 2 4

5 Todays lectur re ( ) ( ) NB part 8 Ω CDM Part 5 Nanti B > TeV CDM Rubakov Expanding Universe lect 2 5

6 Todays lectur re Ω neutrino Part 5 ( ) Nanti ( B ) NB part 8 Ω CDM Part 5 CDM Rubakov Expanding Universe lect 2 6

7 Todays lectur re Ω baryons Part 7 Ω neutrino Part 5 ( ) Nanti ( B ) NB part 8 Ω CDM Part 5 CDM Rubakov Expanding Universe lect 2 7

8 Ω rad Part 4&6 Todays lectur re Ω baryons Part 7 Ω neutrino Part 5 ( ) Nanti ( B ) NB part 8 Ω CDM Part 5 CDM Rubakov Expanding Universe lect 2 8

9 Part 4 radiation component - CMB Physics of the Cosmic Microwave Background Present day photon density

CMB in Big Bang model Matter photons are released

equilibrium Photonsdecouple/freeze out out During

uniform γ radiation which behaves like a black

10 CMB in Big Bang model Matter photons are released Univ Oregon Baryons/nuclei and photons in thermal equilibrium Photonsdecouple/freeze out out During expansion they cool down Expect to see today a uniform γ radiation which behaves like a black body radiation Expanding Universe lect 2 10

CMB discovery in 1965 discoveredd in 1965 by

for radio emissionfrom MilkyWay Observed a uniform

not be explained by stars, radio galaxies etc Use

due to absorption of mmwaves in atmosphere Observed

11 CMB discovery in 1965 discoveredd in 1965 by Penzias and Wilson (Bell lb) labs) when searching for radio emissionfrom MilkyWay Observed a uniform radio noise from outside the Milky Way This could not be explained by stars, radio galaxies etc Use Earth based observatory: limited to cm wavelengths due to absorption of mmwaves in atmosphere Observed spectrum was compatible with black body radiation with T = (3.5 ±1) K Obtained the Nobel Prize in 1978 ( Expanding Universe lect 2 11

COBE : black body spectrum To go down to mm wavelengths: put instruments on satellites COBE = COsmic Background Explorer (NASA) satellite observations in 1990s: mm

galactic plane After subtraction of dipole and away from galacticcentre: centre: radiation was uniform up to 0.005% Has perfect black body spectrum with T = 2.735±0.

12 COBE : black body spectrum To go down to mm wavelengths: put instruments on satellites COBE = COsmic Background Explorer (NASA) satellite observations in 1990s: mm wavelengths Large scale dipole anisotropy due to motion of solar system in universe, with respect to CMB rest frame v ( solar system) 300 km s Strong radio emission in galactic plane After subtraction of dipole and away from galacticcentre: centre: radiation was uniform up to 0.005% Has perfect black body spectrum with T = 2.735± K K (COBE 1990) Discovered small anisotropies/ripples over angular ranges Dq=7 2006Nobel prize to Smootand Mather for discovery of anisotropies Expanding Universe lect 2 12

13 CMB temperature map dipole ΔT smallll ripples i l on top t off Black Bl k Body B d radiation: di ti Expanding Universe lect 2 ΔT T T 10 3 O ( mk ) 10 5 O ( µk ) 13

14 COBE measures black body spectrum l=2mm Intensity Q 0.5mm Plancks radiation law for relativistic photon gas Black body with temperature T emits radiation with power Q at frequencies w Frequency n (cm 1 ) Q ω, T ( ) ω = 2πν = 4π c ω ω e k T Expanding Universe lect 2 14

15 COBE measures black body spectrum l=2mm Intensity Q 0.5mm CMB has perfect black body spectrum Fit of data of different observatoria to black body spectrum gives (pdg.lbl.gov, CMB) ( ) = ( ± ) ( max) 2mm T CMB λ = K Frequency n (cm 1 ) Or E = kt = mev Expanding Universe lect 2 15

16 radiation energy density vs time In our model the early universe is radiation dominated For flat universe Friedmann equation R 8π G 2 N = 2 R 3 energy density of radiation during expansion ρ rad ρ rad 1+ z R ( ) 4 4 Integration yields ρ 1 dρ R 8πG 4 4 N ρrad = = ρ dt R 3 rad c 2 t () = 2 3c 1 32π GN t Expanding Universe lect 2 16

17 CMB number density today 1 CMB photons have black body spectrum today Theyalsohad black body spectrum when CMB was created But! Temperature T in past was higher than today CMB = photon gas in thermal equilibrium Bose Einstein distribution : number of photons per unit volume in momentum interval g[p,p+dp] 2 γpdp n( p) dp= 2 g γ = number of 2 3 e E k π T 1 photon substates Black body Expanding Universe lect 2 17

18 CMB number density today 2 n N V γ = = γ g γ =2 n p dp ( ) n γ 1 kt = π c 3 T=2.725K n γ t0 = 411cm ( ) Expanding Universe lect 2 18

19 CMB energy density today ρ c 2 = E n p dp ( ) ρc π = ( kt ) 2 ( ) 3 π c 15 T=2.725K ρ t = M V rc ( t ) MeV m 2 3 ρ Ω ( ) r r t0 = = ρ ρ c Expanding Universe lect 2 19

20 CMB temperature vs time ρ rad c 2 = 2 3c 1 2 4( ) 4 γ 1 2 ρ radc = π kt πg t 2 15 π c 32 N g kt c MeV 1 = 3 T rad dom = 11 32π G g γ k 2 t t 2for t 0 = 14Gyr expect T CMB (today) ª 10K!!! BUT! COBE measures T = 2.7K Explanation??? Expanding Universe lect 2 20

21 Summary ( 1 ) 4 2 radiation ρ c + z ( 1 ) 3 2 matter ρ c + z 2 vacuum ρc cst ( 1 ) 2 curvature ρ c + z Expanding Universe lect1 21

22 Questions?

23 Part 5 particle physics in the early universe Radiation dominated universe From end of inflation to matter radiation decoupling From ~ 10 7 GeV to ev Physics beyond the Standard Model, SM, nuclear physics

24 Radiation domination era Planckera GUT era At end of inflation phase there is a reheating phase Relativistic particles are created td Expansion is radiation dominated Hot Big Bang evolution starts kt TeV Expanding Universe lect 2 24 t

25 Radiation domination era At end of inflation phase there is a reheating phase Relativistic particles are created td Expansion is radiation dominated Hot Big Bang evolution starts R Planck era GUT era t Expanding Universe lect 2 25

26 Radiation domination era Planckera GUT era kt Today s lecture TeV Expanding Universe lect 2 26 t

27 Planck mass Grand 1 TeV 100 ~ GeV Unification GeV ~ GeV LHC LEP Inflation period Expanding Universe lect 2 27

28 Today s lecture Planck mass Grand 1 TeV 100 ~ GeV Unification GeV ~ GeV LHC LEP Inflation period Expanding Universe lect 2 28

29 Relativistic particles Radiation dominated kt >> 100 GEV Expanding Universe lect 2 29

30 relativistic particles in early universe In the early hot universe relativistic fermions and bosons contribute to the energy density They are in thermal equilibrium at mean temperature T Fermion gas = quarks, leptons Fermi Dirac statistics (g f = nb of substates) ( ) n p dp g f 2 p dp = E 2 3 kt 2 π e 1 + boson gas = photons, W and Z bosons BoseEinstein statisticss n( p) dp π (g b = nb of substates) g b 2 p dp = E 2 3 kt 2 e Expanding Universe lect 2 30

31 relativistic particles in early universe Bosons and fermions contribute to energy density with ( ) n p dp 2 pdp g 2 = b p dp g E 2 3 kt 2 ( ) f n p dp= E π e kt 2 π e 1 + ρ 2 ρ c = E ( ) n p dp g( ( ) π ( ) = = + 15π c * * c t kt g g b g f * Expanding Universe lect 2 31

32 Degrees of freedom for kt > 100 GeV If we take only the known particles bosons spin per particle total t W+ W Z gluons photon H boson total bosons 28 fermions spin per particle total quarks antiquarks e,µ,τ neutrinos anti neutrinos total fermions Expanding Universe lect 2 32

33 Degrees of freedom for kt > 100 GeV bosons spin per particle total W+ W x 3 = 6 Z gluons x 2 = 16 photon H boson total bosons 28 fermions spin per particle total quarks ½ 3 (color) x 2 (spin) 6 x 3 x 2 = 36 antiquarks 36 e,µ,τ ½ 2 6 x 2 = 12 neutrinos LH 1 3 x 1 = 3 anti neutrinos RH 1 3 x 1 = 3 total fermions Expanding Universe lect 2 33

34 Degrees of freedom for kt > 100 GeV Assuming only particles from Standard Model of particle physics g = = * 7 Energy density in hot universe *( ) ( ) ρ* c t = π kt π c 2 g what happens if there were particles from theories beyond the Standard Model? Expanding Universe lect 2 34

35 For instance : SuperSymmetry At LHC energies and higher : possibly SuperSymmetry Symmetrybetween fermions and bosons Consequence is a superpartner for every SM particle ~ Double degrees of freedom g* Expanding Universe lect 2 35

36 Neutralino = Dark Matter? Neutral gaugino and higgsino fields mix to form 4 mass eigenstates 4 neutralinos no charge, no colour, only weak and gravitational interactions χ is Lightest t Supersymmetric Particle LSP in R parity conserving scenarios stable Massive : Searches at LEP and Tevatron colliders m ( ) χ 0 > 50 GeV c Expanding Universe lect 2 36

37 Neutralino = Dark Matter? Lightest neutralino may have been created in the early hot universe when >> ( χ ) 0 kt m c Equilibrium interactions e + e χ 0 + χ0 When kt is too low, neutralinos freeze out (decouple) e + e χ + χ e + e χ + χ 0 0 are non relativistic at decoupling = cold survive as independent population till today 0 0 the observed dark matter abundance today puts an upper limit on the mass (chapter 7) Ω <1 1 m χ 1 < 5 TeV c 2 CDM ( ) Expanding Universe lect 2 37

38 Questions?

39 COOLDOWN TO A FEW GEV Expanding Universe lect 2 39

40 Cool down from > TeV to kt ª GeV Start from hot plasma of leptons, quarks, gauge bosons, Higgs, exotic particles T rad dom Temperature decreases with time 1 2 Production of particles M stops when kt ~ << 1 t Mc For example, + + e + e W + W when s > 2MW = 160GeV p + p t+ t + X when > 2 = 346 s M GeV 23 some particles decay: W, Z, t.. τ ( W, Z) 10 Run out of heavy particles when kt<<100gev Expanding Universe lect 2 40 top s 2

41 Age of universe at kt few GeV Radiation dominated expansion since Big Bang T MV MeV 1 k rad dom = 12Calculate time difference relative to Planck t era Expanding Universe lect 2 41

42 Quarks form hadrons COOLDOWN TO kt 200 MEV Expanding Universe lect 2 42

43 A phase transition Quarks form hadrons Decay of particles with lifetime < µsec 200 MeV g* kt(gev) Expanding Universe lect 2 43

perturbative regime around Λ QCD α S 2 = = gstrong 1 ~ 4π b ln Q( 2 2 μ Q ) ln ( 2 2 μ CD) 0 μ ΛE T confinement Quarks cannot

44 Down to kt ª 200 MeV Phase transition from Quark Gluon Plasma (QGP) to hadrons Ruled by Quantum Chromo Dynamics (QCD) describing strong interactions Strong coupling constant is running : energy dependent From perturbative regime to non perturbative regime around Λ QCD α S 2 = = gstrong 1 ~ 4π b ln Q( 2 2 μ Q ) ln ( 2 2 μ CD) 0 μ ΛE T confinement Quarks cannot be free at distances of more than 1fm = m α t Λ = α s QCD 200MeV From fit to data When µ 200 MeV Expanding Universe lect 2 44

45 Colour confinement large distances Asymptotic freedom small distances Expanding Universe lect 2 45

46 around and below kt ª 200 MeV free quarks and gluons are gone and hadrons are formed Most hadrons are short lived and decay with τ ( ) s( ) = 10 8 s weak ints strong ints. << 1µs Example ( ) ( ) Λ 1115 = uds p + π p + μ + ν Leptons : muonand tauon decay weakly τ μ = 2 10 ( ) 6 s μ e + ν + ν μ e n π n+ e e 15 ( ) = τ τ s τ μ + ν + ν... μ μ Stableor long lived τ ( 17% ) Expanding Universe lect 2 46

47 pauze QUESTIONS?

48 Run out of unstable hadrons Neutrino decoupling/freeze out Big bang nucleosynthesis COOLDOWN TO A FEW MEV Expanding Universe lect 2 48

49 Cooldown to kt ª 10MeV After about 1ms all unstable particles have decayed Most, but not all, nucleons annihilate with anti nucleons (chapter 6) p+ p γ + γ 18 expect n baryons n γ ~ * 7 43 g = = 4 g* GeV 10 MeV we are left with g + e -, n e e, n m m,, n t and their anti particles TeV kt(gev) Expanding Universe lect 2 49

50 Around kt MeV: Big Bang Nucleosynthesis around few MeV: mainly relativistic g, e,n e, n m, n t + antiparticles in thermal equilibrium + few protons & neutrons weak interactions become very weak e ν ν + e ν + ν + e e i + n e + p + + p e + n n p+ e + ν e start primordial nucleosynthesis: formation of light nuclei (chapter 6) 2 n+ p H + γ MeV 2 H H 3 + n H γ + H He + γ Expanding Universe lect 2 50 i

51 Around kt 3MeV : Neutrino freeze out Equilibrium between photons and leptons + γ e + e ν ν i e μ τ ( ),, + = Weak interaction i i Weak interaction cross section decreases with energy s 2 σ ~ GF s = CM energy G π F = GeV Expanding Universe lect 2 51

52 Neutrino freeze-out at t 1s + e e ν ν i e, μ, τ + + = Weak interaction i i weak collision rate interactions/sec W = n σ v e+, relative lti e number density Cross section Rlti Relative (FD statistics) ~ T 3 ~ s ~ T 2 velocity H t 5 2 During expansion T decreases ( ) W when W << H or kt < 3MeV or t >1s T Neutrinos no longer interactt Neutrinos decouple and evolve independently neutrino freeze out Æ relic neutrinos Expanding Universe lect 2 52 T

53 Cosmic Neutrino Background Relic neutrinos are oldest relic of early universe decoupled at about 1s before CMB photons Should be most abundant particles in sky with CMB photons Should populate universe today as Cosmic Neutrino Background CνB or cosmogenic neutrinos what are expected number density and temperature today? Can we detect these neutirnos? oefening Expanding Universe lect 2 53

54 Cosmic Neutrino Background At few MeV there was thermal equilibrium between photons and leptons + ( γ ) e + e νi + νi i= e, μ, τ Number density neutrinos ª number density photons expected Temperature of neutrinos today T ( t ) 1.95K ν 0 = ν 0 E ( t ) mev expected density of relic neutrinos today: for given species (n e, n m, n t ) 3 3 N + N = N = 113 cm ν ν 11 CνB could explain part of Dark Matter : weakly interacting, massive, stable is Hot DM (chapter 7) γ Expanding Universe lect 2 54

55 Overview of radiation dominated era Quarks confined in hadrons g* 10 Neutrino Decoupling and nucleosynthesis Run out of relativistic particles ep recombination 3.4 Transition to GeV MeV matter dominated universe TeV kt(gev) Expanding Universe lect 2 55

56 Ω rad Part 4&6 Todays lectur re Ω baryons Part 7 Ω neutrino Part 5 ( ) Nanti ( B ) NB part 8 Ω CDM Part 5 CDM Rubakov Expanding Universe lect 2 56

57 Questions?

58 Part 6 matter and radiation decoupling Recombination of electrons and light nuclei to atoms Atoms and photons decouple at Z ~ 1100

Radiation-matter decoupling At t dec ª 380.

remain as today s CMB radiation Matter evolves independently atoms & molecules are formed stars,

59 Radiation-matter decoupling At t dec ª years, or z ª1100, or T ª 3500K matter decouples from radiation and photons can move freely & remain as today s CMB radiation Matter evolves independently atoms & molecules are formed stars, galaxies, Before t dec universe is ionised and opaque Population consists of p, H, e, g + light nuclei + neutrinos Expanding Universe lect 2 59

60 Protons and neutral hydrogen At kt ~ 3 MeV neutrino freeze out and start of BB nucleosynthesis most p and n bound in light nuclei (part 7) Photon density much higher than proton density observations N 10 γ N p ~10 Up to t ª y thermal equilibrium of p, H, e, g e + p H + γ Depends ondensities formation of neutral hydrogen of free e and p ionisation of hydrogen atom N e and N p N p = N e When kt < I=13.6 ev e + p H + γ T dec? Expanding Universe lect 2 60

61 Protons and neutral hydrogen Calculate Prob( electron bound in H atom) Prob ( electron unbound & relativistic ) f(t) number densityof free protons N p and of neutral hydrogen atoms N H as function of T N p N H + 1 2π mkt = = 2 NH NH Ne h 3 2 e I kt N e = density of free electrons m=electron mass At which T will universe run out of ionisedhydrogen? temperature at decoupling Expanding Universe lect 2 61

62 Decoupling temperature Rewrite in function of fraction x of ionised hydrogen atoms 2 N p N p x 1 2 π mk T x = = = 2 N p + NH NB 1 x NB h strong drop of x between kt ª ev or T between K fi ionisation stops around T~3500K e + p H + γ period of recombination of e and p to hydrogen atoms e + p H + γ Recombination stops when electron density is too small 3 2 e I kt Expanding Universe lect 2 62

63 Decoupling time Reshift at decoupling ( ) ( ) Full calculation ( ) + R t ktdec 3500K z dec = R t = = 2.75K z = 1100 dec ( ) kt 0 dec tdec = When electron density is too small there is no H formation anymore Photons freeze out as independent population = CMB 5 y start of matter dominateduniverse We are left with atoms, CMB photons and relic neutrinos + possibly exotic particles (neutralinos, ) Expanding Universe lect 2 63

64 Era of matter-radiation equality since 3 Ω T 4 Ω T baryonic matter photons Density of baryons = density of photons when Ω ( ) ( ) bar t bar t0 1 1 Ω t = Ω Ω t 1+ z = 1+ z = 870 ( 1+ z ) dec phot () phot ( ) 0 Density of matter (baryons + Dark Matter) = density of photons + neutrinos when Ω ( ) ( ) matter t Ωm t0 1 = = 1 Ω t Ω t 1+ z Ω ( ) ( ) phot+ neut Ω phot 0 1+ z 3130 Matter dominates over relativistic particles when Z < Expanding Universe lect 2 64

65 z~3000 z~1000 ρ + 31 ( ) ( + w 1 z ) J. Frieman Expanding Universe lect1 65

66 Summary Ene ergy pe er partic cle T(K) Time t(s) Expanding Universe lect 2 66

67 Expanding universe : content part 1 : ΛCDM model ingredients: Hubble flow, cosmological principle, geometry of universe part 2 : ΛCDM model ingredients: dynamics of expansion, energy density components in universe Part 3 : observation data redshifts, SN Ia, CMB, LSS, light element abundances ΛCDM parameter fits Part 4: radiation density, CMB Part 5: Particle physics in the early universe, neutrino density Part 6: matter radiation decoupling Part 7: Big Bang Nucleosynthesis Part 8: Matter and antimatter Expanding Universe lect 2 67

68 Questions?

69 Part 7 (chapter 6) Big Bang Nucleosynthesis formation of light nuclei when kt ~ MeV Observation of light element abundances Baryon/photon ratio Ω BAR

70 at period of neutrino decoupling when kt ~ 3 MeV Overview 1 e +, e γ, p, n, p,, n ( e, μ τ ), ν, ν, Anti particles are annihilated particles remain (part 8) N BAR Nγ p + p γ + γ 10 ~ 10 observed Fate of baryons? Big Bang Nucleosynthesis model Protons and neutrons in equilibrium due to weak interactions ν e + p e + n n p + e + ν e n and p freeze out at ~ 1 MeV Free neutrons decay Neutrons are saved by binding to protons deuterons n + p D + γ MeV Expanding Universe lect 2 70

71 Overview 2 When kt << I(D)=2.2 2 MVdi MeV dissociation i of D stops At kt ~ 60 KeV all neutrons are bound in nuclei Onset of primordial nucleosynthesis formation of nuclei li H, H, He, He, Be, Li model of BBN predicts abundances of light elements today At recombination ( y) nuclei + e atoms + CMB photons e + p H + γ CMB Atoms form stars, Large Scale Structures (LSS) Consistency of model: η light element abundances η CMB and LSS observations depend on N N photon 10 baryon 10 10? =? 10 10, ( light elem ) η ( CMB LSS ) Expanding Universe lect 2 71

72 neutron proton equilibrium When kt ~ 3 MeV neutrinos decouple from e, γ particle population consists of + e, e, νν, ( e, μτ, ) Most anti particles are annihilated p + p γ + γ Tiny fraction of nucleons is left Protons and neutrons in equilibrium due to weak interactions with neutrinos And neutron decay t = (885.7 ± 0.8)s γ, p, n, pn, ν e e + n e + + p ν + p e + n n p + e + ν Weak interactions stop when W << H n & p freeze-out 5 ( ) σ = kt ~08 ~0.8 MeV W t n v T H t T ( ) 2 e Expanding Universe lect 2 72

73 neutron/proton ratio vs Temperature As soon as kt << 1 GeV nucleons are non relativistic Probablity that proton is in energy state in [E,E+dE] P During equilibrium between weak interactions at nucleon freeze out time t FO kt ~ 0.8MeV Free neutrons can decay with t = (885.7 ± 0.8)s proton kt < M c E M p c 2 e kt = exp kt ( ) 2 Mc2 Mn M p c Δ N n = exp = e N p kt N n ( ) ( t ) FO N p ( t ) FO = ( ) Nn t exp t τ = Np () t exp( t τ ) p 2 kt Expanding Universe lect 2 73

74 Free neutrons and protons T(keV) weak interactions in equilibrium N t ( ) n () N t p 0.8MeV n,p freeze out 1s 60 KeV D freeze out Nuclear reactions dominate 1min Steigman 2007 t(s) t(s) 300 s Expanding Universe lect 2 74

75 Nucleosynthesis onset Non relativistic neutrons form nuclei through fusion: formation of deuterium 2 n + p H + γ MeV formation of 2 desintegration of H Photodisintegration of 2 H stops when kt 60 KeV << I(D)=2.2MeV free neutrons are gone And deuterons freeze out 2 H N n N p Free N n = Expanding Universe lect 2 75

76 Nuclear chains Chain of fusion reactions 2 n+ p H + γ MeV Production of light nuclei 2 3 H + n H + γ 2 H H H 3 He γ +4He2 + H +γ H + H He+ n He He 7 B L7 + +7i + e + γ Be n p ΛCDM model predicts values of relative ratios of light elements We expect the ratios to be constant over time Comparison to observed abundances today allows to test the standard cosmology model Expanding Universe lect 2 76

77 Observables: He mass fraction helium mass fraction Y ( ) 4y 2 ( N ) n Np ( 1+ ) n p M He = = = M He H y N N ( ) ( ) y = N N He H Is expected to be constant with time He in stars (formed long time after BBN) has only small contribution model prediction at onset of BBN : kt ~60keV, t~300s N n N p N = Y pred = 0.25 Observation today in gas clouds Y obs = ± Expanding Universe lect 2 77

78 Abundances of light elements Standard BB nucleosynthesis theory predicts abundances of light elements today example Deuterium Observations today D 5 ( DH ) 10 H = ± 4 BBN 10 Starts ktª80kev η 10 t(s) Abundances depend on baryon/photon ratio Expanding Universe lect 2 78

79 Parameter: baryon/photon ratio ratio of baryon and photon number densities Baryons = atoms N baryon Photons = CMB radiation η N photon In standard model : ratio is constant since BBN era (kt~80 kev, t~20mins) Should be identical at recombination time (t~ y) 000y) Observations : abundances of light elements, He mass fraction t~20mins CMB anisotropies from WMAP t~ y Expanding Universe lect 2 79

80 Abundances and baryon density W B h 2 B Observations Of light elements He mass fraction Measure η 10 CMB observations with WMAP measure W B h 2 abundances Model Predictions Depend on η 10 W B h 2 η Expanding Universe lect

81 CMB analysis Baryon photon ratio from CMB analysis PDG Ω B h = ± N B η 10 = = ± N γ ( ± ) pdg.lbl.gov g Expanding Universe lect 2 81

82 Light element abundances PDG 2013 Y p = ± ( ) 10 ( ) D/ H = 2.53 ± Li / H = 1.6± < η < ( ) %CL 10 pdg.lbl.gov g Expanding Universe lect 2 82

83 Questions?

84 Part 8 (chapter 6) matter-antimatter asymmetry y Where did the anti matter go?

85 What about antimatter? Antiparticles from early universe have disappeared! Early universe: expect equal amount of particles & antiparticles small CP violation in weak interactions p g + Expect e.g. N ( e ) N ( e ) = N ( p ) = N ( p ) primarycharged galactic cosmic rays: detect nuclei and no antinuclei Annihilation of matter with antimatter in galaxies would yield intense X ray and g ray emission not observed Few positrons and antiprotons fall in on Earth atmosphere : in agreement with pair creation in inter stellar matter Antiparticles produced in showers in Earth atmosphere = secundary cosmic rays Expanding Universe lect 2 85

86 Baryon number conservation Violation of baryon number conservation would explain baryon anti baryon asymmetry Baryon number conservation = strict law in laboratory 0 Ifno B conservation Æ proton decay is allowed + Some theories of Grand Unification allow for quark lepton transitions Search for proton decay in very large underground detectors, e.g. SuperKamiokande No events observed Lower limit on lifetime τ p > 10 ( ) 33 y p p e π K + ν Expanding Universe lect 2 86

87 Baryons and antibaryons Assume net baryon number = 0 in early universe Assume equilibrium between photons, baryons and anti baryons up to ~ 2 GV GeV p + p γ + γ Around10 20 MeV MVannihilation rate W << H A residu of baryons and antibaryons freeze out Expect N N B γ N B = 10 N γ 18 To do! Uitwerking meebrengen op examen Expanding Universe lect 2 87

88 Baryons and antibaryons Baryons, antibaryons and photons did not evolve since baryon/anti baryon freeze out Expect that today N N N B B γ = N B N B = 10 N γ 18 N 10-9Much η = B = 6.05 ± N too γ large! NB 4 < 10 N Observe 10 ( ) Explanation? B Expanding Universe lect 2 88

89 Baryon-antibaryon asymmetry Is the model dl wrong? Zacharov criterium : 3 fundamental conditions for asymmetry in baryon anti baryon density: starting from initial B=0 one would need Baryon number violating interactions Non equilibrium situation leading to baryon/anti baryon asymetry CP and C violation: anti matter has different interactions than matter Search at colliders for violation of C and CP conserving interactions Alpha Magnetic Spectrometer on ISS: search for antiparticles from space Expanding Universe lect 2 89

90 Expanding universe : content part 1 : ΛCDM model ingredients: Hubble flow, cosmological principle, geometry of universe part 2 : ΛCDM model ingredients: dynamics of expansion, energy density components in universe Part 3 : observation data redshifts, SN Ia, CMB, LSS, light element abundances ΛCDM parameter fits Part 4: radiation density, CMB Part 5: Particle physics in the early universe, neutrino density Part 6: matter radiation decoupling Part 7: Big Bang Nucleosynthesis Part 8: Matter and antimatter Expanding Universe lect 2 90

The expanding universe. Lecture 2

The expanding universe. Lecture 2 The expanding universe Lecture 2 Expanding universe : content part 1 : ΛCDM model ingredients: Hubble flow, cosmological principle, geometry of universe part 2 : ΛCDM model ingredients: dynamics of expansion,