At the second spontaneous symmetry breaking, out of the four massless bosons three acquire masses and become W + , W - and Z 0 Bosons.
Bosons which are massless have infinite range of influence such as photons. But bosons, the messenger particles, which have masses have their range of action drastically reduced. The examples are Intermediate Vector Bosons which have rest masses of the order of 90GeV with a range of action of the order of 10 -18 m and K + mesons, with rest mass 815MeV, have a range of action of 1 Fermi i.e.10 -15 m.
The title of this section is the fundamental constituent particles and their statistics. As we have already seen in SSPD_Chapter 1_Part 9_conclusion there are two statistics- Bose-Einstein Statistics and Fermi-Dirac Statistics.
The two statistics give two distinct distribution functions. The distribution function is the probability of finding the particles at different energy levels. The particles which obey Bose-Einstein Statistics are called Bosons(indistinguishable particles and have symmetric wave function) whereas the particles which obey Fermi-Dirac Statistics are called Fermions(distinguishable particles and have anti-symmetric wave functions).
Electrons, Protons and Neutrons are Fermions. Fermions always posses spin angular momentum equal to the integral multiple of (1/2)ћ. Fermions are real material particles and obey Pauli-Exclusion Principle. An elemental momentum phase space contains only two opposite spin Fermions. Because of Pauli-Exclusion Principle, if more than two fermions are squeezed in an elemental volume there will be strong repulsive force. Fermions behave claustrophobically that is two Fermions cannot occupy identical Quantum States in the same Cartesian Elemental Space. Electrons, protons and neutrons behave claustrophobically.
Contrary to these the carrier particles of the four forces are Bosons. Bosons are gregarious. They tend to gather in identical states if given the opportunity. An atom or a molecule with even number of e’s, p’s and n’s are bosonic in nature.
The carrier particles of gravitational force are gravitons .
The carrier particles of weak forces are intermediate vector bosons.
The carrier particles of electromagnetic force are photons.
The carrier particles of strong forces are Mesons ( k Mesons and π Mesons).
These particles obey Bose-Einstein Statistics and always posses spin angular momentum equal to 0ћ, 1ћ, 2ћ ……. A large number of Bosons can be accommodated in a very small volume and these particles will experience attraction. In this sense these are virtual particles.
Now we return to the expanding Universe.
As the energy level comes below 100GeV, the weak force freezes and intermediate vector bosons decouple from the hot soup and relic vector bosons are left over to this day.
Now the hot soup is an admixture of leptons , quarks and photons and only strong force and electromagnetic remain unified. Gravitational force was first to decouple leaving behind relic gravitons. Weak force was next to decouple leaving behind relic vector bosons.