#bosons

The Weak Interaction

Amongst the four fundamental forces in nature, the weak interaction (aka the weak force or weak nuclear force) is the most commonly unheard of.

The weak force is mainly responsible for radioactive decay and fusion in stars. In our current understanding of the Standard Model, the weak interaction itself is caused by the emission or absorption of W and Z bosons. For example, this is most commonly seen in beta decay.

The exchange of W and Z bosons not only cause the transmutation of quarks (i.e. quark flavor changing) inside hadrons, but also (by definition) the hadrons themselves. For example, the process of beta decay allows for a neutron to transform into a proton. Given that a neutron is made up of two down quarks and one up quark, a down quark will need to emit a W¯ boson in order to transform into an up quark, thus allowing for the formation of a proton (which consists of two up quarks and one down quark). At the end of the process, the W¯ boson will then further decay into an electron and antineutrino.

It is called the weak force because its field strength is several orders of magnitude less than that of both electromagnetism and the strong interaction (however, gravity is the weakest of the four forces). The weak interactions are extremely short ranged (≈ 2 x 10^-3fm) because the intermediate vector bosons (W and Z) are very massive (with even higher masses than neutrons).

Unifying Fundamental Forces

Electromagnetism and the weak force are now considered to be two aspects of a unified electroweak interaction. This is the first step toward the unification the four fundamental forces.