Four consequences of the Lorentz transformation:
An alternative notation is often used for the transformation. This notation makes the equations a bit more compact and easier to manipulate. It comes about by realizing that we can organize the 4-vector as a 1-column by 4-row matrix. Number the rows of the matrix from 0 to 3, with (x0, x1, x2, x3) = (ct, x, y, z), then the Lorentz transformation is:
To be precise, the quantities in the above expression are tensors, not column vectors and matrices. However, we can interpret the expression as matrix multiplication with L given by the 4×4 matrix:
| L = | g | -gb | 0 | 0 |
| -gb | g | 0 | 0 | |
| 0 | 0 | 1 | 0 | |
| 0 | 0 | 0 | 1 |
| R = | cos q | -sin q | 0 |
| sin q | cos q | 0 | |
| 0 | 0 | 1 |
Finally, the dot product of two 4-vectors is written in this notation as:
| g = | 1 | 0 | 0 | 0 |
| 0 | -1 | 0 | 0 | |
| 0 | 0 | -1 | 0 | |
| 0 | 0 | 0 | -1 |
The Standard Model (SM) of particle physics emerged in the 1970's when quantum chromodynamics (QCD) and the electroweak theory (the two major components of the standard model Lagrangian) emerged from a throng of alternatives as best able to explain experimental observations. It has passed rigorous experimental confirmation since. We will discuss many of the important results in the coming weeks.
In the SM, all matter is constructed from a small number of fermions (spin ½ particles). These are the six quarks and six leptons, as shown in the table below.
| particle | charge | flavor | ||
|---|---|---|---|---|
| quarks | +2/3 | u | c | t |
| -1/3 | d | s | b | |
| leptons | -1 | e | m | t |
| 0 | ne | nm | nt | |
The existence of all of the fundamental particles has now been verified. The last two to be verified were the top quark, t (1995), and the tau neutrino, nt (2001). The four rows of the table group particles of the same electric charge with similar properties, while the three columns divide the particles into generations. While the matter around us is built using just the particles of the first generation (column), the existence of three generations has important consequences in the Standard Model. But why the number is three is not understood.
The leptons carry integral electric charge. The electron, e, is the familiar component of atoms. The muon, m, and tau, t are heavier versions of the electron. The neutral leptons are called neutrinos, the ethereal and nearly massless particles of the SM. Paired with each charged lepton is a different neutrino.
The quarks carry fractional charge +2/3 and -1/3 times the proton charge, denoted by |e|.