What is the reason for weak force?

[abi.ayan]

what property of elementary particles is reason for weak interaction? what I mean is as color charge is reason for strong force ,as electric charge is reason for EM force and as mass is reason for gravitational force what is reason for weak force?

 

[Chopin]

There are two properties, actually--one is called weak hypercharge, and the other is called weak isospin. They correspond to the U(1) and SU(2) symmetries of the Standard Model, respectively. The reason you don't hear about them as much is that they are related in a rather complicated way to the electric charge, and also to the chiral (non-parity-conserving) aspects of the Standard Model, so it's not as easy to say that a specific particle has a specific isospin/hypercharge number. But they are conserved quantities, and are related to the weak force in exactly the same way as color charge relates to the strong force, and mass relates to gravity.

 

[Lapidus]

The expand a bit on Chopin's excellent answer:

The fundamental gauge forces weak isospin and weak hypercharge are spontaneously broken by the Higgs field, the resulting forces of this symmetry breaking are the weak force and the E-M field.

Sometimes you read that the fundamental gauge group of the Standard Model is

SU(3)xSU(2)xU(1) which is spontaneously broken by the Higgs field to SU(3)xU(1)

The SU(2)xU(1) in the fundamental gauge group is the weak isospin and the weak hypercharge. The U(1) in the spontaneously broken gauge group is not the weak hypercharge, but the E-M field. So you see after symmetry breaking of the Higgs just two gauge groups are left: the color SU(3) gauge group and the E-M gauge group. The weak force that we observe is not a force with a gauge symmetry, it is not a massless force field, but a massive one.

The fundamental gauge groups weak isospin and weak hypercharge are hidden symmetries.

But all matter interact with the weak force, and all matter except the neutrinos interact with E-M force, which follows from the way the hidden and fundmental symmetries are structured.