Quarks, Leptons and the Big Bang

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 need not.

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)

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

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

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

 Why are there more particles than antiparticles?

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

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

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

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

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

Eightfold way ( hadrons with u,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

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

Beta decay

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

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

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 year old of the universe.)

 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 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  year Atoms form, light can travel farther

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)

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

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)