About the format of the literature report

Transcription

1

2 About the format of the literature report Minimum 3 pages! Suggested structure: Introduction Main text Discussion Conclusion References

3 Use bracket-number (e.g. [3]) or author-year (e.g. Zackrisson et al. 2017) format for references in text

4 References Reference list at the end including at least: author(s), year, journal, journal number, page. Sometimes, article name and preprint number is also listed. Please try to avoid using web pages as references!

5 Outline Covers chapters 9 & 10 in Ryden

6 Grand Unification Gravity? Theory of Everything? Strong force Weak force EM t Planck : ~10-43 s t GUT : ~10-36 s t EW : ~10-12 s t

7 Grand Unification II

8 Phase Transitions The Universe underwent a phase transition when the temperature dropped below T GUT ~10 28 K Symmetry between strong and electroweak force lost Topological defects! Many GUT scenarios produce magnetic monopoles with mc 2 ~10 12 TeV

9 What is cosmic inflation? A short period of fast expansion, happening very early in the history of the Universe Inflation Scale factor Time

10 Why do we need inflation?

11 The flatness problem I Observationally: 1 Ω One can show that this implies, at the Planck time : 1 Ω Planck Hence, if the Universe is close to flat now, it was extremely close to flat in the past. Why is the Universe so close to flat? If this is a coincidence, it very, very improbable!

12 The horizon problem I Last scattering surface 0.98d hor 0.98d hor Observer How can the CMBR be almost completely isotropic, when opposite sides of the sky have never been in casual contact?

13 The horizon problem II θ hor = d hor ( t d A lss ) 0.4Mpc 13Mpc 2 degrees Regions in causal contact ~20000 patches in the CMBR sky Us

14 The magnetic monopole problem I Magnetic monopoles: zero-dimensional objects which act as isolated north or south poles of a magnet Many GUT models predict huge numbers of these! While subdominant at creation, they would soon come to dominate the energy density of the Universe Problem: No such objects have ever been observed! Where are the magnetic monopoles?

15 When did inflation occur? Scale factor Inflation One possible model: t start ~ s after the Big Bang t stop ~ s after the Big Bang a(t stop )/a(t start ) ~ e 100 ~10 43

16 The inflaton field I Consider a scalar field φ(r,t) with potential energy V(φ) V 0 False vacuum V(φ) True vacuum 0 0 φ φ 0

17 The inflaton field II V 0 V(φ) 0 0 φ φ 0

18 The inflaton field III V 0 V(φ) Oscillations Reheating 0 0 φ φ 0

19 Reheating If the Universe expands by a factor of ~e 100 Temperature drops by e -100 and the radiation energy denstiy gets extremely small How come it s not small after inflation then? Oscillations of φ around φ 0 Some of the energy of the inflaton field are being carried away by radiation These photons reheat the Universe Hence, no shortage of photons after inflation!

20 Slow-roll ε φ P φ 1 1 = 2 2 hc 1 1 = 2 2 hc ( φ + V φ 3 ( φ V φ 3 ) ) Slow roll : φ 2 << hc 3 V ( φ ) ε φ P φ V ( φ ) Negative pressure! Λ-like expansion! de Sitter phase!

21 Seeds for structure formation Inflation Prior to inflation: Microscopic quantum fluctuations Virtual particles created and annihilated After inflation: Quantum fluctuations blow up to macroscopic scales act as seeds for structure formation

22 Seeds for structure formation II Early Universe Primordial density fluctuations due to inflation Current Universe Primordial seeds have generated very complicated structure

23 Inflation as a solution to the flatness problem I The acceleration equation: a a 4πG = ( ε + 3P) 3c 2 During inflation, the Universe is temporarily dominated by a component with P < -ε/3 (i.e. w<-1/3), giving positive acceleration. One often assumes a cosmological constant Λ inflation to be responsible. Note: This constant is very different from the Λ driving the cosmic acceleration today. Λ inflation ~ Λ

24 Inflation as a solution to the flatness problem II Hubble parameter and scale factor during inflation: H a( t) inflation e = H Λ inflation t inflation 3 1/ 2 Number of e-foldings during inflation: N = H inflation ( t t stop start ) N ~ 100

25 Inflation as a solution to the flatness problem III 1 Ω( t stop ) = e 2N 1 Ω( t start ) Example: 1 Ω( t start ) 1 1 Ω( t stop ) 0 Inflation can effectively make a curved Universe flat!

26 Inflation as a solution to the horizon problem I The horizon problem

27 The solution

28 Inflation as a solution to the horizon problem II Horizon before and after inflation: d hor ( t 2 ) = c dt a( t) Before inflation : t t 1 2 d hor = 2ct start After inflation : ~ m d hor e N 3ct start ~ m

29 Inflation as a solution to the horizon problem IV Without inflation With inflation Us Us Regions in causal contact ~20000 patches in the CMBR sky Just one patch in the sky!

30 Inflation as a solution to the magnetic monopole problem I Expansion dilutes the number densities of objects, and inflation did this extremely efficiently

31 Inflation as a solution to the magnetic monopole problem II At the end of inflation : n monopoles ( t stop ) ~ e 300 n monopoles ( t GUT ) A realistic number density of monopoles at the GUT epoch would correspond to less than one monopole within the volume spanned by the last scattering surface

32 Eternal inflation I Once the inflaton field has come to rest at φ 0, inflation ends. But in some regions of space equantum fluctuations can make the inflation field move up the potential again Some regions keep inflating V 0 V(φ) 0 0 φ 0

33 Eternal inflation II

34 Eternal inflation III Differently inflated regions may end up with very different properties ( mutations ) Multiverse Good genes may promote further expansion (self-reproducing Universes).

35 Eternal inflation IV Future-eternal inflation Inflation will always continue (somewhere) Revives the perfect cosmological principle!

36 Stellar Black Holes Initial mass: Last stages: Remnant mass: 30<M/M solar SN BH ~ 3 20 M solar Supernova Stellar Black Hole Since the progenitors of stellar black holes are baryonic, these black holes cannot contribute much to the matter density of the Universe

37 Primordial Black Holes

38 Primordial Black Holes II Hawking radiation: Objects with M > kg would still be around! Observational constraints: BBNS abundances Gamma-ray background CMBR Unclear what happens at M Planck. Relics may form!

39 Intermission: What are you looking at?

40 What mass fraction of the particles in your body has at some point in the past been inside a star?

41 The Elements Atomic nuclei : Z = Number of protons N = Number of neutrons A = Nucleons = Mass number = Z + N H = Normal hydrogen nucleus (proton) H = Deuterium (hydrogen isoptope) He = Normal Helium

42 X, Y, Z

43 Abundances in Astronomy (number of A atoms / number B atoms) object [ A/ B] = log 10 (number of A atoms / number of B atoms) sun of

44 The Light Elements Note: BBNS required to explain abundances of 4 He and Deuterium!

45 The Heavy Elements Fusion: H He Heavier elements

46 Cosmic Ray Spallation

47 Important BBNS Reactions I: Proton-neutron freezeout Consider the Universe at t 0.1 s Pair production : γ + γ e n and n + ν n + e e + p + e + are held in equlibrium with each other p + e p + ν e Neutrinos freeze out of these reactions at t ~1 s Neutron-to-proton ratio frozen at n n /n p 0.2 Then follows neutron decay: n p + e +ν e :

48 Important BBNS Reactions II: Deuterium and Helium synthesis Consider the Universe at t s p + n d + γ The rightward direction starts to dominates once the photon temperature has dropped below the 2.22 MeV binding energy of Deuterium. Serious production of D does not start until t 300 s. Once we have Deuterium, several routes allow the formation of Helium:

49 The Detailed Solution Neutron decay

50 The Beryllium Bottleneck Even though you can form : 4 8 He+ 4 He 8 Be Be will decay back into He after just s Yet we know that the Universe has somehow managed to make heavier elements

51 The Beryllium Bottleneck II How do you make carbon? Solution: The Triple-Alpha process can take place in stars because of high temperatures (fast fusion of Helium)

52 The Beryllium Bottleneck III Triple-Alpha works because 4 He, 8 Be and 12 C happen to have finely tuned energy levels. Fred Hoyle (1950s) predicted a so far unknown excited level of 12 C, to explain why Carbon-based entities such as ourselves exist. Experimentalists later proved him right!

53 Primordial Abundances To test BBNS, one needs to measure the primordial abundances of the light elements, i.e. measure the abundances in environments unaffected by chemical evolution Helium: Low-metallicity HII regions Deuterium: Quasar absorption lines Lithium: Low-metallicitiy stars

54 Primordial Helium The blue compact galaxy IZw18

55 Primordial Deuterium

56 Primordial Lithium

57 BBNS A Big Bang Success Story This is how the success story is usually told but there may be more to this than meets the eye

58 Impressive agreement over 9 orders of magnitude Big picture probably correct But beware: The logaritmic scale hides discrepancies And what is the reason for the Li-7 mismatch?