6 6 3 3 1 1 3 3 S s S A i A H s H P P / e / 6 6 3 3 2 2 1 h 1 2 2 . . 3 t 3 S s S G i G A l n A g g H s H n n P a : y P i i / e / a d d a a

s l l n y l l y y i n i a a n n u o g o u a a d e d B B r i r i i b o e b h t g h e l e l A l l ~ ~ . o . a a / a c / o k k B B d y d u u s v u s . . e e n r n c r c p m p a a o n o i i . . l a l l l L L i e s i c l c F b F u s u n n . o . r r e a e a b i a e e t t l C l s d s . . h d h t O t 2 n 2 r r r a a e a e K K v o v r r e e s s u m u z i z / / / r / : : p p t P t t t h h Nucleosynthesis and Baryogenesis

After these lectures, you should be able to: • Outline the key factors that determine the primordial Helium abundance • Comment on the expected abundances of the light elements • Discuss the observed abundances of the light elements • Describe their implications for the baryon density • List the Sakharov conditions for baryogenesis • Explain why they are required and how they might be achieved.

See also: • Liddle Chapters 12, A4 • http://www.astro.ucla.edu/~wright/BBNS.html • Kolb in Encyclopedia of Astronomy & Astrophysics, Murdin Nucleosynthesis: Overview

• The formation of nuclei – mostly Helium – from protons and neutrons – first few minutes after Big Bang

• Universe cools such that photons can no longer dissociate nuclei

• Key questions: – How much of each element formed? – What determines this? – How can we observe it? Nucleosynthesis

• The number of particles is given by the Maxwell- Boltzmann distribution: • If the temperature is high the reactions go both ways and there is equilibrium • As temperature lowers there is a tendency of one reaction to win. • So we can write the relative number densities with the ratio of these equations: Nucleosynthesis

n + νe ↔ p + e • k B T ~ 0.8 MeV

– Only n + ν e → p +e so no new neutrons are formed

– so N n /N p ~ exp(-1.3/0.8) ~ 1/5

Neutrons decay, half life 600s

• k B T ~ 0.1 MeV –t ~ 400 s : reverse reactions (4 He → n) stop

–N n /N p ~ 1/5 x exp( -ln2 x 400/600) ~ 1/8 • All remaining neutrons → 4 He p + n ↔ D 3 Y = 2 N / (N + N ) ~0.22 D + p ↔ He He n n p D + D ↔ 4He • This assumes all other reactions = 0. Y He = 2 N n / (N n + N p ) ~0.22

• The mass of Helium is 4 times the mass of the neutron roughly. • If all neutrons end up in helium 4 then the number of helium 4 particles is half the number of neutrons. • Therefore

• So: http://www.astro.ucla.edu/~wright/BBNS.html , based on data from Burles, Nollett & Turner (1999) http://www.physics.ohio- state.edu/~phillips/bang/bang.html • • E E R t RR R t d f f o o – – e f f e a a e n c t t c e e 4 4 R R ee a a s H H e e i l l c c o o t l l e e a a y f f c c c c t t d d h h t t cc i i e e e e o o o o o o p p m m n n n n e e v v f f i i n n r r s s ee a a t t d d r r r r t t b b ss s s e e y y i i o o : : o o a a ∝ ∝ n n n n r r d f f b b r r y y e o o a a n m m r r o o y y s i o o t n n n n y n n d d e e n n s s i i t t y y

http://www.astro.ucla.edu/~wright/BBNS.html Observations of the abundance of the light elements

• Quasar spectra

• Measure absorption lines Burles, Nollett, Turner astro -ph/9903300 Observations of the abundance of the light elements • Quasar spectra 0 0 3 3 0 9 9 / h p - o r t s s a r

• Measure absorption lines e n r u T , t t e l l o N , s e l r u B • Boxes indicate observations 2 –Converting gives: Ω b h ~ 0.02 –For h=0.72 gives Ω b = 0.04 Baryogenesis The creation of baryons. • Every particle has an anti- particle – positron is antiparticle of electron – antiproton is antiparticle of proton – baryon number of particle = -baryon number of antiparticle

• Early Universe: – 1 billion antiprotons – 1billion +1 protons – Particle + antiparticle ↔ radiation

• 1013K – Particle + antiparticle → radiation • Universe today = mainly matter Sakharov conditions

The conditions required for the creation of more matter than anti- matter (Sakharov 1967)

• Baryon number violation – Otherwise have same no. of particles and antiparticles

• C and CP violation – Parity of antiparticles is opposite to that of particles

• Departure from thermal equilibrium – Otherwise all reactions go both ways Likelihood of Sakharov conditions

• Baryon number violation – Never been observed – Predicted to occur in several theories.

• C and CP violation – CP violation discovered in 1964 (Cronin and Fitch) in interactions of K-mesons (kaons)

• Departure from non- thermal equilibrium – Expansion of the Universe Non-examinable Theories of baryogenesis

http://www.desy.de/desy-th/workshop2004/data/Shaposhnikov.pdf ShaposhnikovDESY 2004 END for now!!!