Quarks, Leptons and the Big Bang

2006. 12.12

particle physics

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

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

Basic tools

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

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

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 n

eed not.

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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 lepto

ns(only weak force and possibly electromagnetic force)

e

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

Z

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

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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

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42222 cmcpE

E 22mc

Why are there more particles than antiparticles?

Some processes and the conservation laws of various kinds Pair annihilation/pair creation

Charge conservation

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Angular momentum and lepton number conservation

decay process is a weak interaction Muon decay (separate lepton number conservation is needed)

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Baryon conservation law

Forbidden process

Assign baryon number B=+1 to every baryon,B=-1 for antibaryon

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Hadrons

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

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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 particlehas S=-1 Strangeness is preserved in strong interactions

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p

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

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

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

Beta decay

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Weak force mediated by massive boson, short range force

W 80.6 GeV Z 91 GeV

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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)

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

General Gravity

Special relativity+gravitation matter and energy make spacetime curved

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)

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

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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.)

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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)

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

sec10 43

sec10 34 3010sec10 4

Black Holes

Gravitational field is so strong, once the light is trapped it cannot escape. Heuristically

R; black hole radiusFor the mass of sun, R few km (extremely dense object)

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Black hole theormodynamics

Black hole has temperature and entropy

1. Black hole temperature Black hole is not black (Hawking radiation; black body radiation with )

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1

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)

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