# What is the Weak force?

In this Particle Physics books I'm reading it explains Weak force with Beta Decay, a Neutron turns into a Proton after emitting an electron, so after it emits an electron one of the neutrons down-quarks turn in to an up-quark, and for this there needs to be a force, which is the Weak force. This interaction is carried by the W and Z bosons. Now, I asked someone what Weak Force is and they said that it's the interaction between Protons and Electrons(Electronegativity). I would like to know what exactly the relation between the Weak Force and Electronegativity is, and if my initial definition of the Weak Force is wrong, I would appreciate it if I were corrected.

• Have you tried the Wikipedia page? What parts are unclear? – Emilio Pisanty Oct 20 '14 at 19:13
• Hi Riku, and welcome to Physics Stack Exchange! What have you done to try to find the answer yourself? Which other websites have you looked at? Textbooks? etc. – David Z Oct 20 '14 at 19:13
• @DavidZ and Emilio, The OP says the books he read, explain the weak force but asks for further clarification – Nikos M. Oct 20 '14 at 19:16
• @davidz The main textbook I'm using is "Teilchenphysik" by Michael Schönitzer, I looked at the wikipedia page too, the thing that confuses me is this part about the interaction between electrons and protons, I understand the part about Weak force making beta decay possible but I don't understand how this is related to electronegativity. – Riku Oct 20 '14 at 19:18
• "they said that it's the interaction between Protons and Electrons(Electronegativity)" This is wrong. While there is a weak interaction between protons and neutrons it is swamped by the plain electromagnetic interaction and it has nothing to do with chemistry. "Electronegativity" is a chemistry idea and applies at much longer length scales and much lower energy scales than any manifestation of the weak force. – dmckee Oct 20 '14 at 19:53

The "forces" used in current Standard Model of physics (the quotes are on purpose since there are other forces as well, in different context), are:

1. "Strong Nuclear Force", in essence keeps the nuclei together, nuclear fission is based on this

2. "Weak Nuclear force", in essence is a type of nuclear force (associated with nuclei) but has a smaller coupling constant, applies to intermediate distances than strong nuclear force and is involved in nuclei transformations like beta decay (coupling constant gives the relative measure of the force application to specific energy ranges, that is why the "weak" nuclear force, in contrast to "strong" nuclear force, one can see this as two facets of the same force acting in different energy ranges if one wishes to do so)

3. "Electromagnetic force", in essense a force with applications in the distances and particles between weak nuclear force and gravity (see next). Most of everyday interactions are of electromagnetic nature. has a smaller coupling constant than nuclear forces.

4. "Gravity force", well ypu know about this (hopefuly and the rest of us as well :))

In relation to weak force and electronegativity, this is not, in general, a ubiquitus conection or relation.

Weak force is invoved in many types of nuclear particle reactions (only some of which involve electrons), others involve muons or pions or other particles, so the connection with electrons and electronegativity is only partially standard.

However, what is standard (and is a basic result of physics referred to as Noether's theorem) is that in all these interactions, there are (generalised) charges (of which electric charge may be one) that are conserved. For example color is a type generalised charge that can be conserved in an interaction. So this the connection with charges (of which electric is one) that was the content of the question (and comment)

• The 4 forces are clear to me for the most part, what isn't so clear is the relation between weak force and electronegativity (if there is any). Also I'm not entirely sure if the definition of weak force I posted above is correct. – Riku Oct 20 '14 at 19:24
• @Riku, hmm i'll try to edit the answer to reflect your comment, give me a couple of minutes – Nikos M. Oct 20 '14 at 19:26
• @Riku, what exactly do you mean by Electronegativity? i dont think you mean the link? This would be wrong (in general) even if it might hold in some cases of nuclear particle reactions – Nikos M. Oct 20 '14 at 19:28
• as I said in the OP, I asked someone about Weak Force and they told me that it's the interaction between protons and electrons i.e. electronegativity, that is what left me confused, I asked if there was any relation between the weak force and electronegativity, but that seems to not be the case? – Riku Oct 20 '14 at 19:31
• And I was also asking for further clarification on the weak force – Riku Oct 20 '14 at 19:33

The weak force acts on particle that have weak hypercharge, just as electromagnetism acts on objects with electrical charge and gravity acts on objects with mass.

All the quarks and leptons have weak hypercharge, so the weak force act on them.

The description you have been given of beta decay is incomplete because it does not conserve the overall lepton number (one of the few symmetries that the weak force respects). That is, you've been told $$n \to p^+ + e^- \,,$$ but the correct reaction includes an anti-neutrino $$n \to p^+ + e^- + \bar{\nu}_e \,.$$

The weak force also manifests in flavor changing hadron decays such as $$K^+ \to \pi^0 + \mu^+ + \nu_\mu \,.$$ and in parity violating scattering.

• Ah, right! The textbook also mentions the part about the neutrino (it didn't say anti-neutrino though) but it said that they won't go into it much because it'll be discussed in a later chapter. I guess that's why I forgot it. Thanks for the clarification! – Riku Oct 20 '14 at 19:57