Quarks, Leptons and the Big Bang

1. Quarks, Leptons and the Big Bang 2006. 12.12

2. Study of fundamental interactions of fundamental particles in Nature Fundamental interactions 1. strong interactions 2. weak interactions 3. electromagnetic interactions 4. gravitational interactions particle physics

3. Gravitational force: very weak at atomic scale • Electromagnetic force: acts on all electrically charge particles • Strong force: the force binding nucleons together • Weak force: involved in beta decay acts on all particles

4. Basic tools • Special relativity and Quantum mechanics -> Relativistic Quantum Field Theory Schrodinger equation is valid only for nonrelativistic particle.

5. What is a particle? • Pointlike object with no internal structures. It is characterized by mass and spin. (cf. Baseball ) spin: intrinsic angular momentum spin without spin can be nonzero without rotation in space

6. Spin statistics theorem • Particle can have either half-integer spin or integer spin in units of • Particles with integer spin: Bosons Particles with half-integer spin: Fermions • Fermions should obey Pauli’s exclusion principle. No two identical particles can be at the same quantum state, while bosons need not.

7. Fundamental Particles • Fermions : building blocks of matter Paulis’s exclusion principle leptons: electron(e), muon( ), tau( ) neutrinos( ) quarks: u s t d b c Strong force acts on quarks and not on leptons(only weak force and possibly electromagnetic force)

9. Bosons : mediating the forces between fermions photons (light) no self interactions electromagnetic interactions gluons : quarks, nuclear force W, : weak interactions, decay gravitons : gravitational interactions

10. The emergence of the force • Coulomb force • When electrons emit and absorb (virtual) photons, momentum transfer occurs. Coulomb force is generated by this process. Virtual photons are those not satisfying energy-time uncertainty relation • All other forces arise in the same way

11. Relativistic Quantum Field Theory • Basic tools in theoretical particle physics • Combination of special relativity and the quantum mechanics -> • particle and antiparticle (same mass, opposite charge, opposite quantum numbers) > pair creation and annihilation occur • infinite degrees of freedom • strong, weak, electromagnetic interactions well described-> standard model

12. Why are there more particles than antiparticles?

13. Some processes and the conservation laws of various kinds • Pair annihilation/pair creation • Charge conservation

15. Angular momentum and lepton number conservation decay process is a weak interaction • Muon decay (separate lepton number conservation is needed)

16. Baryon conservation law • Forbidden process Assign baryon number B=+1 to every baryon, B=-1 for antibaryon

17. Hadrons • Bound states of quarks loosely called particles • Baryons (qqq): Fermions ex) proton, neutron Mesons ( ): Bosons ex) pions, Kaons

18. Another conservation law • Strangeness (strange quark) kaon and sigma always produced in pairs • process which does not occur • The above Kaon has S=+1 and sigma particle has S=-1 • Strangeness is preserved in strong interactions

19. Eightfold way ( hadrons withu,d,s quarks) • Classification of 8 spin ½ baryons and nine spin zero mesons via charge and strangeness

22. u,d,s … quark flavors • Why are quarks always bound? quark confinement • fractional charges for quarks proton (uud), neutron (udd) • Using the eightfoldway, Gellman predicted the existence of a new particle in a decuplet

23. Similar classification scheme can be applied for hadrons involving c,b,t quarks

24. Beta decay

25. Weak force mediated by massive boson, short range force W 80.6 GeV Z 91 GeV

26. Strong force (color force) • Messenger particles are gluons massless, quarks can have various color charges (red, yellow, blue) so can gluons in contrast with the photons • All hadron states are color neutral (quark confinement) Quantum chronodynamics (QCD) • Linear potential V~kr (color tubes)

27. Strong forces are responsible for quarks binding into baryons and mesons. They make the nuclear binding possible. • Quantum Gravity so far not by the relativistic quantum field theory based on the point particle but by the string theory

28. General Gravity • Special relativity+gravitation matter and energy make spacetime curved

29. Universe is expanding • Einstein’s greatest blunder(?) :introducing the cosmological constant for the Einstein’s field equation (No static universe solution for Einstein’s field equation) • Hubble’s observation (1929) All stars are moving away from us Universe is expanding (everywhere)

30. v=Hr H Hubble’s constant=71.0 km/s Mpc 1 Mpc=3 X km • If H is constant, then the estimated age of the universe is 1/H ( 13.7 X year) Based on the Big Bang scenario

31. Cosmic Background Radiation • The universe is filled with the 2.7 K radiation (microwave region) In the early universe, the temperature is very hot and the atoms cannot be formed. (kT=2m ) • After the atoms can be formed, lights can be travelled without scattering much about 379000 year old of the universe.)

32. If the cosmic background is too uniform this will be problematic for structure formation such as stars and galaxies. • Such slight deviation from uniformity has been observed indeed. 1992 Cosmic Backgrouns Explorer(COBE) 2003 Wilikinson Microwave Anisotropy Probe (WMAP)

35. Brief history of the Universe • concepts of the space and time can have meaning • inflation (factor of ) • Quarks can combine to form protons and neutrons. Slight excess of matter • 1min Low mass nuclei form Universe is opaque • 379000 year Atoms form, light can travel farther

36. Black Holes • Gravitational field is so strong, once the light is trapped it cannot escape. Heuristically R; black hole radius For the mass of sun, R few km (extremely dense object)

37. Black hole theormodynamics • Black hole has temperature and entropy 1. Black hole temperature Black hole is not black (Hawking radiation; black body radiation with )

38. 2. Black hole entropy is proportional to the surface area very large number for a black hole of solar mass • Entropy ~ number of states (?) • Classically black hole has few parameters (mass, charge and angular momentum)